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Electromagnetism
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Ampère’s law · Electric current · Magnetic field · Magnetization · Magnetic flux · Biot–Savart law · Magnetic dipole moment · Gauss's law for magnetism
.Electric current means, depending on the context, a flow of electric charge (a phenomenon) or the rate of flow of electric charge (a quantity).^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Conventional current was defined early in the history of electrical science as a flow of positive charge, although we now know that, in the case of metallic conduction, current is caused by a flow of negatively charged electrons in the opposite direction.
  • Return of the monster! Zilla controller production headed for Washington — Autoblog Green 19 November 2009 18:12 UTC green.autoblog.com [Source type: General]

^ Ampere is the correct term for units of electric current flow, which most people have shortened to amps.
  • Return of the monster! Zilla controller production headed for Washington — Autoblog Green 19 November 2009 18:12 UTC green.autoblog.com [Source type: General]

[1] .This flowing electric charge is typically carried by moving electrons, in a conductor such as wire; in an electrolyte, it is instead carried by ions, and, in a plasma, by both.^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Instead of carrying leaves, electrons carry a tiny amount of electric charge.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ The electrical charge of the atom: electrons and protons (whether or not the numbers are equal).
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

[2]
.The SI unit for measuring the rate of flow of electric charge is the ampere.^ Coulomb: A unit of electric charge.

^ Current: The rate at which electricity flows, measured in amperes, 1 ampere = 1 coulomb per second.

^ Ohm: The unit by which electrical resistance is measured.

.Electric current is measured using an ammeter.^ It's a way of controlling things using incredibly tiny currents of electricity—sometimes even individual electrons!
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Electricity is about using relatively large currents of electrical energy to do useful jobs, like driving a washing machine or powering an electric drill.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Multimeter is a device that can measure the electrical voltage, electrical current, electrical resistance and check continuity.
  • How Electricity is Made 15 September 2009 7:22 UTC www.miniscience.com [Source type: FILTERED WITH BAYES]

[1]

Contents

Physics

Electric current through various media

Metals

.A solid conductive metal contains mobile, or free, electrons.^ Materials such as copper metal that conduct electricity (allow it to flow freely) are called conductors .
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ With careful chemical processing, a semiconductor can be made into n-type semiconductor--a semiconductor that contains a small number of mobile electrons that permit it to carry electric current.
  • BEAM Robotics Tek - solar engine 19 November 2009 18:12 UTC faq.solarbotics.net [Source type: FILTERED WITH BAYES]

^ Metals like copper have "free" electrons that are not bound tightly to their parent atoms.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.These electrons are bound to the metal lattice but not to any individual atom.^ Metals like copper have "free" electrons that are not bound tightly to their parent atoms.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.Even with no external electric field applied, these electrons move about randomly due to thermal energy but, on average, there is zero net current within the metal.^ Conventional current was defined early in the history of electrical science as a flow of positive charge, although we now know that, in the case of metallic conduction, current is caused by a flow of negatively charged electrons in the opposite direction.
  • Return of the monster! Zilla controller production headed for Washington — Autoblog Green 19 November 2009 18:12 UTC green.autoblog.com [Source type: General]

^ Teaching electricity taking students' learning difficulties into account Of course, research in the field of learning electricity has not been restricted to bringing learning difficulties to light but also to address these difficulties in order to improve teaching and learning.

^ Electromagnetic field: Electric and magnetic force field that surrounds a moving electric charge.

.Given a plane through which the wire passes, the number of electrons moving from one side to the other in any period of time is on average equal to the number passing in the opposite direction.^ Calculate the average velocity of electrons through this wire.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ The electrical charge of the atom: electrons and protons (whether or not the numbers are equal).
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ The same technique may be used to "map" wires from one end of a cable to the other, in the event that the wires are not color-coded or otherwise made identifiable.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

.As George Gamow put in his science-popularizing book, One, Two, Three...Infinity (1947), "The metallic substances differ from all other materials by the fact that the outer shells of their atoms are bound rather loosely, and often let one of their electrons go free.^ Metals like copper have "free" electrons that are not bound tightly to their parent atoms.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Diode: A device having two terminals and has a low resistance to electrical current in one direction and a high resistance in the other direction.

