From Wikipedia, the free encyclopedia
.^ A magnetic field represents stored energy and .- Magnetism: quantities, units and relationships 18 September 2009 7:28 UTC info.ee.surrey.ac.uk [Source type: Academic]
^ Treatment with the iron chelator deferiprone also blocked the effects of magnetic fields on brain cell DNA, suggesting the involvement of iron.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ Hz magnetic field at 7 mT in the presence of iron cations.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ The magnetic relative permeability (mu) for Iron at extremely high temperatures and pressures is not accurately known, but it seems to rise with temperature and seems certain to be at least 10,000.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
^ The magnetic field pattern around a bar magnet is created by the superposition of the dipole fields of the individual iron atoms.
^ The increasing magnetic field causes electrons to circulate (current) around the second coil in such a way as to oppose the increasing magnetic field that the first coil is trying to establish.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ (In this way, they resemble the field lines of an iron bar magnet, which arch from the north to the south poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ E × B d v This predicts something specific about the direction of propagation of a light wave: it must be along the line perpendicular to the electric and magnetic fields.
^ Moreover, the shifting magnetic field outside the star must drive electrical currents along arched magnetic field lines.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
However, these lines do not
precisely represent the field lines of the magnet, as the presence of the iron filings somewhat alters its magnetic field.
.^ This electric field is not created by charges .
^ In particular, the fact that electric currents create magnetic fields.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
.^ Infer the direction of the magnetic field.
^ The magnetic field varies in both magnitude and direction (i.e., it is a vector field) in a volume of space around a magnet or around a loop of current.- "MAGNETIC UFO" 13 January 2010 10:13 UTC brumac.8k.com [Source type: Academic]
^ The electric field at point P is , and the magnetic field is .
[1]
.^ FIELD OF THE INVENTION [0001] The present invention relates to a magnetic field control method and a magnetic field generator, and more specifically, to a magnetic field control method and a magnetic field generator in which an orientation of a magnetic field at a target position is changed to an arbitrary direction.- Magnetic Field Control Method and Magnetic Field Generator - Patent application 13 January 2010 10:13 UTC www.faqs.org [Source type: Reference]
^ Diamagnetic materials have the interesting property that they are repelled from regions of strong magnetic field, and it is therefore possible to levitate a diamagnetic object above a magnet, as in figure h .
^ Diamagnetism is generally a much weaker effect than paramagnetism, and is easily masked if there is any trace of contamination from a paramagnetic material.
.^ Magnetic fields curl around currents.
^ The torque on a current loop in a magnetic field.
^ The magnetic field generator according to claim 3 or 4, wherein at least one of the magnetic field generating units is constituted by a plurality of permanent magnets and a holding member holding the permanent magnets.- Magnetic Field Control Method and Magnetic Field Generator - Patent application 13 January 2010 10:13 UTC www.faqs.org [Source type: Reference]
.^ The relationship between the change in the magnetic field, and the electric field it produces.
^ Do we have infinite energy in the resulting magnetic field?
^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
(See
electromagnetism.)
.^ Melatonin aspects of exposure to low frequency electric and magnetic fields.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ Geometry of the electric and magnetic fields .
^ Prove that in an electromagnetic wave, half the energy is in the electric field and half in the magnetic field.
.^ Where is the moving charge responsible for this magnetic field?
^ In her frame of reference, it's the bar magnet that is moving.
^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
.^ H-field alias magnetizing force .- Magnetism: quantities, units and relationships 18 September 2009 7:28 UTC info.ee.surrey.ac.uk [Source type: Academic]
^ Geometry of the electric and magnetic fields .
^ Prove that in an electromagnetic wave, half the energy is in the electric field and half in the magnetic field.
.^ This article proposes a comprehensive theory that logically explains ALL the peculiar findings, as well as a mathematically and physically logical description of the source itself.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
B and H
|
|
Alternative names for H
| name |
used by |
| magnetic field intensity |
electrical engineers |
| magnetic field strength |
electrical engineers |
| auxiliary magnetic field |
physicists |
| magnetizing field |
physicists |
|
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ We can also anticipate that the magnetic field will be a vector.
^ Magnetic Grid Layer After extensive research into magnetic fields and the use of magnets in alternative health care, engineers designed a magnetic grid pattern with two distinct benefits: First, the field distribution is even, so that all parts of the body benefit equally.- MAGNETIC FIELD THERAPY - MAGNETIC MATTRESS PADS 13 January 2010 10:13 UTC www.shoppingsolution.com [Source type: General]
[2] There are many alternative names for both, though. (See sidebar.)
.^ B = 0 Maxwell's Equation for B You could argue that B indicates better the strength of a magnetic field than does the 'magnetic field strength' H! This is one reason why modern authors tend not to use these names and stick instead with 'B field' and 'H field'.- Magnetism: quantities, units and relationships 18 September 2009 7:28 UTC info.ee.surrey.ac.uk [Source type: Academic]
^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
^ These data further support a role of free radicals on the effects of magnetic fields.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ MR ( magnetoresistive ) A technology based on the effect where electrical resistance in a material changes when brought in contact with a magnetic field .- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
^ Based on counts of supernovae within many other galaxies like the Milky Way, this rate is estimated in the range of 1 per 100 years.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ This hypothesis could have an important implication for the possible health effects associated with exposure to extremely low-frequency magnetic fields in the public and occupational environments.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ This electric field is not created by charges .
^ Where is the moving charge responsible for this magnetic field?
^ Definition in terms of the force on a moving particle .
In
SI units, the Lorentz force equation is
where
× is the
vector cross product.
.^ The unit of magnetic field, the tesla, is named after Serbian-American inventor Nikola Tesla.
^ Although the relationship E ≤ftrightarrow q between electric fields and their sources is unalterably locked in by Gauss's law, that's not what we see in practical measurements.
^ Early in the nineteenth century, Carl Friedrich Gauss (1833; 1839) used many measurements from all over the world to characterize the earths field.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
An alternate working definition of the B-field can be given in terms of the
torque on a magnetic dipole placed in a B-field:
for a
.^ Example 1: The magnetic dipole moment of an atom .
^ The distant field of a square dipole turns out to be simple, and is no different from the distant field of any other dipole with the same dipole moment.
^ Apparently, nearly all the atoms in such a magnet are oriented randomly, and do not contribute to the magnet's dipole moment.
.^ Now, in the last 20 years or so, the magnetic field has become erratic.- A Weakening Magnetic Field and Emerging Sunspot Cycle 24... What Does This Mean for Planet Earth and All Species? | KnowTheLies.com - The Truth is Hidden in Plain View... 13 January 2010 10:13 UTC www.knowthelies.com [Source type: FILTERED WITH BAYES]
^ For these reasons, let's look at an alternative method of defining the magnetic field which, although not as fundamental or mathematically simple, may be more appealing.
^ The effect occurs only when the magnetic field is changing, and it appears to be proportional to the derivative ∂ B /∂ t , which is in one direction when the field is being established, and in the opposite direction when it collapses.
H is defined as a modification of
B due to magnetic fields produced by material media, such that (in
SI):
where
.^ H = B / μ 0 - M Sommerfeld Field Equation This formula applies generally, even if the materials within the field have non-uniform permeability or a permanent magnetic moment .- Magnetism: quantities, units and relationships 18 September 2009 7:28 UTC info.ee.surrey.ac.uk [Source type: Academic]
^ The result is that when a magnetic field enters a high-permeability material, it tends to twist abruptly to one side, and the pattern of the field tends to be channeled through the material like water through a funnel.
^ A magnetically permeable material is placed at the center of a solenoid.
[3] .^ H = F m / l e ampere-turns per metre The field produces magnetic flux density - .- Magnetism: quantities, units and relationships 18 September 2009 7:28 UTC info.ee.surrey.ac.uk [Source type: Academic]
^ The oval lines are contours of constant current density (amperes per square meter).- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
^ Exposed to an electric field E , a conductor responds with a current per unit cross-sectional area J =σ E .
[4].^ In fact, if you can treat the permeability as being linear, then the constants N , l e , μ and A e can be lumped together into one constant for the winding which is called (surprise!- Magnetism: quantities, units and relationships 18 September 2009 7:28 UTC info.ee.surrey.ac.uk [Source type: Academic]
^ L = N × d Φ / d I Equation TMO If the core material's permeability is considered constant then the relation between flux and current is linear and so: .- Magnetism: quantities, units and relationships 18 September 2009 7:28 UTC info.ee.surrey.ac.uk [Source type: Academic]
.^ A charged particle is in a region of space in which there is a uniform magnetic field .
^ On page 667, I proved that H ||,1 = H ||,2 at the boundary between two substances if there is no free current and the fields are static.
^ All the compasses pointed north indicating that there was no large magnetic anomaly in the area.- "MAGNETIC UFO" 13 January 2010 10:13 UTC brumac.8k.com [Source type: Academic]
.^ Though studies are being done to see if there is a link between it and tumors of the brain and central nervous system, there is no definitive link between the two, the institute says on its Web site.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ On page 667, I proved that H ||,1 = H ||,2 at the boundary between two substances if there is no free current and the fields are static.
^ There is no difference between the “stuff” in one end of the magnet and the other, q .
.^ Since the hysteresis curve is nonlinear, and is not a function (it has more than one value of M for a particular value of B ), a ferromagnetic material does not have a single, well-defined value of the permeability μ; a value like 4,000 for transformer iron represents some kind of a rough average.
^ Ferromagnetism is a phenomenon in which a material tends to organize itself so that it has a nonvanishing magnetic field.
[5]
See
History below for further discussion.
The magnetic field and permanent magnets
.^ A changing electric field can produce a magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
^ If the current is a DC (direct current), the magnetic field is steady, like that form a permanent magnet.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Suppose, for example, that the axis of the coil is aligned with the magnetic north-south.
^ Today, the magnetic field focuses space radiation towards the far north and south where few people live.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ The rotating Iron Core would necessarily have its rotational axis on the line connecting the North and South Magnetic Poles.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
.^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ I suggested that if such motions were fast enough, they could cause magnetic polarity reversals.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
^ Diamagnetic materials have the interesting property that they are repelled from regions of strong magnetic field, and it is therefore possible to levitate a diamagnetic object above a magnet, as in figure h .
.^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Today, the magnetic field focuses space radiation towards the far north and south where few people live.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ The bizarre implication was that at some point the entire global magnetic field had done a sudden 180-degree flip, completely reversing direction.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ Let's assume a magnetic field of this form, and see what Maxwell's equations tell us about it.
^ For more information, see my review article, Physics in Ultra-strong Magnetic Fields .- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Learn More About Current Research From Europe From Our New Report on Pulsed Magnetic Therapy Download for Free by Clicking Here .
Force on a magnet due to a non-uniform B
.^ Worse yet, the various movements of the location of the two Magnetic Poles often seem to have no relationship with each other.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ But as they were well aware, magnetic north keeps moving, wandering about near the pole as the field gradually changes.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ However, Barnes also argues strenuously against the standard theory of dynamo action generating the Earth's magnetic field.- Creation Science and the Earth's MagneticField 13 January 2010 10:13 UTC www.talkorigins.org [Source type: FILTERED WITH BAYES]
^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
^ All matter on Earth assists in creating this field and so becomes charged with this magnetic resonance, displaying different results, dependant on the substance.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Infer the direction of the magnetic field.
^ In example 9 , the outer loop has a current in the opposite direction, so it contributes a field that is into the page.
^ And this magnet, because a magnetic field is a force field, will align itself with the Earth's magnetic field.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ Make a sketch showing the direction of motion and the direction of the field, and show that the resulting force is in the right direction to produce circular motion.
^ Furthermore, reversing the current I in our example would have reversed the force, which would only make sense if the magnetic field had a direction in space that could be reversed.
^ When an object experiences a force with constant magnitude, which is always perpendicular to the direction of its motion, the result is that it travels in a circle.
.^ The torque on a current loop in a magnetic field.
^ Has the earths magnetic field ever flipped?- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
^ So, what does this sighting have to do with a magnetic field?- "MAGNETIC UFO" 13 January 2010 10:13 UTC brumac.8k.com [Source type: Academic]
.^ Becuase the magnet has two poles, then the particle would be a magnetic dipole.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
^ Worse yet, the various movements of the location of the two Magnetic Poles often seem to have no relationship with each other.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
^ Having two poles, one north and one south, it has the same shape as the field from a tiny but powerful bar magnet right at the center of the sphere.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
.^ But the nature of the field is evident in all magnetic fields.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
^ Dipole field around a magnetized sphere.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
[6][7]
Mathematically, the force on a magnet having a magnetic moment
m is:
[8]
where the
.^ As the gradiometer rod was turned away from the direction of maximum frequency (maximum gradient), i.e., rotated to the left, right, upward or downward, the frequency decreased considerably.- "MAGNETIC UFO" 13 January 2010 10:13 UTC brumac.8k.com [Source type: Academic]
^ But when we multiply electric field by distance, what we get is an indication of the amount of work per unit charge done on a test charge that has been moved through that distance.
^ The upward direction of the maximum gradient suggests that the source may have been at or above the tops the pine trees.- "MAGNETIC UFO" 13 January 2010 10:13 UTC brumac.8k.com [Source type: Academic]
.^ The energy density of a light wave is related to the magnitudes of the fields in a specific way --- it depends on the squares of their magnitudes, E 2 and B 2 , which are the same as the dot products E ⋅ E and B ⋅ B .
^ A dot product is zero when the vectors are perpendicular, so only the top and bottom edges contribute to Γ.
^ A circulation is defined by breaking up a loop into tiny segments, d s , and adding up the dot products of these distance vectors with the field.
)
.^ An infinite magnetic circulation Γ B can only be produced by an infinite magnetic field, so without the ∂Φ E /∂ t term, Maxwell's equations predict nonsense: the edge of the surface would experience an infinite magnetic field at one instant, and zero magnetic field at all other times.
^ An easy way to approach this is to use the fact that vB has the same units as E , which can be seen by comparing the equations for magnetic and electric forces used above.
^ It only tells us that we can't make them using magnetic monopoles.
.^ Plugging all these values into the equation gives a result of a Magnetic Flux of around 4 * 10 25 Maxwells.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
^ This is because the current in the coil sets up its own magnetic field, and that field exerts a torque on the magnet.
^ The charge by itself up above the wire is like a test charge, being used to determine the magnetic and electric fields created by the wire.
.^ Find the induced magnetic field at a point between the plates, at a distance R from the axis.
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ There are two primary methods by which one can generate a mathematical description of the Earth's magnetic field, or any other field for that matter.- Creation Science and the Earth's MagneticField 13 January 2010 10:13 UTC www.talkorigins.org [Source type: FILTERED WITH BAYES]
.^ One solution to this problem relies on the fact that the force experienced by a charged particle in an electric field, F E =q E , is independent of its velocity, but the force due to a magnetic field, F B =q v × B , isn't.
^ The magnetic force on the lone charge q due to the current I is .
^ This would therefore mean that the only remaining rotation that could induce a magnetic field today would be due to the daily rotation of the Earth.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
.^ These lodestones have been charged by the Earth, and thus are harmoniously in tune with the human bodies' frequencies as well, they have for thousands of years been successfully used in the healing arts.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The simple dipole model can be used to calculate the equivalent source strength, Bo, from the gradient measured by J's instrument if the distance to the source is known or assumed.- "MAGNETIC UFO" 13 January 2010 10:13 UTC brumac.8k.com [Source type: Academic]
^ When charged particles are moving, they make magnetic fields as well.
.^ Magnetic fields have no sources or sinks.
^ The fact that this theory suggests that the Earth's Magnetic Field measured at the surface (or in space) is a result of the vector sum of two much stronger but generally opposing source fields, enables straightforward explanation of many of the peculiar characteristics measured in the Earth's Magnetic Field.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
^ For instance, what should happen to the radius when the magnetic field is made stronger?
.^ Today, the magnetic field focuses space radiation towards the far north and south where few people live.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ By symmetry, the field in this plane cannot have any component in the radial direction (inward toward the dipole, or outward away from it); it is perpendicular to the plane, and in the opposite direction compared to the dipole vector.
^ This same problem applies equally to explaining the short-term variations in both magnetic field strength and direction and in explaining erratic magnetic pole migration.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ If the velocity vector is initially perpendicular to the field, then the curve of its motion will remain in the plane perpendicular to the field, so the magnitude of the magnetic force on it will stay the same.
.^ Where is the moving charge responsible for this magnetic field?
^ Infer the direction of the magnetic field.
^ The torque on a current loop in a magnetic field.
.^ The present premise does NOT require this, and includes a mechanism for explaining the separation of the Geographic and Magnetic Poles.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
^ We, and all other living things, are surrounded by a magnetic field extending out into space from our bodies, and the fields from the brain reflect what is happening in the brain.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Humans have an innate ability to sense the direction of magnetic north, and this ability can be blocked by placing a bar magnet against a person's forehead for only fifteen minutes!- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ DANIEL LATHROP: We apply a large magnetic field on the sodium flow inside the sphere, and you can get a feel for how strong the magnetic field is.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ My 1990 paper shows that as upwelling core fluid expels magnetic flux, it also generates loops of new lines of force in the reversed direction.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
.^ The torque on a current loop in a magnetic field.
^ A much more useful building block is a square current loop.
^ Likewise, as shown in figure f , if we could find the magnetic field of a square dipole, then we could find the field of any planar loop of current by adding the contributions to the field from all the squares.
[9]
Torque on a magnet due to a B-field
.^ Infer the direction of the magnetic field.
^ The torque on a current loop in a magnetic field.
^ A compass needle in a magnetic field experiences a torque which tends to align it with the field.
.^ The torque on a current loop in a magnetic field.
^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
The torque
τ on a small magnet is proportional both to the applied B-field and to the magnetic moment
m of the magnet:
where × represents the vector cross product.
.^ The torque on a current loop in a magnetic field.
^ A compass needle in a magnetic field experiences a torque which tends to align it with the field.
^ A dipole tends to align itself to the surrounding magnetic field.
.^ However, a compass needle doesn't point at true north, at the real geographical North Pole, instead it points at magnetic north.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ It's what makes our compasses point north.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ Today the Earth's magnetic field runs from south to north—which is why compass needles point towards the North Pole—and recent lava flows record a field pointing north.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ It's what makes our compasses point north.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ Infer the direction of the magnetic field.
^ A compass needle in a magnetic field experiences a torque which tends to align it with the field.
.^ An electric motorized clock, plugged into a wall socket, produces an amazingly high magnetic field because of the small electric motor that runs it.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
^ The charge by itself up above the wire is like a test charge, being used to determine the magnetic and electric fields created by the wire.
.^ A magnetic field in the form of a sine wave.
^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
^ These data further support a role of free radicals on the effects of magnetic fields.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ In particular, the fact that electric currents create magnetic fields.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Scientists believe that just as the electric currents produce the magnetic field, so the magnetic field produces the electric currents.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ These processes use artificial electrical energy, which has within its structure a frequency composition different to that of nature.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Summing up, we propose that magnetic fields initiate an iron-dependent free radical generation process in cells, which can lead to genotoxic changes and/or cell death.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ Simply stated, it has been shown that turbulent motions within an electrically conductive fluid will generate magnetic fields.- Creation Science and the Earth's MagneticField 13 January 2010 10:13 UTC www.talkorigins.org [Source type: FILTERED WITH BAYES]
.^ We're already seeing acute effects that are noticed within minutes of using a cell phone.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ MR ( magnetoresistive ) A technology based on the effect where electrical resistance in a material changes when brought in contact with a magnetic field .- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
Visualizing the magnetic field using field lines
.^ Treatment with the iron chelator deferiprone also blocked the effects of magnetic fields on brain cell DNA, suggesting the involvement of iron.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ Hz magnetic field at 7 mT in the presence of iron cations.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ The magnetic field pattern around a bar magnet is created by the superposition of the dipole fields of the individual iron atoms.
The field lines are not precisely the same as the isolated magnet; the
magnetization of the filings alters the field somewhat.
.^ The arrows map the magnetic field B .
^ Infer the direction of the magnetic field.
^ Milligauss is a unit of flux density , not magnetic field strength, but the difference is not important.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Infer the direction of the magnetic field.
^ In addition to this, the STRENGTH of the measured magnetic field also has a number of variations and drifts.- http://mb-soft.com/public/tecto2.html 13 January 2010 10:13 UTC mb-soft.com [Source type: FILTERED WITH BAYES]
^ MARIO ACUNA: So here is my spring, here's my magnet, and if I pass an electrical current through my spring and measure the disturbance of my magnet, which is inside, then I can transmit back to Earth the information about the strength and the direction of the field we are trying to measure.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ Infer the direction of the magnetic field.
^ The arrows map the magnetic field B .
^ Its strength is proportional to the rate at which the field changes.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
An alternative method of visualizing the magnetic field which greatly simplifies the diagram while containing the same information is to 'connect' the arrows to form "magnetic
field lines".
.^ Infer the direction of the magnetic field.
^ The current is at right angles to the direction of the changing magnetic field, and is strongest near the extremities of a person.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The bizarre implication was that at some point the entire global magnetic field had done a sudden 180-degree flip, completely reversing direction.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
As seen here, the magnetic field points towards a magnet's south pole and away from its north pole.
.^ MR ( magnetoresistive ) A technology based on the effect where electrical resistance in a material changes when brought in contact with a magnetic field .- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
^ Treatment with the iron chelator deferiprone also blocked the effects of magnetic fields on brain cell DNA, suggesting the involvement of iron.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ Because the other studies reporting effects of magnetic fields on DNA were carried out under continuous exposure conditions, the results of Ivancsits et al.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ Figure 1a shows the magnetic lines of force outside a magnetized sphere.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
^ Figure b shows a mysterious curly magnetic field.
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
.^ The earth's magnetic field impacts climate .- A Weakening Magnetic Field and Emerging Sunspot Cycle 24... What Does This Mean for Planet Earth and All Species? | KnowTheLies.com - The Truth is Hidden in Plain View... 13 January 2010 10:13 UTC www.knowthelies.com [Source type: FILTERED WITH BAYES]
^ Infer the direction of the magnetic field.
^ Recent trends in the earths magnetic field.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
.^ We can also anticipate that the magnetic field will be a vector.
^ In reception, both conductors are bathed in the same electric and magnetic fields, so an emf that adds current on one side subtracts current from the other side, resulting in cancellation.
^ If this single particle qualifies as a current, then it should be surrounded by a curly magnetic field, just like any other current.
.^ Infer the direction of the magnetic field.
^ The electric field at point P is , and the magnetic field is .
^ As it spins, the nearby magnetic field changes.
[10] .^ As it spins, the nearby magnetic field changes.
^ These data indicate an interaction between intensity and duration of exposure on biologic effects of magnetic fields.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ If the sample is initially unmagnetized, 1, and a field H is externally applied, the magnetization increases, 2, but eventually becomes saturated, 3, so that higher fields do not result in any further magnetization, 4.
.^ Figure 1a shows the magnetic lines of force outside a magnetized sphere.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
^ For a purely dipolar field, the equation r = R sin 2 q relates the radius r and colatitude q of each point on a given line of force, R being the value of r where the line of force intersects the equatorial plane.- The Earth’s Magnetic Field is Still Losing Energy 13 January 2010 10:13 UTC www.creationresearch.org [Source type: Academic]
^ It is that a magnetic field is a primary force in the same way as gravity is seen as a primry force.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
.^ Treatment with the iron chelator deferiprone also blocked the effects of magnetic fields on brain cell DNA, suggesting the involvement of iron.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ Hz magnetic field at 7 mT in the presence of iron cations.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ If the current is a DC (direct current), the magnetic field is steady, like that form a permanent magnet.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
^ They actually trap in...they record the Earth's magnetic field.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ An electric motorized clock, plugged into a wall socket, produces an amazingly high magnetic field because of the small electric motor that runs it.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Infer the direction of the magnetic field.
^ Describe the direction of the magnetic field that would be produced, at its center, by the loop in the x - y plane alone.
^ Acting like microscopic compass needles, they record not only how strong the field is, but also in what direction it is pointing.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ It's what makes our compasses point north.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
^ For reasons not fully understood, CMEs in even-numbered solar cycles (like 24) tend to hit Earth with a leading edge that is magnetized north.- A Weakening Magnetic Field and Emerging Sunspot Cycle 24... What Does This Mean for Planet Earth and All Species? | KnowTheLies.com - The Truth is Hidden in Plain View... 13 January 2010 10:13 UTC www.knowthelies.com [Source type: FILTERED WITH BAYES]
.^ When the Voyager II space probe flew past Uranus and Neptune, the apparent north and south magnetic poles were sizably offset from where the rotational pole was in earlier recordings.- A Weakening Magnetic Field and Emerging Sunspot Cycle 24... What Does This Mean for Planet Earth and All Species? | KnowTheLies.com - The Truth is Hidden in Plain View... 13 January 2010 10:13 UTC www.knowthelies.com [Source type: FILTERED WITH BAYES]
^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ But as they were well aware, magnetic north keeps moving, wandering about near the pole as the field gradually changes.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ The electric field at point P is , and the magnetic field is .
^ Today the Earth's magnetic field runs from south to north—which is why compass needles point towards the North Pole—and recent lava flows record a field pointing north.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ The electric field at point P is , and the magnetic field is .