^ Unless the atom is electrically charged, it will contain 1 electron as well to balance the charge of the one proton.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

.Thus the interior of a metal is filled up with a large number of unattached electrons that travel aimlessly around like a crowd of displaced persons.^ But a metal surface (the gate) that's separated from the channel by an extremely thin layer of oxide insulator can control the number of electrons on the channel material.
  • BEAM Robotics Tek - solar engine 19 November 2009 18:12 UTC faq.solarbotics.net [Source type: FILTERED WITH BAYES]

.When a metal wire is subjected to electric force applied on its opposite ends, these free electrons rush in the direction of the force, thus forming what we call an electric current."^ A stream of electrons, or an electric current.

^ This is called current electricity or an electric current .
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ The agent may be called electricity or electric current.

A typical wire for electrical conduction is the stranded copper wire.
.When a metal wire is connected across the two terminals of a DC voltage source such as a battery, the source places an electric field across the conductor.^ Voltage: electrical "pressure" between two different points or locations.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ A French physicist called Andre-Marie Ampère (1775–1836) put two electric cables near to one another, wired them up to a power source, and watched them push one another apart.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ There are many, many other sources of DC and AC electricity than what I have mentioned here!
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

.The moment contact is made, the free electrons of the conductor are forced to drift toward the positive terminal under the influence of this field.^ The fundamental difference between an electrical "conductor" and an electrical ïnsulator" is how readily electrons may drift away from their respective atoms.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Momentary switch: A switch with contacts that are made with actuating force and released when that force is removed.

.The free electrons are therefore the current carrier in a typical solid conductor.^ In the timer-controller of claims 1-5, the load circuit (10,10') and the control circuit (12) being operably joined one to the other through the use of solid current conductors.
  • Method and apparatus for timed de-icing - Patent EP0274758 22 September 2009 16:39 UTC www.freepatentsonline.com [Source type: Reference]

^ Certainly, electric current is defined as the "flow" of electrons, but how do electrons "flow" through a solid material such as copper?
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Magnetic filed around a curent carrying wire ....Note the applet shows "conventional" current (that moves opposite to electron flow)-sorry .

.For an electric current of 1 ampere, 1 coulomb of electric charge (which consists of about 6.242 × 1018 elementary charges) drifts every second through any plane through which the conductor passes.^ One ampere is the rate of flow of electric current when one coulomb of charge flows past a point in the circuit in one second.

^ Coulomb: A unit of electric charge.

^ Current: The rate at which electricity flows, measured in amperes, 1 ampere = 1 coulomb per second.

For a steady flow, the current I in amperes can be calculated with the following equation:
I = {Q \over t} \, ,
where Q is the electric charge in coulombs transferred, and t is the time in seconds
More generally, electric current can be represented as the time rate of change of charge, or
I = \frac{dQ}{dt} \, .

Other media

.In metallic solids, electricity flows by means of electrons, from higher to lower electrical potential.^ Activation of the solid state means 60 effectively crowbars the electrical current flow in the load circuit 10 by dint of draining activating electrical signals from the sensing electrodes 32 of the electrical current switching means 30.
  • Method and apparatus for timed de-icing - Patent EP0274758 22 September 2009 16:39 UTC www.freepatentsonline.com [Source type: Reference]

^ An electrical circuit is any continuous path for electrons to flow away from a source of electrical potential (voltage) and back again.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Preferably the solid state current transferring means 30 are not latching type devices, that is the means 30 are not current transfering means that remain in a current transfering or "on" state after the removal of the activating electrical signal from the sensing electrodes 32.
  • Method and apparatus for timed de-icing - Patent EP0274758 22 September 2009 16:39 UTC www.freepatentsonline.com [Source type: Reference]

.In other media, any stream of charged objects may constitute an electric current.^ What does it mean for an object to have an electric charge ?
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ The agent may be called electricity or electric current.

^ A stream of electrons, or an electric current.

So when there is higher cross sectional area there is less resistance. .Conventional currents flows in the opposite way of electron current.^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ The current in a circuit is influenced by a resistor when it comes to this element and transmits this information in the direction of flow and not in the opposite direction.