^ (In this way, they resemble the field lines of an iron bar magnet, which arch from the north to the south poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ All matter on Earth assists in creating this field and so becomes charged with this magnetic resonance, displaying different results, dependant on the substance.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ "A general type of mathematical argument is described, which applies to all the cases in which dynamo maintenance of a steady magnetic field by motion in a uniform mass is known to be impossible.- Creation Science and the Earth's MagneticField 13 January 2010 10:13 UTC www.talkorigins.org [Source type: FILTERED WITH BAYES]
^ They suggests that specific tones described as g-mode vibrations are picked up by the magnetic field at the Sun’s surface.- A Weakening Magnetic Field and Emerging Sunspot Cycle 24... What Does This Mean for Planet Earth and All Species? | KnowTheLies.com - The Truth is Hidden in Plain View... 13 January 2010 10:13 UTC www.knowthelies.com [Source type: FILTERED WITH BAYES]
.^ Scientists believe that just as the electric currents produce the magnetic field, so the magnetic field produces the electric currents.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The v oltage on a wire produces electric fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
B-field lines never end
.^ The Russian National Academy of Sciences doesn't give us a time-line, but the change from what was known and accepted to the way it is now represents a 1000 percent increase.- A Weakening Magnetic Field and Emerging Sunspot Cycle 24... What Does This Mean for Planet Earth and All Species? | KnowTheLies.com - The Truth is Hidden in Plain View... 13 January 2010 10:13 UTC www.knowthelies.com [Source type: FILTERED WITH BAYES]
^ A vector going into the page is represented using the tailfeathers of the arrow.
^ (The minus sign simply represents the right-handed relationship of the fields relative to their direction of propagation.
.^ We could, for example, have two solenoidal coils, one in the outgoing line and one in the return line, interwound with one another with their windings oriented so that their differential-mode fields would cancel.
^ In chapter 10 , one of the most important goals was to learn how to calculate the electric field for a given charge distribution.
^ Assume they are long enough to act like ideal solenoids, so that each one only contributes significantly to the field inside itself, and the interior fields are nearly uniform.
.^ The torque on a current loop in a magnetic field.
^ A magnetic field in the form of a sine wave.
^ NARRATOR: As Mars Global Surveyor started to send back data, it soon became clear to Mario and the team that today Mars has no overall magnetic field.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
To date no exception to this rule has been found. (See
magnetic monopole below.)
.^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ (In this way, they resemble the field lines of an iron bar magnet, which arch from the north to the south poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ It appears to orbit, north to south and back to north.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
[11] .^ The electric field at point P is , and the magnetic field is .
^ The bizarre implication was that at some point the entire global magnetic field had done a sudden 180-degree flip, completely reversing direction.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ In the language of space physics, a north-pointing solar magnetic field is called a "northern IMF" and it is synonymous with shields up.- A Weakening Magnetic Field and Emerging Sunspot Cycle 24... What Does This Mean for Planet Earth and All Species? | KnowTheLies.com - The Truth is Hidden in Plain View... 13 January 2010 10:13 UTC www.knowthelies.com [Source type: FILTERED WITH BAYES]
.^ (Recall that the radio beams in an ordinary pulsar come from a rotation-driven outflow of charged particles above the magnetic poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ Suppose, for example, that the axis of the coil is aligned with the magnetic north-south.
^ Today, the magnetic field focuses space radiation towards the far north and south where few people live.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ Two separate physical reasons for a proportionality to length result in an overall proportionality to length squared, which is the same as the area of the loop.
.^ An electric current flowing in a wire or coil produces its own magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ In particular, the fact that electric currents create magnetic fields.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ The magnetic field of a long, straight wire.
.^ Where is the moving charge responsible for this magnetic field?
^ Definition in terms of the force on a moving particle .
^ Likewise, we want to define a magnetic field, B .
.^ Where is the moving charge responsible for this magnetic field?
^ Thus the magnetic field acts like a "bottle," holding charged particles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Modify the calculation on page 617 to determine the component of the magnetic field of a sheet of charge that is perpendicular to the sheet.
.^ GARY GLATZMAIER: Now this movie will show part of a simulation that spans a magnetic field reversal.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ If the velocity vector is initially perpendicular to the field, then the curve of its motion will remain in the plane perpendicular to the field, so the magnitude of the magnetic force on it will stay the same.
^ In the same way I proposed that a magnetic flux field may also comprise particles being the smallest part of the whole field.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
.^ The field must be roughly 10 14 Gauss or more to cause the deep-crust solid to fail.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ In this frame of reference, the earth is moving, and therefore the local magnetic field is changing in strength by 10 -9 T/s.
Magnetic monopole (hypothetical)
.^ Today, the magnetic field focuses space radiation towards the far north and south where few people live.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ (Recall that the radio beams in an ordinary pulsar come from a rotation-driven outflow of charged particles above the magnetic poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Maine The only American state whose name is just one syllable.- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ This buildup of charge would start to quench both currents due to electrical forces, but the current in the right side of the wire, which is driven by the weaker magnetic field, would be the first to stop.
^ From arguments about relative motion, we concluded that moving electric charges create magnetic fields.
.^ Both possibilities are probable, and in either event they would lose their structure as a string and collapse into a field of dissassociated particles, half of which would be manifest as truants.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
^ Diamagnetic materials have the interesting property that they are repelled from regions of strong magnetic field, and it is therefore possible to levitate a diamagnetic object above a magnet, as in figure h .
^ Perhaps some exotic form of matter exists, composed of particles that are magnetic monopoles.
.^ For these admittedly subjective reasons, there have been several searches for magnetic monopoles.
.^ No magnetic monopoles .
^ For these admittedly subjective reasons, there have been several searches for magnetic monopoles.
[12]
In recent research materials known as
spin ices can simulate monopoles, but do not contain actual monopoles.
H-field lines begin and end near magnetic poles
.^ They actually trap in...they record the Earth's magnetic field.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ MARIO ACUNA: So here is my spring, here's my magnet, and if I pass an electrical current through my spring and measure the disturbance of my magnet, which is inside, then I can transmit back to Earth the information about the strength and the direction of the field we are trying to measure.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ So it's really currents inside the Earth's liquid metal core that we think gives rise to the magnetic field.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ This electric field is not created by charges .
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Where is the moving charge responsible for this magnetic field?
.^ In this frame of reference, the earth is moving, and therefore the local magnetic field is changing in strength by 10 -9 T/s.
^ (Recall that the radio beams in an ordinary pulsar come from a rotation-driven outflow of charged particles above the magnetic poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ E 1 = 0 In frame 1, any force experienced by the lone charge must therefore be attributed solely to magnetism.
.^ Determine the electric and magnetic fields.
^ Modify the calculation on page 617 to determine the component of the magnetic field of a sheet of charge that is perpendicular to the sheet.
^ So it's really currents inside the Earth's liquid metal core that we think gives rise to the magnetic field.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
.^ Assume that no other forces are present besides the possible electrical and magnetic ones, and that the fields, if they are present, are uniform.
^ A charged particle of mass m and charge q moves in a circle due to a uniform magnetic field of magnitude B , which points perpendicular to the plane of the circle.
^ The magnetic force on the lone charge q due to the current I is .
)
The magnetic field and electrical currents
.^ This electric field is not created by charges .
^ In particular, the fact that electric currents create magnetic fields.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
Magnetic field due to moving charges and electrical currents
Right hand grip rule: current (
I) flowing through a conductor in the direction indicated by the white arrow produces a magnetic field (
B) around the conductor as shown by the red arrows.
.^ But the nature of the field is evident in all magnetic fields.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
^ Where is the moving charge responsible for this magnetic field?
^ A charged particle is in a region of space in which there is a uniform magnetic field .
[13] .^ The electric field at point P is , and the magnetic field is .
^ When charged particles are moving, they make magnetic fields as well.
^ But magnetism deflects charged particles.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
[14]
.^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ We have a circling atomic current inside the circling current in the wires.
^ What is the magnetic field inside a long, straight wire in which the current density is j ?
.^ In general, determine these plus and minus signs using the right-hand rule shown in the figure.
^ Determine the electric and magnetic fields.
^ If possible, determine the direction of the magnetic or electric field.
.^ Its strength is proportional to the rate at which the field changes.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Milligauss is a unit of flux density , not magnetic field strength, but the difference is not important.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Find the induced magnetic field at a point between the plates, at a distance R from the axis.
[citation needed]
.^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ We have a circling atomic current inside the circling current in the wires.
^ What is the magnetic field inside a long, straight wire in which the current density is j ?
.^ Problem 33 dealt with the dependence of a transformer's gain on the number of loops of wire in the input solenoid.
^ A type of electromagnetic transducer that operates by having a mechanical device move a coil of wire in a magnetic filed to convert the mechanical movement into an electrical current.- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
^ Each coil is made of two sets of 40 turns each of #6 wire wound in rectangular loops, with minimum internal dimensions of 0.86 0.543 m.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ Ultra-strong magnetic fields .- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Scientists have a theory about how the core generates the magnetic field.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ Strong magnetic fields * .- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ Magnetic fields have no sources or sinks.
^ What is the magnetic field inside a long, straight wire in which the current density is j ?
^ Do we have infinite energy in the resulting magnetic field?
.^ Scientists believe that just as the electric currents produce the magnetic field, so the magnetic field produces the electric currents.- NOVA | Transcripts | Magnetic Storm | PBS 13 January 2010 10:13 UTC www.pbs.org [Source type: Original source]
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ In 3, a permanent magnet with double the strength has been used.
[citation needed]
The magnetic field generated by a steady
[15] current I (a constant flow of
charges in which charge is neither accumulating nor depleting at any point) is described by the
Biot–Savart law:
where the integral sums over the entire loop of a wire with
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ If a magnet is dropped on a hard floor, the magnetic field is destroyed because the atoms are "shaken up" and their direction is changed, resulting in a random pattern.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ No significant difference between magnetic field and sham in Trolox-treated animals.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
A slightly more general
[16][17] way of relating the current
I to the B-field is through
Ampère's law:
where the integral is over any arbitrary loop and
Ienc is the current enclosed by that loop.
.^ But we can build just about any static current distribution we like using such a bundle of wires, so it follows that Ampère's law is valid for any static current distribution.
^ Carry out this calculation, using the result for the field of a wire that was established without using Ampère's law.
^ So far, however, we only know how to calculate the magnetic field of a long, straight wire, .
.^ The Φ E equation is Gauss' law: charges make diverging electric fields.
^ What is the velocity of the waves described by Maxwell's equations?
^ The electric field at point P is , and the magnetic field is .
Force due to a B-field on a moving charge
Main article:
Lorentz forceForce on a charged particle
Beam of electrons moving in a circle. Lighting is caused by excitation of atoms of gas in a bulb.
.^ When charged particles are moving, they make magnetic fields as well.
^ Where is the moving charge responsible for this magnetic field?
^ A charged particle is in a region of space in which there is a uniform magnetic field .
This force is known as the
Lorentz force, and is given by
where
.^ This electric field is not created by charges .
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Where is the moving charge responsible for this magnetic field?
.^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The direction of the force is at right angles both to the direction of the magnetic field and the direction of the current.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Suppose a charged particle is moving through a region of space in which there is an electric field perpendicular to its velocity vector, and also a magnetic field perpendicular to both the particle's velocity vector and the electric field.
.^ Where is the moving charge responsible for this magnetic field?
^ Definition in terms of the force on a moving particle .
^ Infer the direction of the magnetic field.
.^ Where is the moving charge responsible for this magnetic field?
^ A charged particle is in a region of space in which there is a uniform magnetic field .
^ When charged particles are moving, they make magnetic fields as well.
.^ Because the other studies reporting effects of magnetic fields on DNA were carried out under continuous exposure conditions, the results of Ivancsits et al.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ No charge will actually flow through the air gap between them, yet a magnetic field will be created in that gap as if the charge were flowing.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ The magnetic force is always perpendicular to the motion of the particle, so it can never do any work, and a charged particle moving through a magnetic field does not experience any change in its kinetic energy: its velocity vector can change its direction, but not its magnitude.
^ However, having said that there is the chance that, at it's worst - it might entertain a purist to see the bazaar machinations of thought applied by an outsider to the complexity of the forces.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
^ Show that there will be one particular velocity at which the particle can be moving that results in a total force of zero on it.
.^ Note that the magnetic field never does work on a charged particle, because its force is perpendicular to the motion; the electric power is actually coming from the mechanical work that had to be done to spin the coil.
^ This electric field is not created by charges .
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
Force on current-carrying wire
Main article:
Laplace force.^ The moving charges in the wire attract the moving charges in the electron beam, causing the electrons to curve.
^ Since the charge densities don't cancel, there is an electric field in frame 2, which points into the wire, attracting the lone charge.
^ This buildup of charge would start to quench both currents due to electrical forces, but the current in the right side of the wire, which is driven by the weaker magnetic field, would be the first to stop.
.^ Find the magnetic force on the wire.
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ What is the magnetic field inside a long, straight wire in which the current density is j ?
.^ There is no induction going on in this frame of reference; the forces that cause the current are just the ordinary magnetic forces experienced by any charged particle moving through a magnetic field.
.^ Where is the moving charge responsible for this magnetic field?
^ By the right-hand rule, the curl points out of the page, i.e., along the positive z axis, so we have .
^ This is in agreement with the right-hand rule.
The force is reversed for a negative charge.
Direction of force
.^ Verify the direction of the force using right-hand rules.
^ This agrees with the right-hand rule.
^ Apply the right-hand rule again to find the direction of wire 2's force on wire 1.
See the figure on the right.
.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Where is the moving charge responsible for this magnetic field?
^ Infer the direction of the magnetic field.
.^ In what direction should the particle be moving in order to minimize the total force acting on it?
^ One solution to this problem relies on the fact that the force experienced by a charged particle in an electric field, F E =q E , is independent of its velocity, but the force due to a magnetic field, F B =q v × B , isn't.
^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
.^ If the velocity vector is initially perpendicular to the field, then the curve of its motion will remain in the plane perpendicular to the field, so the magnitude of the magnetic force on it will stay the same.
^ The following data give the results of two experiments in which charged particles were released from the same point in space, and the forces on them were measured: .
^ Furthermore, reversing the current I in our example would have reversed the force, which would only make sense if the magnetic field had a direction in space that could be reversed.
.^ When charged particles are moving, they make magnetic fields as well.
^ Magnetic fields are supposed to be made by moving charges, but there don't seem to be any moving charges in this landscape.
^ Where is the moving charge responsible for this magnetic field?
.^ We can produce these currents by tiling the region between the circles with square current loops, whose currents all cancel each other except at the inner and outer edges.
^ Now if we're convinced that figure h /2 produces a current in the coil, then it seems very plausible that the same will happen in figure h /1, which implies the existence of induction effects.
^ These metals are called ferromagnetic and their single outer electrons each produce a tiny, circulating current due to the electron orbits.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
)
.^ The relationship between the change in the magnetic field, and the electric field it produces.
^ Geometry of the electric and magnetic fields .
^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Left-handed and right-handed definitions.
^ This is in agreement with the right-hand rule.
^ This agrees with the right-hand rule.
H and B inside and outside of magnetic materials
.^ The torque on a current loop in a magnetic field.
^ Magnetic fields curl around currents.
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
.^ What is the magnetic field inside a long, straight wire in which the current density is j ?
^ The torque on a current loop in a magnetic field.
^ Does the electron experience a magnetic field created by its own current?
.^ The field of a square-loop dipole is very complicated close up, but luckily for us, we only need to know the current at distances that are large compared to the size of the loop, because we're free to make the squares on our grid as small as we like.
^ Electrons flowing in the other direction achieve high velocities, because such lightweight particles are easy to accelerate.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ These metals are called ferromagnetic and their single outer electrons each produce a tiny, circulating current due to the electron orbits.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
)
.^ Likewise, we want to define a magnetic field, B .
^ The current in the first wire creates a magnetic field that acts on the current in the second wire.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The total current is I = I free + I bound , and we define an altered version of the magnetic field, .
Magnetization
Main article:
Magnetization.^ Example 1: The magnetic dipole moment of an atom .
^ Likewise, we want to define a magnetic field, B .
^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
.^ The ambient magnetic field in our laboratory (i.e., when the power supply to the coils was turned off) was 0.14 T. .- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ The distant field of a square dipole turns out to be simple, and is no different from the distant field of any other dipole with the same dipole moment.
^ Ordinary incandescent light bulbs (and electric blankets made since 1992) produce very little magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Example 1: The magnetic dipole moment of an atom .
^ Infer the direction of the magnetic field.
^ A changing electric field can produce a magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ In: 1997 Annual Review of Research on Biological Effects of Electric and Magnetic Fields from the Generation, Delivery, and Use of Electricity.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
^ There is no difference between the “stuff” in one end of the magnet and the other, q .
^ If a charged particle or ion is exposed to a steady magnetic field, it will begin to go into a circular, or orbital motion at right angles to the applied magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Also, as there is no change to the weight of a magnet as a result of this movement of flux then one may conclude that the actual quantity of that flux may be constant.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
^ There is no difference between the “stuff” in one end of the magnet and the other, q .
^ There is, however consensus that there is an ASSUMPTION of an electric field within the material of the magnet.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
)
.^ Magnetic fields have no sources or sinks.
^ Where is the moving charge responsible for this magnetic field?
^ Milligauss is a unit of flux density , not magnetic field strength, but the difference is not important.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ In this frame of reference, every charge has a partner that cancels it, and the net charge everywhere is zero.
^ The horizontal component of the earth's magnetic field varies from zero, at a magnetic pole, to about 10 -4 T near the equator.
.^ Example 1: The magnetic dipole moment of an atom .
^ If the electron is a pointlike particle, then we have an infinite current I through at the moment when it pierces the imaginary surface, and zero current at all other times.
^ This material clearly shows how to build an electric heating device that produces 17 times more heat than the "equivalent" amount of electricity.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
See
#Magnetic dipoles below and magnetic poles vs. atomic currents for more information. The resultant current is called bound current and is the source of the magnetic field due to the magnet. Mathematically, the
curl of
M equals the bound current.
Magnetism
.^ Where is the moving charge responsible for this magnetic field?
^ A changing electric field can produce a magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ MR ( magnetoresistive ) A technology based on the effect where electrical resistance in a material changes when brought in contact with a magnetic field .- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
.^ Where is the moving charge responsible for this magnetic field?
^ So far, however, we only know how to calculate the magnetic field of a long, straight wire, .
^ If the sample is initially unmagnetized, 1, and a field H is externally applied, the magnetization increases, 2, but eventually becomes saturated, 3, so that higher fields do not result in any further magnetization, 4.
.^ Living organisms have the ability to somehow sense these minute daily cycles in the Earth's magnetic field and to use them to time their biological cycles.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ MDM ( modular digital multitrack ) Generic term used to describe any of the families of digital audio multitrack recorders.- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
^ MI ( musical instrument ) A broad term used to describe the musical instrument marketplace in general.- Pro Audio Reference M 13 January 2010 10:13 UTC www.rane.com [Source type: FILTERED WITH BAYES]
Materials are divided into groups based upon their magnetic behavior:
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The relationship between the change in the magnetic field, and the electric field it produces.
^ A changing electric field can produce a magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Diamagnetic materials have the interesting property that they are repelled from regions of strong magnetic field, and it is therefore possible to levitate a diamagnetic object above a magnet, as in figure h .
^ Assume that no other forces are present besides the possible electrical and magnetic ones, and that the fields, if they are present, are uniform.
^ Simultaneously, the magnetic field rearranges itself to a state of lower energy.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
Superconductors often have a broad range of temperatures and magnetic fields (the so named
mixed state) for which they exhibit a complex hysteretic dependence of
M on
B.
H-field and magnetic materials
In the case of paramagnetism, and diamagnetism the magnetization M is often proportional to the applied magnetic field such that:
where
.^ We need to organize our knowledge about the properties that materials can possess, and see whether this knowledge allows us to calculate anything useful with Maxwell's equations.
.^ Consider the configuration where the small one is inside the big one with their currents circulating in the same direction, and a second configuration in which the currents circulate in opposite directions.
^ Describe how a series of measurements with a magnetic compass could be used to determine the strength and direction of its magnetic field at some point of interest.
These relations between
B and
H are examples of
constitutive equations.
.^ However, having said that there is the chance that, at it's worst - it might entertain a purist to see the bazaar machinations of thought applied by an outsider to the complexity of the forces.- Rosemary Ainslie | A Magnetic Field Model 13 January 2010 10:13 UTC www.energeticforum.com [Source type: General]
In all cases, the definition of H given above:
- (definition of H in SI units)
(along with its Gaussian counterpart) is still valid.
.^ Magnetic field significantly different from sham at p < 0.01 in vehicle-treated animals.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ Magnetic field significantly different from sham at p <0.01 in vehicle-treated animals.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
^ No significant difference between magnetic field and sham in 7NI-treated animals.- Magnetic-Field-Induced DNA Strand Breaks in Brain Cells of the Rat 13 January 2010 10:13 UTC ehp03.niehs.nih.gov [Source type: Academic]
.^ The torque on a current loop in a magnetic field.
^ The total current is I = I free + I bound , and we define an altered version of the magnetic field, .
^ The field of any planar current loop can be found by breaking it down into square dipoles.
.^ The magnetic flux through any closed surface is zero.
^ But Gauss' law for magnetism merely says that the magnetic flux through a closed surface is zero.
^ Figure c /3 is closely analogous to figure a /3; in the central gray area, the atomic currents cancel out, but the atoms at the outer surface form a sheet of bound current.
Examining the definition of
H helps flesh out this statement.
Taking the divergence of this definition results in
where the equation has been rearranged so that its parallel to the
displacement field is more obvious.
.^ In other words, the total charge, q , appearing in Maxwell's equartions is actualy q = q free - q bound , where q free is the charge that moves freely through wires, and can be detected in an ammeter, while q bound is the charge bound onto the individual molecules, which can't.
^ Just as an electric dipole contains bound charges, a magnetic dipole has bound currents, which come from the motion of the electrons as they orbit the nucleus, c /1.
^ The total current is I = I free + I bound , and we define an altered version of the magnetic field, .
.^ Where is the moving charge responsible for this magnetic field?
^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ (In this way, they resemble the field lines of an iron bar magnet, which arch from the north to the south poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
Taking the curl of the definition of H yields that:
where
Jf represents the free current.
[24]Energy stored in magnetic fields
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Does the electron experience a magnetic field created by its own current?
^ Magnetic fields curl around currents.
.^ Does the electron experience a magnetic field created by its own current?
^ Magnetic fields curl around currents.
^ The torque on a current loop in a magnetic field.
.^ The current in the first wire creates a magnetic field that acts on the current in the second wire.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ An electric current flowing in a wire or coil produces its own magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Magnetic fields have no sources or sinks.
^ Do we have infinite energy in the resulting magnetic field?
^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
In general the incremental amount of work per unit volume
δW needed to cause a small change of magnetic field
δB is:
If there are no magnetic materials around then we can replace H with B ⁄ μ0,
(Valid only for linear materials with negligible material dispersion)
.^ We need to organize our knowledge about the properties that materials can possess, and see whether this knowledge allows us to calculate anything useful with Maxwell's equations.
^ We then know, for instance, that there cannot be a valid solution to Maxwell's equations in which the same wave pattern moves with double that velocity.
.^ Do we have infinite energy in the resulting magnetic field?
^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Energy in the magnetic field .
Electromagnetism: the relationship between magnetic and electric fields
The magnetic field due to a changing electric field
.^ She observes that a changing magnetic field creates a curly electric field.
^ The relationship between the change in the magnetic field, and the electric field it produces.
^ Geometry of the electric and magnetic fields .
.^ Verify Ampère's law in the case shown in the figure, assuming the known equation for the field of a wire.
^ We have found one specific example of the general law of nature known as Ampère's law: .
^ Unadorned with the ∂Φ E /∂ t term, Maxwell's equation for Γ B reads as c 2 Γ B = 4π k I through , which is Ampère's law.
Therefore the full Ampère's law is:
where
.^ If the particle is pointlike, then it takes zero time to pass any particular location, and the current is then infinite at that point in space.
The last term is Maxwell's correction.
.^ An easy way to approach this is to use the fact that vB has the same units as E , which can be seen by comparing the equations for magnetic and electric forces used above.
^ Modern magnetic therapy is based on traditional ideas, but uses stronger and "out of phase" magnetic materials.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Such an effect is completely inconsistent with the static version of Maxwell's equations; the equations don't even refer to time, so if the magnetic field is changing over time, they will not do anything special.
Electric force due to a changing B-field
.^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ She observes that a changing magnetic field creates a curly electric field.
^ The relationship Γ E ∝ -∂ B /∂ t tells us that a changing magnetic field creates an electric field in the surrounding region of space, but the phrase “surrounding region of space” is vague, and needs to be made mathematical.
.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Where is the moving charge responsible for this magnetic field?
^ Determine the electric and magnetic fields.
.^ X-ray photons traveling through such strong fields readily split into two, or merge together; and many other novel physical effects come into play.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Maxwell convinced himself that light was an electromagnetic wave partly because his equations predicted waves moving at the velocity of light, c .
^ Induction effects like these also lead to the existence of light, which is a wave disturbance in the electric and magnetic fields.
)
.^ This is the basis of power transformers and electric power generation.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ This is known as Faraday's law.
^ We have found one specific example of the general law of nature known as Ampère's law: .
Faraday's law is commonly represented as:
where
.^ The torque on a current loop in a magnetic field.
^ Magnetic fields curl around currents.
^ The magnetic flux through any closed surface is zero.