^ A battery or power outlet creates the electromotive force that makes a current of electrons flow.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.In terms of Ohm's law current is proportional to voltage and inversely proportional to the resistance.^ One ohm is equal to the current of one ampere which will flow when a voltage of one volt is applied .

^ One volt causes a current of one amp through a resistance of one ohm.

^ The difference in potential needed to cause a current of one milliampere flow through a resistance of one ohm.

In a vacuum, a beam of ions or electrons may be formed. .In other conductive materials, the electric current is due to the flow of both positively and negatively charged particles at the same time.^ DOES flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ If a negative charge is flowing to the left, a positive flow to the right is analogous.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ Conductance: The measure of the ability of a material or substance to carry electrical current.

.In still others, the current is entirely due to positive charge flow.^ This in turn causes a greater current to flow from collector (Q2c) to the emitter (Q2e), thus allowing Q1b to see positive.
  • BEAM Robotics Tek - solar engine 19 November 2009 18:12 UTC faq.solarbotics.net [Source type: FILTERED WITH BAYES]

^ One ampere is the rate of flow of electric current when one coulomb of charge flows past a point in the circuit in one second.

^ The following timeline are the events and circuit characteristics while charging and discharging: EVENT - Beginning of charging cycle Capacitor C1 begins to charge due to current from the solar cell and the voltage across C1 rises Q2e is positive, which is required for conduction.
  • BEAM Robotics Tek - solar engine 19 November 2009 18:12 UTC faq.solarbotics.net [Source type: FILTERED WITH BAYES]

.For example, the electric currents in electrolytes are flows of electrically charged atoms (ions), which exist in both positive and negative varieties.^ DOES flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ If a negative charge is flowing to the left, a positive flow to the right is analogous.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.In a common lead-acid electrochemical cell, electric currents are composed of positive hydrogen ions (protons) flowing in one direction, and negative sulfate ions flowing in the other.^ Direct Current: (DC); Electrical current that flows consistently in one direction only.

^ One ohm is equal to the current of one ampere which will flow when a voltage of one volt is applied .

^ Observation of a low or a particularly elevated electrical current flow based on ammeter readings would be an indication to the aircraft operator that the de-icing function was not as desired with respect to one or more de-icing pad.
  • Method and apparatus for timed de-icing - Patent EP0274758 22 September 2009 16:39 UTC www.freepatentsonline.com [Source type: Reference]

.Electric currents in sparks or plasma are flows of electrons as well as positive and negative ions.^ DOES flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ A stream of electrons, or an electric current.

^ PM Electrons do flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

.In ice and in certain solid electrolytes, the electric current is entirely composed of flowing ions.^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Observation of a low or a particularly elevated electrical current flow based on ammeter readings would be an indication to the aircraft operator that the de-icing function was not as desired with respect to one or more de-icing pad.
  • Method and apparatus for timed de-icing - Patent EP0274758 22 September 2009 16:39 UTC www.freepatentsonline.com [Source type: Reference]

^ A circuit is a closed path or loop around which an electric current flows.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.In a semiconductor it is sometimes useful to think of the current as due to the flow of positive "holes" (the mobile positive charge carriers that are places where the semiconductor crystal is missing a valence electron).^ Current: the flow of electrons.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ The mobile electrons at the edge of the n-type semiconductor flow over the boundary (a p-n junction) and fill the mobile holes at the edge of the p-type semiconductor.
  • BEAM Robotics Tek - solar engine 19 November 2009 18:12 UTC faq.solarbotics.net [Source type: FILTERED WITH BAYES]

^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

This is the case in a p-type semiconductor.

Current density

.Current density is a measure of the density of an electric current.^ Cycle: or Hertz; The measurement of the time period of one alternating electric current.

^ What moves through the wire in a circuit is electrical current : a steady flow of electrons, measured in amperes (or amps).
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Current: The rate at which electricity flows, measured in amperes, 1 ampere = 1 coulomb per second.

.It is defined as a vector whose magnitude is the electric current per cross-sectional area.^ Thermocouple: Two dissimilar metals connected at a point, that produce an electrical current whose magnitude is dependent upon the temperature at the junction point.