.^ Both of these fields change over time, however.
^ A changing electric field can produce a magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ As it spins, the nearby magnetic field changes.
A form of Faraday's law of induction that does not include motional EMF is the Maxwell–Faraday equation:
one of
Maxwell's equations.
.^ Such an effect is completely inconsistent with the static version of Maxwell's equations; the equations don't even refer to time, so if the magnetic field is changing over time, they will not do anything special.
^ A complete statement of Maxwell's equations in the presence of electric and magnetic materials is as follows: .
^ The external field can then be reduced, 5, and even eliminated completely, but the material will retain its magnetization.
[25]Maxwell's equations
.^ We find ourselves in a region where the field is very much as it was before, except that all the field vectors have had one unit worth of added to them.
^ Just as a tiny part of a curve looks straight, a tiny part of this magnetic field looks like the field vectors are just getting shorter by the same amount with each step to the right.
^ The clockwise and counterclockwise fields created by the two wires combine by vector addition, and normally cancel out almost exactly.
.^ The Φ E equation is Gauss' law: charges make diverging electric fields.
^ Maxwell's equations for static fields .
^ Dividing these two equations, we find .
.^ A complete statement of Maxwell's equations in the presence of electric and magnetic materials is as follows: .
^ Electric and magnetic forces seem similar in many ways.
^ This buildup of charge would start to quench both currents due to electrical forces, but the current in the right side of the wire, which is driven by the weaker magnetic field, would be the first to stop.
.^ By symmetry, the field in this plane cannot have any component in the radial direction (inward toward the dipole, or outward away from it); it is perpendicular to the plane, and in the opposite direction compared to the dipole vector.
^ The magnetic field vectors lead in paths that loop back on themselves, without ever converging or diverging at a point, as in the fields shown in figure r .
^ For a given AC voltage applied across the inductor, how does the magnetic field depend on N ?
.^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
^ It undoubtedly seems artificial to you that we have discussed dipoles only in the form of a square loop of current.
^ The currents are in opposite directions, and we can imagine them as being joined together at the ends to form a complete circuit, like a tube made of paper that has been squashed almost flat.
This is mathematically equivalent to saying that the
divergence of
B is zero. (Such vector fields are called
solenoidal vector fields.)
.^ No magnetic monopoles .
^ The Φ E equation is Gauss' law: charges make diverging electric fields.
^ Gauss' law in differential form relates , a scalar, to the charge density, another scalar.
.^ The Φ E equation is Gauss' law: charges make diverging electric fields.
^ This electric field is not created by charges .
^ But Ampère's law for electric fields says the curl of E is supposed to be zero.
.^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ What is the magnetic field inside a long, straight wire in which the current density is j ?
^ The torque on a current loop in a magnetic field.
.^ Non-localized fields due to household wiring are usually highest in the room next to where the power line connects or where there is a circuit breaker panel.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ (Of course, magnetic field lines are actually invisible to the eye, but we draw them here so you can see what's happening.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
The position of the wire and its current are (polar) vectors, so they reflect normally. The magnetic field is a pseudovector, so it changes sign when reflected.
.^ Such circulation is called "convection."- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ The increasing magnetic field causes electrons to circulate (current) around the second coil in such a way as to oppose the increasing magnetic field that the first coil is trying to establish.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Because the field is twisted, there is a component of B pointed around the green loop, yielding a non-zero circulation.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
The result of the curl is called a 'circulation source' The curl of
B and of
E are given above and are called the
Ampère–Maxwell equation and
Faraday's law respectively.
The complete set of Maxwell's equations then are:
where
.^ Let's model the current in wire 2 by pretending that there is a line charge inside it, possessing density per unit length λ 2 and moving at velocity v 2 .
.^ This is equivalent to the vector cross product .
^ Momentum, however, is a vector, and there is only one physically meaningful way of multiplying two vectors to get a vector result, which is the cross product (see page 854).
^ As proved on page 854, however, there is only one physically useful way of defining such a multiplication, which is the cross product.
.^ This agrees with the right-hand rule.
^ This is in agreement with the right-hand rule.
^ Momentum, however, is a vector, and there is only one physically meaningful way of multiplying two vectors to get a vector result, which is the cross product (see page 854).
(See diagram to right.)
.^ Shielding magnetic fields is more difficult than shielding electric fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ This electric field is not created by charges .
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
To circumvent this problem the auxiliary
H and
D fields are defined so that Maxwell's equations can be re-factored in terms of the
free current density Jf and
free charge density ρf:
.^ These charged particles readily carry currents.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ These crustal motions generally drive currents outside the star, and generate X-rays.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ (To do this problem, you need to know the relativistic relationship between the energy and momentum of a beam of light.
.^ At all other times (when charges are stable), no current flows.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Now this is very subtle, because Maxwell's equations treat these charges on an equal basis, but in terms of practical measurements, they are completely different.
^ The proportionality to current makes sense, since magnetic forces are interactions between moving charges, and current is a measure of the motion of charge.
Electric and magnetic fields: different aspects of the same phenomenon
.^ In her frame of reference, it's the bar magnet that is moving.
^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
^ But observers in different frames of reference do not agree on simultaneity.
.^ In her frame of reference, it's the bar magnet that is moving.
^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
^ Observers in the two frames agree on how much force there is, so in the loop's frame, we have an electric field .
)
.^ Shielding magnetic fields is more difficult than shielding electric fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Geometry of the electric and magnetic fields .
^ Prove that in an electromagnetic wave, half the energy is in the electric field and half in the magnetic field.
Changing reference frames
mixes these components.
.^ In this way, the energy of a magnetic twist outside a magnetar is gradually dissipated into X-rays.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
Magnetic vector potential
.^ Shielding magnetic fields is more difficult than shielding electric fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Magnetic fields are much more common in the home than are electric fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
In this representation, the
vector potential,
A, and the
scalar potential,
φ, are defined such that:
.^ Let ±λ be the charge per unit length of each line charge without relativistic contraction, i.e., in the frame moving with that line charge.
^ A line charge, with charge per unit length λ, moves at velocity v along its own length.
^ We haven't yet found the proportionality factor that goes in front of the B 2 , but that doesn't matter, because the energy per unit length turns out to be infinite!
.^ Now this is very subtle, because Maxwell's equations treat these charges on an equal basis, but in terms of practical measurements, they are completely different.
^ With the addition of the ∂Φ E /∂ t term, Maxwell's equations are capable of describing electromagnetic waves.
^ Such an effect is completely inconsistent with the static version of Maxwell's equations; the equations don't even refer to time, so if the magnetic field is changing over time, they will not do anything special.
[27] .^ If there wasn't this kind of consistency between the momentum and the energy, then we could violate conservation of momentum by combining light beams or splitting them up.
.^ Also, the use of a power-conditioning outlet strip (specifying reduced electromagnetic interference) is recommended to avoid radio waves being picked up from the power line by the computer.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Even the water bed heater, being farther away from the body, because it is used for several hours at a time, the total administered dose is much higher.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ This configuration has the advantage of being fairly open, so that other apparatus can be easily placed inside and subjected to the field while remaining visible from the outside.
Quantum electrodynamics
.^ Many fascinating physical effects occur in magnetic fields with strength exceeding the "quantum electrodynamic field strength" of B Q = 4.4 X 10 13 Gauss.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ The magnetic field vectors lead in paths that loop back on themselves, without ever converging or diverging at a point, as in the fields shown in figure r .
^ A piezoelectric effect is the creation of an electromagnetic field pulse when a crystalline structure is physically stressed or pushed out of its normal shape.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ The significant increase in these systems and their interactions with other energy fields in our homes, cars and work places will in fact be significantly increasing health risks.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ All electromagnetic fields are force fields, carrying energy and capable of producing an action at a distance.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ All of the possible frequencies of electromagnetic waves or fields can be put onto an electromagnetic spectrum, starting with the slowest frequencies and going to the highest.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
The most accurate modern description of the electromagnetic interaction (and much else) is
Quantum electrodynamics (QED),
[28] which is incorporated into a more complete theory known as the "
Standard Model of particle physics".
.^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
^ Particle-antiparticle pairs are spontaneously created from photons whenever sufficient energy is present.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ The proportionality to current makes sense, since magnetic forces are interactions between moving charges, and current is a measure of the motion of charge.
The magnitude of these interactions is computed using
perturbation theory; these rather complex formulas have a remarkable pictorial representation as
Feynman diagrams.
Predictions of QED agree with experiments to an extremely high degree of accuracy: currently about 10
−12 (and limited by experimental errors); for details see
precision tests of QED.
.^ That wouldn't make sense, because there is no physical reason why one part of the wire would behave differently than any other.
All equations in this article are in the
classical approximation, which is less accurate than the
quantum description as mentioned above. However, under most everyday circumstances, the difference between the two theories is negligible.
Measuring the B-field
.^ The magnetite crystals "tell" the pigeon's brain the exact direction of the Earth's magnetic field, and the pigeon uses this information to navigate with its amazing precision.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ With the advent of such devices as walkie-talkies and mobile phones, it has become apparent that few studies address the consequences of localized exposures to RF fields to the head.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The flow of the electrical currents in the brain produce a magnetic field that can be measured and analyzed several feet away from the head.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
Important classes of magnetometers include using a rotating
coil,
Hall effect magnetometers,
NMR magnetometer,
SQUID magnetometer, and a
fluxgate magnetometer.
.^ Thus the magnetic field acts like a "bottle," holding charged particles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ If a charged particle or ion is exposed to a steady magnetic field, it will begin to go into a circular, or orbital motion at right angles to the applied magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ As the instability grows, the changing, shearing, twisting field drives strong dissipative currents above the star, energizing particles trapped in the exterior magnetic field.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ Occasionally a nearby power line will produce this type of field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The increasing magnetic field causes electrons to circulate (current) around the second coil in such a way as to oppose the increasing magnetic field that the first coil is trying to establish.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Also, the use of a power-conditioning outlet strip (specifying reduced electromagnetic interference) is recommended to avoid radio waves being picked up from the power line by the computer.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ The spatial variation of the magnetic field is on the order of (10 9 T/10 4 m)=10 5 T/m.
^ A changing electric field can produce a magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
[31] .^ (Of course, magnetic field lines are actually invisible to the eye, but we draw them here so you can see what's happening.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ For more information, see my review article, Physics in Ultra-strong Magnetic Fields .- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ In order to act as a "magnet," these atoms must be lined up in the same direction so that the individual magnetic fields combine to produce one big field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
History
One of the first drawings of a magnetic field, by
René Descartes, 1644. It illustrated his theory that magnetism was caused by the circulation of tiny helical particles, "threaded parts", through threaded pores in magnets.
.^ The arrows map the magnetic field B .
^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
^ We, and all other living things, are surrounded by a magnetic field extending out into space from our bodies, and the fields from the brain reflect what is happening in the brain.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Momentum, however, is a vector, and there is only one physically meaningful way of multiplying two vectors to get a vector result, which is the cross product (see page 854).
^ All matter on Earth assists in creating this field and so becomes charged with this magnetic resonance, displaying different results, dependant on the substance.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The core will reach saturation more quickly when the coil's field is in the same direction as the Earth's, but will not saturate as early in the next half-cycle, when the two fields are in opposite directions.
.^ Simultaneously, the magnetic field rearranges itself to a state of lower energy.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Near a neutron star, magnetic field lines are anchored at both ends on the stellar surface, describing arches outside the star.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Occasionally, the magnetic field becomes unstable on much larger scales, and rapidly rearranges itself to a state of lower energy.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
William Gilbert's great work
De Magnete was published in 1600 A.D. and helped to establish the study of magnetism as a science.
.^ But with the advantage of modern hindsight, we can understand in fundamental terms the facts that Faraday had to take simply as mysterious experimental observations.
^ For these reasons, let's look at an alternative method of defining the magnetic field which, although not as fundamental or mathematically simple, may be more appealing.
.^ Observers in the two frames agree on how much force there is, so in the loop's frame, we have an electric field .
^ Since the electric field is curly, an electron can keep gaining more and more energy by circling through it again and again.
^ The core will reach saturation more quickly when the coil's field is in the same direction as the Earth's, but will not saturate as early in the next half-cycle, when the two fields are in opposite directions.
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Find the induced magnetic field at a point between the plates, at a distance R from the axis.
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
.^ A charged particle of mass m and charge q moves in a circle due to a uniform magnetic field of magnitude B , which points perpendicular to the plane of the circle.
^ The magnetic force on the lone charge q due to the current I is .
^ One solution to this problem relies on the fact that the force experienced by a charged particle in an electric field, F E =q E , is independent of its velocity, but the force due to a magnetic field, F B =q v × B , isn't.
.^ This electric field is not created by charges .
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Where is the moving charge responsible for this magnetic field?