^ Certainly, electric current is defined as the "flow" of electrons, but how do electrons "flow" through a solid material such as copper?
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Alternating Current: (AC); Electrical current that changes (or alternates) in magnitude and direction of the current at regular intervals.

.In SI units, the current density is measured in amperes per square meter.^ Current-meter measurements from cableways .
  • WSP 2175 19 November 2009 18:12 UTC pubs.usgs.gov [Source type: Academic]

^ Current-meter measurements from ice cover .
  • WSP 2175 19 November 2009 18:12 UTC pubs.usgs.gov [Source type: Academic]

^ Current-meter measurements from boats .
  • WSP 2175 19 November 2009 18:12 UTC pubs.usgs.gov [Source type: Academic]

I = \mathbf{J} \cdot \mathbf{A}
where I is current in the conductor, J is the current density, and A is the cross-sectional area. .The dot product of two vector quantity signifies that electric current is a scalar.^ Diode: A device having two terminals and has a low resistance to electrical current in one direction and a high resistance in the other direction.

^ Consumption comprises the two aspects of devaluation and diminution of the electric current.

^ Thermocouple: Two dissimilar metals connected at a point, that produce an electrical current whose magnitude is dependent upon the temperature at the junction point.

Drift speed

.The mobile charged particles within a conductor move constantly in random directions, like the particles of a gas.^ Now we know that the actual things moving are electrons, with a negative charge, going in the direction opposite of what Franklin thought.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ An adequate model would not draw on individually moving charges (or particles) but on a view where all particles are intimately interconnected.

^ Magnetic Field: A region of space that surrounds a moving electrical charge or a magnetic pole, in which the electrical charge or magnetic pole experiences a force that is above the electrostatic ones associated with particles at rest.

.In order for there to be a net flow of charge, the particles must also move together with an average drift rate.^ One ampere is the rate of flow of electric current when one coulomb of charge flows past a point in the circuit in one second.

^ Electricity: A form of energy produced by the flow of particles of matter and consists of commonly attractive positively (protons [+]) and negatively (electrons [-]) charged atomic particles.

^ Order your custom textbook and lab manual packaged together and save your students 10% off the lab manual’s net (bookstore) price.
  • Pearson - Electronic Devices (Conventional Current Version), 8/E - Thomas L. Floyd 19 November 2009 18:12 UTC www.pearsonhighered.com [Source type: FILTERED WITH BAYES]

.Electrons are the charge carriers in metals and they follow an erratic path, bouncing from atom to atom, but generally drifting in the direction of the electric field.^ Instead of carrying leaves, electrons carry a tiny amount of electric charge.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Saving Electricity 101: Start Here How much it costs / how they charge What's a Watt / Kilowatt?
  • Ask Mr. Electricity: Saving money on refrigerator costs 15 September 2009 7:22 UTC michaelbluejay.com [Source type: General]

^ An atom normally has an equal number of electrons and protons (positively charged particles in its nucleus or centre), so atoms have no overall electrical charge.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

The speed at which they drift can be calculated from the equation:
I=nAvQ \, ,
where
I is the electric current
n is number of charged particles per unit volume (or charge carrier density)
A is the cross-sectional area of the conductor
v is the drift velocity, and
Q is the charge on each particle.
.Electric currents in solids typically flow very slowly.^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ A circuit is a closed path or loop around which an electric current flows.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ One ampere is the rate of flow of electric current when one coulomb of charge flows past a point in the circuit in one second.

.For example, in a copper wire of cross-section 0.5 mm2, carrying a current of 5 A, the drift velocity of the electrons is of the order of a millimetre per second.^ Say, half the first rate: 14.48 ×10 21 electrons per second.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Average electron velocity = 0.000647 feet per second, or 6.47 ×10 −4 ft/s.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Calculate the average velocity of electrons through this wire.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

.To take a different example, in the near-vacuum inside a cathode ray tube, the electrons travel in near-straight lines at about a tenth of the speed of light.^ Take a forward biased diodefor example: electron current flow , the arrow points into the current and moves back "opening" the valve and letscuurent past.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

.Any accelerating electric charge, and therefore any changing electric current, gives rise to an electromagnetic wave that propagates at very high speed outside the surface of the conductor.^ The information of change is transmitted by the electric current.