.^ This is the same as the field of a magnetic dipole in its midplane, except that the electric coupling constant k replaces the magnetic version k / c 2 , and the electric dipole moment D is substituted for the magnetic dipole moment m .
^ The conventional notation is to incorporate this fudge factor into Gauss's law by defining an altered version of the electric field, .
^ Since some of the fields referred to in Maxwell's equations are the electric and magnetic fields E and B , while others are the auxiliary fields D and H , some of the constraints deal with E and B , others with D and H .
Poisson's model was, unfortunately, incorrect.
.^ A charged particle of mass m and charge q moves in a circle due to a uniform magnetic field of magnitude B , which points perpendicular to the plane of the circle.
^ The magnetic force on the lone charge q due to the current I is .
^ One solution to this problem relies on the fact that the force experienced by a charged particle in an electric field, F E =q E , is independent of its velocity, but the force due to a magnetic field, F B =q v × B , isn't.
.^ This electric field is not created by charges .
^ Where is the moving charge responsible for this magnetic field?
^ Modify the calculation on page 617 to determine the component of the magnetic field of a sheet of charge that is perpendicular to the sheet.
The model, however, was remarkably successful for being fundamentally wrong.
.^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ The relationship between the change in the magnetic field, and the electric field it produces.
^ Although the relationship E ≤ftrightarrow q between electric fields and their sources is unalterably locked in by Gauss's law, that's not what we see in practical measurements.
.^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
^ The proportionality to current makes sense, since magnetic forces are interactions between moving charges, and current is a measure of the motion of charge.
.^ Do we have infinite energy in the resulting magnetic field?
^ Energy in the magnetic field .
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
.^ No charge will actually flow through the air gap between them, yet a magnetic field will be created in that gap as if the charge were flowing.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
^ The proportionality to current makes sense, since magnetic forces are interactions between moving charges, and current is a measure of the motion of charge.
.^ Do we have infinite energy in the resulting magnetic field?
^ Find the increase in the magnetic-field energy, in terms of η, v , and the unknown constant a .
^ Energy in the magnetic field .
.^ Do we have infinite energy in the resulting magnetic field?
^ Energy in the magnetic field .
^ We therefore know that the momentum density of a light beam must depend on a field multiplied by a field.
This is the correct result, but it is derived from an incorrect model.
.^ Geometry of the electric and magnetic fields .
^ What about the field of a magnetic dipole outside of the dipole's midplane?
^ Sunlight, as well as the light from electric lights, is the same thing as the magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Diamagnetic materials have the interesting property that they are repelled from regions of strong magnetic field, and it is therefore possible to levitate a diamagnetic object above a magnet, as in figure h .
^ Therefore the bound currents in a material inserted inside a solenoid tend to reinforce the free currents, and the result is to strengthen the field.
^ E 1 = 0 In frame 1, any force experienced by the lone charge must therefore be attributed solely to magnetism.
.^ Because so many people use cellular telephones, it is important to learn whether RF radiation affects human health, and to provide reassurance if it does not.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Modern magnetic therapy is based on traditional ideas, but uses stronger and "out of phase" magnetic materials.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ But even when the model is physically unrealistic, it still gives the right answers when you use it to compute magnetic effects.
.^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
^ (We could also construct an example like the one in figure c on page 602, in which the field was purely magnetic.
^ We have already seen one example of this on page 554, where we inferred that an inductor's time-varying magnetic field creates an electric field --- an electric field which is not created by any charges anywhere.
.^ Because cancer takes decades to develop, it will be another 10 or 20 years before "mobiles" manifest a bonanza in brain tumors.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ In one case the sources are charges and the field is electric; in the other case we have currents and magnetic fields.
^ If the current is a DC (direct current), the magnetic field is steady, like that form a permanent magnet.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
)
.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ What is the magnetic field inside a long, straight wire in which the current density is j ?
.^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Besides being influenced by a magnetic field, a wire that is carrying a current also produces a magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The current in the first wire creates a magnetic field that acts on the current in the second wire.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Shielding magnetic fields is more difficult than shielding electric fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Magnetic fields are much more common in the home than are electric fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Magnetic fields curl around currents.
.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ From arguments about relative motion, we concluded that moving electric charges create magnetic fields.
^ The charge by itself up above the wire is like a test charge, being used to determine the magnetic and electric fields created by the wire.
.^ The torque on a current loop in a magnetic field.
^ An electric current flowing in a wire or coil produces its own magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ An electric motorized clock, plugged into a wall socket, produces an amazingly high magnetic field because of the small electric motor that runs it.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ She observes that a changing magnetic field creates a curly electric field.
^ The relationship between the change in the magnetic field, and the electric field it produces.
^ Geometry of the electric and magnetic fields .
.^ James Clerk Maxwell (1831-1879) .
^ This observer also predicts that the particles will collide, but explains their motion in terms of both an electric field, E , and a magnetic field, B .
^ This whole line of reasoning was not available to Faraday and his contemporaries, since they thought the relative nature of motion only applied to matter, not to electric and magnetic fields.
.^ A diffuse flux of such particles rains down on the Earth all the time, from the depths of space.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ When the magnetic forces get strong enough, they can also yield to the magnetic stress and move "plastically," truly changing the crust's structure.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Moreover, if magnetic twists (and currents) extend out far from the star, to regions where outgoing magnetic waves are generated due to the stellar rotation, then they will affect the rate at which the star spins down.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
^ The proportionality to current makes sense, since magnetic forces are interactions between moving charges, and current is a measure of the motion of charge.
.^ If the velocity vector is initially perpendicular to the field, then the curve of its motion will remain in the plane perpendicular to the field, so the magnitude of the magnetic force on it will stay the same.
^ Magnetic forces are forces between moving charges and other moving charges, so a magnetic field can never accelerate a charged particle starting from rest.
^ The proportionality to current makes sense, since magnetic forces are interactions between moving charges, and current is a measure of the motion of charge.
.^ To satisfy Maxwell's equations, the time derivatives of the fields must also be twice as large for the blue light.
^ The fluxgate compass is a type of magnetic compass without moving parts, commonly used on ships and aircraft.
^ We need to organize our knowledge about the properties that materials can possess, and see whether this knowledge allows us to calculate anything useful with Maxwell's equations.
This quantity was therefore a measure of the vorticity in the magnetic lines of force, and Maxwell referred to it as the intensity of the magnetic force.
.^ If the dimensions of the cross-sectional square (height and front-to-back) are b , find the magnetic field (magnitude and direction) along the long central axis.
^ With electricity, it turned out to be useful to define an electric field rather than always working in terms of electric forces.
^ In section 10.4 , I've already argued that the energy density of the magnetic field must be proportional to .
.^ We can also anticipate that the magnetic field will be a vector.
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
.^ Now this is very subtle, because Maxwell's equations treat these charges on an equal basis, but in terms of practical measurements, they are completely different.
^ Such an effect is completely inconsistent with the static version of Maxwell's equations; the equations don't even refer to time, so if the magnetic field is changing over time, they will not do anything special.
^ A complete statement of Maxwell's equations in the presence of electric and magnetic materials is as follows: .
.^ In her frame of reference, it's the bar magnet that is moving.
^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
^ Geometry of the electric and magnetic fields .
Finally, the emergent field of
quantum mechanics was merged with electrodynamics to form
quantum electrodynamics or QED.
.^ From arguments about relative motion, we concluded that moving electric charges create magnetic fields.
^ In the frame of reference where the loop is moving, a charge q moving along with the loop at velocity v will experience a magnetic force .
^ The protons and electrons in the coil are moving through a magnetic field, so they experience forces.
This thought experiment revolves around the interpretation of
Faraday's law, as explained next:
.^ One loop is in the y - z plane, the other in the x - y plane.
^ A different observer, a /2, says the particles are moving.
^ Observers in the two frames agree on how much force there is, so in the loop's frame, we have an electric field .
.^ Momentum, however, is a vector, and there is only one physically meaningful way of multiplying two vectors to get a vector result, which is the cross product (see page 854).
^ The two processes are supposed to use completely different waves of energy and at different intensities.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Two separate physical reasons for a proportionality to length result in an overall proportionality to length squared, which is the same as the area of the loop.
.^ Where is the moving charge responsible for this magnetic field?
^ The torque on a current loop in a magnetic field.
^ A permanent magnetic field is stationary or still, unless you are moving the magnet.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Magnetic fields have no sources or sinks.
^ In this frame of reference, the earth is moving, and therefore the local magnetic field is changing in strength by 10 -9 T/s.
^ Where is the moving charge responsible for this magnetic field?
.^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ An AC electric field will also create a current in the body.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The magnetic field, in turn, creates an electric field, which reinforces the existing electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Where is the moving charge responsible for this magnetic field?
^ From arguments about relative motion, we concluded that moving electric charges create magnetic fields.
See
Faraday's law as two different phenomena. Einstein, on the other hand, proposed the equivalence of these two scenarios
[32] in the first postulate of relativity that the physics depends on only
relative motion.
.^ A charged particle and a current, seen in two different frames of reference.
^ The pair of charged particles, as seen in two different frames of reference.
^ In this frame of reference, the earth is moving, and therefore the local magnetic field is changing in strength by 10 -9 T/s.
Likewise, the same is true of
E and
B, which are not separate, but are aspects of the same
electromagnetic tensor.
Important uses and examples of magnetic field
Magnetic circuits
.^ If a current of 1.0 A is used, find the magnetic field inside the solenoid if the core is air, and if the core is made of iron with μ/μ o =4,000.
.^ Here are the magnetic permeabilities of some substances: .
^ The result is that when a magnetic field enters a high-permeability material, it tends to twist abruptly to one side, and the pattern of the field tends to be channeled through the material like water through a funnel.
^ A magnetically permeable material is placed at the center of a solenoid.
.^ The Φ E equation is Gauss' law: charges make diverging electric fields.
^ The small arrows show the result of the Biot-Savart law at various positions relative to the current segment .
^ Gauss' law in differential form relates , a scalar, to the charge density, another scalar.
Extending this analogy we derive the counterpart to the macroscopic Ohm's law (
I = V ⁄ R ) as:
where
is the magnetic flux in the circuit,
is the
magnetomotive force applied to the circuit, and
Rm is the
reluctance of the circuit. Here the reluctance
Rm is a quantity similar in nature to
resistance for the flux.
.^ Geometry of the electric and magnetic fields .
^ The magnetic field of a long, straight wire.
^ Modify the calculation on page 617 to determine the component of the magnetic field of a sheet of charge that is perpendicular to the sheet.
Hall effect
Main article:
Hall effect.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ Where is the moving charge responsible for this magnetic field?
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Infer the direction of the magnetic field.
^ Do we have infinite energy in the resulting magnetic field?
^ The current is at right angles to the direction of the changing magnetic field, and is strongest near the extremities of a person.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
This is known as the
Hall effect.
.^ When a field is curly, we can measure its curliness using a circulation.
^ Effects like magnetic photon splitting cannot be measured in terrestrial laboratories, but may be detected in emissions from these unique cosmic laboratores.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
.^ Positive and negative signs in Ampère's law.
^ Positive and negative signs .
^ These lodestones have been charged by the Earth, and thus are harmoniously in tune with the human bodies' frequencies as well, they have for thousands of years been successfully used in the healing arts.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
Magnetic field shape descriptions
.^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ (In this way, they resemble the field lines of an iron bar magnet, which arch from the north to the south poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.
- An azimuthal magnetic field is one that runs east-west.
- A meridional magnetic field is one that runs north-south.^ That is, it is not a simple field with just a north and south pole, like a bar magnet.
- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
.^ Dynamos operate in the interior of the Earth and the Sun, giving them their magnetic fields.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ An electric motorized clock, plugged into a wall socket, produces an amazingly high magnetic field because of the small electric motor that runs it.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The changing magnetic field creates an electric field directly in the wire, which causes electrons in the wire to move.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
The reverse process is called the alpha-effect.[33]
.
- A quadrupole magnetic field is one seen, for example, between the poles of four bar magnets.^ Where is the moving charge responsible for this magnetic field?
^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
^ A charged particle is in a region of space in which there is a uniform magnetic field .
.
- A solenoidal magnetic field is similar to a dipole magnetic field, except that a solid bar magnet is replaced by a hollow electromagnetic coil magnet.
- A toroidal magnetic field occurs in a doughnut-shaped coil, the electric current spiraling around the tube-like surface, and is found, for example, in a tokamak.
- A poloidal magnetic field is generated by a current flowing in a ring, and is found, for example, in a tokamak.
- A radial magnetic field is one in which the field lines are directed from the center outwards, similar to the spokes in a bicycle wheel.^ If the current is a DC (direct current), the magnetic field is steady, like that form a permanent magnet.
- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Or an example where the fields are purely electric in one frame, but purely magnetic in another?
^ Example 1: The magnetic dipole moment of an atom .
An example can be found in a loudspeaker transducers (driver).[34]
.
- A helical magnetic field is corkscrew-shaped, and sometimes seen in space plasmas such as the Orion Molecular Cloud.^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.
- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ A charged particle is in a region of space in which there is a uniform magnetic field .
^ Such a substance, subjected to a magnetic field, tends to align itself, c /2, so that a sheet of current circulates around the externally applied field.
[35]
Magnetic dipoles
Magnetic field lines around a ”magnetostatic dipole” pointing to the right.
.^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
^ The current is at right angles to the direction of the changing magnetic field, and is strongest near the extremities of a person.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The magnetic field pattern around a bar magnet is created by the superposition of the dipole fields of the individual iron atoms.
.^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
^ This is the same as the field of a magnetic dipole in its midplane, except that the electric coupling constant k replaces the magnetic version k / c 2 , and the electric dipole moment D is substituted for the magnetic dipole moment m .
^ An easy way to approach this is to use the fact that vB has the same units as E , which can be seen by comparing the equations for magnetic and electric forces used above.
.^ The torque on a current loop in a magnetic field.
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ An electric dipole, unlike a magnetic one, can be built out of two opposite monopoles, i.e., charges, separated by a certain distance, and it is then straightforward to show by vector addition that the field of an electric dipole is .
Such a current loop has a magnetic moment of:
where the direction of
.^ This is in agreement with the right-hand rule.
^ Verify the direction of the force using right-hand rules.
^ This agrees with the right-hand rule.
.^ Such a substance, subjected to a magnetic field, tends to align itself, c /2, so that a sheet of current circulates around the externally applied field.
^ Apparently, nearly all the atoms in such a magnet are oriented randomly, and do not contribute to the magnet's dipole moment.
^ The increasing magnetic field causes electrons to circulate (current) around the second coil in such a way as to oppose the increasing magnetic field that the first coil is trying to establish.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Example 1: The magnetic dipole moment of an atom .
^ The s state, for example, has zero angular momentum.
^ Suppose the currents are in the same direction.
.^ An electric dipole, unlike a magnetic one, can be built out of two opposite monopoles, i.e., charges, separated by a certain distance, and it is then straightforward to show by vector addition that the field of an electric dipole is .
^ In one case the sources are charges and the field is electric; in the other case we have currents and magnetic fields.
^ Roughly speaking, it looks like the field of one big dipole, especially farther away from the magnet.
This model produces an
H-field not a
B-field.
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ No charge will actually flow through the air gap between them, yet a magnetic field will be created in that gap as if the charge were flowing.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ If the braking was due to magnetic waves carrying away energy and angular momentum, as seemed plausible, then the field strength was 8 X 10 14 Gauss.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Magnetism, as we discussed previously, is an interaction between a moving charge and another moving charge, as opposed to electric forces, which act between any pair of charges, regardless of their motion.
Earth's magnetic field
.^ Magnetic fields have no sources or sinks.
^ Living organisms have the ability to somehow sense these minute daily cycles in the Earth's magnetic field and to use them to time their biological cycles.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The magnetite crystals "tell" the pigeon's brain the exact direction of the Earth's magnetic field, and the pigeon uses this information to navigate with its amazing precision.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Since the distance from the equator to a pole is about 10 7 m, we can estimate, very roughly, that the horizontal component of the earth's magnetic field typically varies by about 10 -11 T/m as you go north or south.
^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ (In this way, they resemble the field lines of an iron bar magnet, which arch from the north to the south poles.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ Since the distance from the equator to a pole is about 10 7 m, we can estimate, very roughly, that the horizontal component of the earth's magnetic field typically varies by about 10 -11 T/m as you go north or south.
^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ For example, magnetic field lines continually drift through the star's liquid interior, stressing the crust from below.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
Earth's magnetic field is produced in the outer liquid part of its core due to a
dynamo that produce electrical currents there.
.^ The Earths magnetic field, which deflects compass needles .- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ The electric field at point P is , and the magnetic field is .
^ Upon detecting a GRB, Swift swiftly (within 20-70 seconds) turns and points both an X-ray telescope and an optical-UV telescope toward it.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ You manage to learn quite a bit of each other's languages, but you're stumped when you try to establish the definitions of left and right (or, equivalently, clockwise and counterclockwise).
^ Assume that no other forces are present besides the possible electrical and magnetic ones, and that the fields, if they are present, are uniform.
^ That is, it is not a simple field with just a north and south pole, like a bar magnet.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ Suppose, for example, that the axis of the coil is aligned with the magnetic north-south.
^ The compasses in the chain are stable when aligned with one another, because each one's north end is attracted to its neighbor's south end.
^ The aliens might have reversed their definition of the magnetic field, in which case their drawings of field patterns would look like mirror images of ours, as in the left panel of figure t .
[37] .^ Suppose, for example, that the axis of the coil is aligned with the magnetic north-south.
^ The compasses in the chain are stable when aligned with one another, because each one's north end is attracted to its neighbor's south end.
^ The horizontal component of the earth's magnetic field varies from zero, at a magnetic pole, to about 10 -4 T near the equator.
)
.^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ This is because the current in the coil sets up its own magnetic field, and that field exerts a torque on the magnet.
^ A charged particle is in a region of space in which there is a uniform magnetic field .
.^ The current is at right angles to the direction of the changing magnetic field, and is strongest near the extremities of a person.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ The magnetite crystals "tell" the pigeon's brain the exact direction of the Earth's magnetic field, and the pigeon uses this information to navigate with its amazing precision.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ In this frame of reference, the earth is moving, and therefore the local magnetic field is changing in strength by 10 -9 T/s.
.^ Suppose, for example, that the axis of the coil is aligned with the magnetic north-south.
^ Modify the calculation on page 617 to determine the component of the magnetic field of a sheet of charge that is perpendicular to the sheet.
^ Their magnetic fields could sweep up diffuse gas from interstellar space, helping to make dead magnetars glow.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
.^ Since the distance from the equator to a pole is about 10 7 m, we can estimate, very roughly, that the horizontal component of the earth's magnetic field typically varies by about 10 -11 T/m as you go north or south.
^ The horizontal component of the earth's magnetic field varies from zero, at a magnetic pole, to about 10 -4 T near the equator.
)
.^ Dynamos operate in the interior of the Earth and the Sun, giving them their magnetic fields.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ A current will not flow through a resistor unless there is some electric field pushing the electrons, so we conclude that the changing magnetic field has produced an electric field in the surrounding space.
^ There are three types of energy involved: the increase in the magnetic field energy, the increase in the energy of the outside world, and the decrease in energy as the battery is drained.
.^ The electric field of a sheet of charge, and the magnetic field of a sheet of current.
^ The relationship between the change in the magnetic field, and the electric field it produces.
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ The strength of the Earth's magnetic field averages about half a gauss.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ (This field-strength given by a combination of fundamental constants: B Q = m e 2 c 3 / h e , where m e is the mass of the electron, c is the speed of light, h is Planck's constant divided by 2 π, and e is the charge on an electron.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
The poles even periodically reverse direction, in a process called
geomagnetic reversal.
Rotating magnetic fields
.^ Magnetic fields curl around currents.
^ The torque on a current loop in a magnetic field.
^ An electric current flowing in a wire or coil produces its own magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ Because the hysteresis curve is highly nonlinear, the addition of an external field such as the Earth's alters the core's behavior.
^ If the current is a DC (direct current), the magnetic field is steady, like that form a permanent magnet.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ An AC electric field will also create a current in the body.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Electric current in your home is supposed to flow out of one side of the outlet, through an appliance, and back into the wall through the other side of the outlet.
.^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Any wire that carries an AC electrical current produces magnetic fields.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Magnetic fields curl around currents.
.^ A large current flows through the wire.
^ Four long wires are arranged, as shown, so that their cross-section forms a square, with connections at the ends so that current flows through all four before exiting.
^ A wire carrying current I passes perpendicularly through the center of the rectangular Ampèrian surface.
.^ Relate λ 2 and v 2 to the current I 2 , using the result of problem 5 a.
^ The magnitude of this force equals (homework problem 6 ), and using the definition of force, d p /d t , we find for the magnitude of the momentum transferred: .
^ For a given emf applied by an external radio wave, the current induced in the circuit has been attenuated by an order of magnitude, relative to its value without the ferrite bead.
.^ The coil on the input side creates a magnetic field.
^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ An electric current flowing in a wire or coil produces its own magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ This electric field is not created by charges .
^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ In reception, both conductors are bathed in the same electric and magnetic fields, so an emf that adds current on one side subtracts current from the other side, resulting in cancellation.
.^ Now perhaps we can use reasoning with the same flavor to show that changing magnetic fields produce curly electric fields.
^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ This is because the current in the coil sets up its own magnetic field, and that field exerts a torque on the magnet.
.^ Magnetic fields are produced by moving electrical currents, and the field of a bar magnet is produced by the spinning electrons around the atomic nuclei in the iron material of the magnet itself.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ Since the magnetic field lines were anchored to the rotating neutron star, the zones of glowing gas also turned every 8 seconds.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ For these currents induced by magnetic fields, the current per area increases proportional to the linear size of the organism.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
.^ A radio pulsar's magnetic field is essentially stable; its main role is to passively facilitate the loss of rotational energy.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ The unit of magnetic field, the tesla, is named after Serbian-American inventor Nikola Tesla.
^ Since the magnetic field lines were anchored to the rotating neutron star, the zones of glowing gas also turned every 8 seconds.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
In 1885,
Galileo Ferraris independently researched the concept. In 1888, Tesla gained
U.S. Patent 381,968 for his work. Also in 1888, Ferraris published his research in a paper to the
Royal Academy of Sciences in
Turin.
See also
General
Mathematics
- Ampère's law – law describing how currents act as circulation sources for magnetic fields.
- Biot–Savart law – the magnetic field set up by a steadily flowing line current.
- Magnetic helicity – extent to which a magnetic field "wraps around itself".
- Maxwell's equations – four equations describing the behavior of electric and magnetic fields and their interaction with matter.
Applications
Notes and references
- ^ Technically, magnetic field is a pseudo vector; pseudo-vectors, which also include torque and rotational velocity, are similar to vectors except that they remain unchanged when the coordinates are inverted.
- ^ The standard graduate textbook by J. D. Jackson "Classical Electrodynamics" specifically follows the historical tradition, specifically, "In the presence of magnetic materials the dipole tends to align itself in a certain direction. That direction is by definition the direction of the magnetic flux density, denoted by B, provided the dipole is sufficiently small and weak that it does not perturb the existing field". Similarly, in Section 5 of Jackson, H is referred to as the magnetic field. Hence, Edward Purcell, in Electricity and Magnetism, McGraw-Hill, 1963, writes, Even some modern writers who treat B as the primary field feel obliged to call it the magnetic induction because the name magnetic field was historically preempted by H. This seems clumsy and pedantic. If you go into the laboratory and ask a physicist what causes the pion trajectories in his bubble chamber to curve, he'll probably answer "magnetic field", not "magnetic induction." You will seldom hear a geophysicist refer to the Earth's magnetic induction, or an astrophysicist talk about the magnetic induction of the galaxy. We propose to keep on calling B the magnetic field. As for H, although other names have been invented for it, we shall call it "the field H" or even "the magnetic field H." In a similar vein, M Gerloch (1983). Magnetism and Ligand-field Analysis. Cambridge University Press. p. 110. ISBN 0521249392. http://books.google.com/books?id=Ovo8AAAAIAAJ&pg=PA110. says: “So we may think of both B and H as magnetic fields, but drop the word 'magnetic' from H so as to maintain the distinction … As Purcell points out, 'it is only the names that give trouble, not the symbols'.”
- ^ R. Nave (2005). "Magnetic Field Strength H". HyperPhysics. Georgia State University, Deptartement of Physics and Astronomy. http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfield.html.
- ^ Magnetic Field Strength Converter, UnitConversion.org.
- ^ H. P. Myers (1997). Introductory solid state physics (2nd ed.). Taylor & Francis. p. 366. ISBN 074840659X. http://books.google.com/books?id=QhqyWH7DDQ0C&pg=PA366.
- ^ Yuval Ne ̕eman, Y. Kirsh (1996). The Particle Hunters (2 ed.). Cambridge University Press. p. 56. ISBN 0521476860. http://books.google.com/books?id=K4jcfCguj8YC&pg=PA56.
- ^ John S Townsend (2000). "Stern–Gerlach experiments". A Modern Approach to Quantum Mechanics (2 ed.). University Science Books. pp. 1–23. ISBN 1891389130. http://books.google.com/books?id=3_7uriPX028C&pg=PA3.
- ^ See Eq. 11.42 in E. Richard Cohen, David R. Lide, George L. Trigg (2003). AIP physics desk reference (3 ed.). Birkhäuser. p. 381. ISBN 0387989730. http://books.google.com/books?id=JStYf6WlXpgC&pg=PA381.