^ Electromagnetic field: Electric and magnetic force field that surrounds a moving electric charge.

^ Electrochemistry: Chemical changes and energy produced by electric currents.

.This speed is usually a significant fraction of the speed of light, as can be deduced from Maxwell's Equations, and is therefore many times faster than the drift velocity of the electrons.^ Notes: Electricity is fast: the effects of electron motion travel at approximately the speed of light (186,000 miles per second).
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Notes: A significant portion of electrical/electronic circuit problems are caused by nothing more complex than broken wire connections, or faults along the length of wires.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ But for the hobbyist who has plenty of free time but has to order most of the parts they need, it's often easier/faster to verify the part is OK than order everything new.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

.For example, in AC power lines, the waves of electromagnetic energy propagate through the space between the wires, moving from a source to a distant load, even though the electrons in the wires only move back and forth over a tiny distance.^ However even though we know electrons actually flow ..
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ When electrons move, they carry electrical energy from one place to another.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ The voltage is a kind of electrical force that makes electricity move through a wire and we measure it in volts.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.The ratio of the speed of the electromagnetic wave to the speed of light in free space is called the velocity factor, and depends on the electromagnetic properties of the conductor and the insulating materials surrounding it, and on their shape and size.^ Materials such as copper metal that conduct electricity (allow it to flow freely) are called conductors .
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Conductors that let electricity flow freely are said to have a high conductance and a low resistance ; insulators that do not allow electricity to flow are the opposite: they have a low conductance and a high resistance.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Semiconductors are materials that are in between good conductors and good insulators.
  • BEAM Robotics Tek - solar engine 19 November 2009 18:12 UTC faq.solarbotics.net [Source type: FILTERED WITH BAYES]

The nature of these three velocities can be illustrated by an analogy with the three similar velocities associated with gases. The low drift velocity of charge carriers is analogous to air motion; in other words, winds. .The high speed of electromagnetic waves is roughly analogous to the speed of sound in a gas; while the random motion of charges is analogous to heat - the thermal velocity of randomly vibrating gas particles.^ When the valve is opened, fluid motion throughout the system is immediate (actually, the motion progresses at the speed of sound through the fluid - very fast!
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

Electromagnetism

According to Ampère's law, an electric current produces a magnetic field.
.Electric current produces a magnetic field.^ The presence of an electric current will produce a magnetic field, but the mere presence of a voltage will not.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Electrodynamic: The interaction of magnetism and electrical current.

^ Just as electricity may be harnessed to produce magnetism, magnetism may also be harnessed to produce electricity.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

.The magnetic field can be visualized as a pattern of circular field lines surrounding the wire.^ Electromagnetic field: Electric and magnetic force field that surrounds a moving electric charge.

^ When an alternating current passes through a coil of wire, the magnetic field about the coil first expands and then collapses, then expands with its direction reversed, and again collapses.
  • Electricity - ninemsn Encarta 15 September 2009 7:22 UTC au.encarta.msn.com [Source type: FILTERED WITH BAYES]

^ This creates a magnetic field, which causes the electrons in the copper wire to move from atom to atom, creating electricity.
  • Electricity Generation and Distribution 15 September 2009 7:22 UTC www.culverco.com [Source type: Reference]

.Electric current can be directly measured with a galvanometer, but this method involves breaking the circuit, which is sometimes inconvenient.^ In an electrical circuit   Be able to define and measure currents in any element.

^ Break: The act of the opening of an electrical circuit.

^ The formal definition of current (designated by the symbol i) is the number of electric charges (C) that pass a given point in a circuit (a path of current that includes a power source) per second (t).
  • Electricity - Static and current electricity, Electric charge, Electric fields, Coulombs law, Electrical properties 15 September 2009 7:22 UTC www.scienceclarified.com [Source type: FILTERED WITH BAYES]

.Current can also be measured without breaking the circuit by detecting the magnetic field associated with the current.^ What moves through the wire in a circuit is electrical current : a steady flow of electrons, measured in amperes (or amps).
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ The presence of an electric current will produce a magnetic field, but the mere presence of a voltage will not.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ Conversely, an open circuit is one where there is a break preventing any current from going through at all.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

Devices used for this include Hall effect sensors, current clamps, current transformers, and Rogowski coils.
.The theory of Special Relativity allows one to transform the magnetic field into a static electric field for an observer moving at the same speed as the charge in the diagram.^ Electromagnetic field: Electric and magnetic force field that surrounds a moving electric charge.