- ^ Griffiths, David J. (1999). .^ Introduction to Electrodynamics (3rd ed.
- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
- PowerPedia:Magnetic field - PESWiki 13 January 2010 10:13 UTC peswiki.com [Source type: Academic]
^ Classical Electrodynamics (3rd ed.- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
- PowerPedia:Magnetic field - PESWiki 13 January 2010 10:13 UTC peswiki.com [Source type: Academic]
). Prentice Hall. pp. 255–8. ISBN 0-13-805326-X. OCLC 40251748.
- ^ The use of iron filings to display a field presents something of an exception to this picture; the filing alter the magnetic field so that it is much larger along the "lines" of iron, due to the large permeability of iron relative to air.
- ^ To see that this must be true imagine placing a compass inside a magnet. There, the north pole of the compass will point toward the north pole of the magnet since magnets stacked on each other point in the same direction.
- ^ Two experiments produced candidate events that were initially interpreted as monopoles, but these are now regarded to be inconclusive. For details and references, see magnetic monopole.
- ^ In special relativity this means that electric and magnetic fields are two parts of the same phenomenon, for a moving charge produces both an electric and a magnetic field. But in a reference frame where the particle is not moving, there is only an electric field. However, the same physics applies to all reference systems. In this reference system, the electric field changes as well to produces the same force as the original reference frame. It is probably a mistake, however, to say that the electric field causes the magnetic field when relativity is taken into account, since relativity favors no particular reference frame. (One could just as easily say that the magnetic field caused an electric field.) More importantly, it is not always possible to move into a coordinate system in which all of the charges are stationary. See classical electromagnetism and special relativity.[citation needed]
- ^ Griffiths, David J. (1999). Introduction to Electrodynamics (3rd ed.). Prentice Hall. p. 438. ISBN 0-13-805326-X. OCLC 40251748.
- ^ In practice the Biot–Savart law and other laws of magnetostatics can often be used even when the charge is changing in time as long as it is not changing too quickly. This situation is known as being quasistatic.[citation needed]
- ^ Griffiths, David J. (1999). Introduction to Electrodynamics (3rd ed.). Prentice Hall. pp. 222–225. ISBN 0-13-805326-X. OCLC 40251748.
- ^ The Biot–Savart law contains the additional restriction (boundary condition) that the B-field must go to zero fast enough at infinity. It also depends on the divergence of B being zero, which is always valid. (There are no magnetic charges.)
- ^ Deissler, R.J. (2008). "Dipole in a magnetic field, work, and quantum spin". Physical Review E 77 (3, pt 2): 036609. doi:10.1103/PhysRevE.77.036609. PMID 18517545. http://academic.csuohio.edu/deissler/PhysRevE_77_036609.pdf.
- ^ a b RJD Tilley (2004). Understanding Solids. Wiley. p. 368. ISBN 0470852755. http://books.google.com/books?id=ZVgOLCXNoMoC&pg=PA368.
- ^ Sōshin Chikazumi, Chad D. Graham (1997). Physics of ferromagnetism (2 ed.). Oxford University Press. p. 118. ISBN 0198517769. http://books.google.com/books?id=AZVfuxXF2GsC&printsec=frontcover.
- ^ Amikam Aharoni (2000). Introduction to the theory of ferromagnetism (2 ed.). Oxford University Press. p. 27. ISBN 0198508085. http://books.google.com/books?id=9RvNuIDh0qMC&pg=PA27.
- ^ M Brian Maple et al. (2008). "Unconventional superconductivity in novel materials". in K. H. Bennemann, John B. Ketterson. Superconductivity. Springer. p. 640. ISBN 3540732527. http://books.google.com/books?id=PguAgEQTiQwC&pg=PA640.
- ^ Naoum Karchev (2003). "Itinerant ferromagnetism and superconductivity". in Paul S. Lewis, D. Di (CON) Castro. Superconductivity research at the leading edge. Nova Publishers. p. 169. ISBN 1590338618. http://books.google.com/books?id=3AFo_yxBkD0C&pg=PA169.
- ^ John Clarke Slater, Nathaniel Herman Frank (1969). Electromagnetism (first published in 1947 ed.). Courier Dover Publications. p. 69. ISBN 0486622630. http://books.google.com/books?id=GYsphnFwUuUC&pg=PA69.
- ^ A complete expression for Faraday's law of induction in terms of the electric E and magnetic fields can be written as:
where ∂Σ(t) is the moving closed path bounding the moving surface Σ(t), and dA is an element of surface area of Σ(t). The first integral calculates the work done moving a charge a distance dℓ based upon the Lorentz force law. In the case where the bounding surface is stationary, the Kelvin–Stokes theorem can be used to show this equation is equivalent to the Maxwell–Faraday equation.
- ^ E. J. Konopinski (1978). "What the electromagnetic vector potential describes". Am. J. Phys. 46 (5): 499–502. doi:10.1119/1.11298.
- ^ Griffiths, David J. (1999). .^ Introduction to Electrodynamics (3rd ed.
- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
- PowerPedia:Magnetic field - PESWiki 13 January 2010 10:13 UTC peswiki.com [Source type: Academic]
^ Classical Electrodynamics (3rd ed.- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
- PowerPedia:Magnetic field - PESWiki 13 January 2010 10:13 UTC peswiki.com [Source type: Academic]
). Prentice Hall. p. 422. ISBN 0-13-805326-X. OCLC 40251748.
- ^ For a good qualitative introduction see: Feynman, Richard (2006). QED: the strange theory of light and matter. Princeton University Press. ISBN 0-691-12575-9.
- ^ [1] Gravity Probe B
- ^ "With record magnetic fields to the 21st Century". IEEE Xplore. http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=823621.
- ^ Kouveliotou, C.; Duncan, R. C.; Thompson, C. (February 2003). "Magnetars". Scientific American; Page 36.
- ^ Einstein, Albert (1905). "Zur Elektrodynamik bewegter Körper (On the Electrodynamics of Moving Bodies)". Annalen der Physik (17): 891–921. http://www.fourmilab.ch/etexts/einstein/specrel/www/. Retrieved 2009-06-18. "They suggest rather that, as has already been shown to the first order of small quantities, the same laws of electrodynamics and optics will be valid for all frames of reference for which the equations of mechanics hold good.1 We will raise this conjecture (the purport of which will hereafter be called the “Principle of Relativity”).".
- ^ The Solar Dynamo, retrieved Sep 15, 2007.
- ^ I. S. Falconer and M. I. Large (edited by I. M. Sefton), "Magnetism: Fields and Forces" Lecture E6, The University of Sydney, retrieved 3 Oct 2008
- ^ Robert Sanders, "Astronomers find magnetic Slinky in Orion", 12 January 2006 at UC Berkeley. Retrieved 3 Oct 2008
- ^ (See magnetic moment for further information.) B. D. Cullity, C. D. Graham (2008). Introduction to Magnetic Materials (2 ed.). Wiley-IEEE. p. 103. ISBN 0471477419. http://books.google.com/books?id=ixAe4qIGEmwC&pg=PA103.
- ^ College Physics, Volume 10, by Serway, Vuille, and Faughn, page 628 weblink. "the geographic North Pole of Earth corresponds to a magnetic south pole, and the geographic South Pole of Earth corresponds to a magnetic north pole".
Further reading
Web
- Nave, R.. .. Retrieved 2007-06-04.
- Oppelt, Arnulf (2006-11-02). .. ..
- "magnetic field strength converter".^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.
- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ In this frame of reference, the earth is moving, and therefore the local magnetic field is changing in strength by 10 -9 T/s.
^ Compute and , and compare with the strengths of static fields you experience in everyday life: E ∼ 10 6 V/m in a thunderstorm, and B ∼ 10 -3 T for the Earth's magnetic field.
..^ Physicists have not made steady fields stronger than 4.5 x 10 5 Gauss in the lab because the magnetic stresses of such fields exceed the tensile strength of terrestrial materials.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ In this frame of reference, the earth is moving, and therefore the local magnetic field is changing in strength by 10 -9 T/s.
^ Compute and , and compare with the strengths of static fields you experience in everyday life: E ∼ 10 6 V/m in a thunderstorm, and B ∼ 10 -3 T for the Earth's magnetic field.
Retrieved 2007-06-04.
Books
- Durney, Carl H. and Johnson, Curtis C. (1969). Introduction to modern electromagnetics. McGraw-Hill. ISBN 0-07-018388-0.
- Griffiths, David J. (1999). .^ Introduction to Electrodynamics (3rd ed.
- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
- PowerPedia:Magnetic field - PESWiki 13 January 2010 10:13 UTC peswiki.com [Source type: Academic]
^ Classical Electrodynamics (3rd ed.- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
- PowerPedia:Magnetic field - PESWiki 13 January 2010 10:13 UTC peswiki.com [Source type: Academic]
). Prentice Hall. ISBN 0-13-805326-X. OCLC 40251748.
- Jackson, John D. (1999). .^ Introduction to Electrodynamics (3rd ed.
- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
^ Classical Electrodynamics (3rd ed.- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
). Wiley. ISBN 0-471-30932-X. OCLC 224523909.
- Tipler, Paul (2004). .^ Physics for Scientists and Engineers: Electricity, Magnetism, Light, and Elementary Modern Physics (5th ed.
- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
- PowerPedia:Magnetic field - PESWiki 13 January 2010 10:13 UTC peswiki.com [Source type: Academic]
^ Magnetic field lines shown by iron filings In physics , the magnetic field is a field that permeates space and which exerts a magnetic force on moving electric charges and magnetic dipoles .- Magnetic Field K-12 Experiments for Lesson Plans & Science Fair Projects 13 January 2010 10:13 UTC www.juliantrubin.com [Source type: Academic]
^ Ordinary incandescent light bulbs (and electric blankets made since 1992) produce very little magnetic field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
). W. H. Freeman. ISBN 0-7167-0810-8. OCLC 51095685.
- Furlani, Edward P. (2001). Permanent Magnet and Electromechanical Devices: Materials, Analysis and Applications. Academic Press Series in Electromagnetism. ISBN 0-12-269951-3. OCLC 162129430.
External links
Information
.^ Electromagnetic waves are supposed to have their electric and magnetic fields perpendicular to each other.
^ However, the electromagnetic wave also has a magnetic field, and a magnetic field transfers momentum to (exerts a force on) a current.
^ In terms of transmission, the magnetic field created by the outgoing current is almost exactly canceled by the field from the return current, so electromagnetic waves are only weakly induced.
theory.uwinnipeg.ca.
Field density
- Jiles, David (1994). Introduction to Electronic Properties of Materials (1st ed.). Springer. ISBN 0-412-49580-5.
Rotating magnetic fields
.^ An electric motorized clock, plugged into a wall socket, produces an amazingly high magnetic field because of the small electric motor that runs it.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ A radio pulsar's magnetic field is essentially stable; its main role is to passively facilitate the loss of rotational energy.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
^ A basic generator, f , consists of a permanent magnet that rotates within a coil of wire.
Integrated Publishing.
Diagrams
.^ Geometry of the electric and magnetic fields .
^ A changing magnetic field can create an electric field.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ What is the difference between an electric field and a magnetic field?- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
eng.ox.ac.uk.
.^ An electric motorized clock, plugged into a wall socket, produces an amazingly high magnetic field because of the small electric motor that runs it.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
^ However, the magnetic field patterns shown in figure s seems to violate this principle.
^ A radio pulsar's magnetic field is essentially stable; its main role is to passively facilitate the loss of rotational energy.- `MAGNETARS', SOFT GAMMA REPEATERS & VERY STRONG MAGNETIC FIELDS Robert C. Duncan, University of Texas at Austin 13 January 2010 10:13 UTC solomon.as.utexas.edu [Source type: General]
Integrated Publishing.
Journal Articles
.^ As we'll see shortly, the magnetic field is required in order to maintain consistency between the predictions made in the two frames of reference.
^ Does the electron experience a magnetic field from the proton?
^ Compute and , and compare with the strengths of static fields you experience in everyday life: E ∼ 10 6 V/m in a thunderstorm, and B ∼ 10 -3 T for the Earth's magnetic field.
J. Phys.
.^ Does the electron experience a magnetic field from the proton?
^ This field is created by electrons orbiting atoms inside the magnet.
^ The increasing magnetic field causes electrons to circulate (current) around the second coil in such a way as to oppose the increasing magnetic field that the first coil is trying to establish.- Electromagnetic Fields 13 January 2010 10:13 UTC www.tuberose.com [Source type: FILTERED WITH BAYES]
Rev. E 61, 4111 – 4117 (2000).
Top topics
Wikis
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Map
Misc
is a unit vector in the direction of r.^ 
is the electromotive force (or EMF, the voltage generated around a closed loop) and Φm is the magnetic flux—the product of the area times the magnetic field normal to that area.^ 
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