^ Each strand of hair gets the same static charge and like charges repel, so her hairs push away from one another.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ When electricity flows into the iron core, it creates magnetism.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.The amount of current is particular to a reference frame (who is measuring the current or charge velocity).^ Charge: The measured amount of electrical energy that represents the electrostatic forces between atomic particles.

Ohm's law

Ohm's law states that the current flowing in the metal is directly proportional to the potential difference between two ends(across) of that metal (ideal) resistor (or other ohmic device).i.,e,
V = IR \, ,
where .I is the current, measured in amperes; V is the potential difference, measured in volts; and R is the resistance, measured in ohms.^ What moves through the wire in a circuit is electrical current : a steady flow of electrons, measured in amperes (or amps).
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Ohm Zone (circuit simulator) ....Build series and parallel circuits and measure current and voltage .

Conventions

Current

A diagram showing negative charges (electrons) flowing in the opposite direction of the convertional electric current.
The symbol for a battery in a circuit diagram.
.A flow of positive charge gives the same electric current as a flow of negative charges in the opposite direction.^ DOES flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ If a negative charge is flowing to the left, a positive flow to the right is analogous.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ Impedance: The opposition to electrical flow.

.conventional current is positive in the direction of positive moving charges, and negative in the direction of negative moving charges.^ Current does flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ If polarity is reversed and the diodes position hasn't changed the arrow moves foward with the current and "closes" the valve.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ This imbalance of electrons leaves the former material with a positive charge and the latter with a negative charge.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

.In solid metals such as wires, the positive charge carriers are immobile, and only the negatively charged electrons flow.^ He thought the charge carriers were positively charged.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ DOES flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ If a negative charge is flowing to the left, a positive flow to the right is analogous.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

.Because the electron carries negative charge, the electron motion in a metal is in the direction opposite to that of conventional (or electric) current.^ Electrons, which reside outside the nucleus, have negative electrical charges.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Instead of carrying leaves, electrons carry a tiny amount of electric charge.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

Reference direction

.When solving electrical circuits, the actual direction of current through a specific circuit element is usually unknown.^ Make sure they all understand the nature of electrical current and the importance of continuity throughout the entire circuit.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ A circuit is a closed path or loop around which an electric current flows.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ The electric power in a circuit is equal to the voltage × the current (in other words: watts = volts × amps).
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.Consequently, each circuit element is assigned a current variable with an arbitrarily chosen reference direction.^ Series Circuit: A circuit which may have one or many resistors and/or other various devices connected in a series so that the current has only one path to follow.

^ Electric circuit: An arrangement of any of various conductors through which electric current can flow from a supply current.

.When the circuit is solved, the circuit element currents may have positive or negative values.^ Current does flow from negative to positive.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ Series Circuit: A circuit which may have one or many resistors and/or other various devices connected in a series so that the current has only one path to follow.

^ This allows the current to the load during both the positive and negative alternating of the supply voltage.

.A negative value means that the actual direction of current through that circuit element is opposite that of the chosen reference direction.^ What moves through the wire in a circuit is electrical current : a steady flow of electrons, measured in amperes (or amps).
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ Now we know that the actual things moving are electrons, with a negative charge, going in the direction opposite of what Franklin thought.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ Electric circuit: An arrangement of any of various conductors through which electric current can flow from a supply current.

.In electronic circuits it is usually assumed that all currents flow to ground.^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ A circuit is a closed path or loop around which an electric current flows.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ "Electron Flow" However, for some reason, us engineers always use what's called "conventional current flow", where we say it flows from + to - ...basically, this is done simply by tradition.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

.This usually matches conventional current direction, because power rail is positive in most cases.^ F technically means a milli Farad, or 1/1000 of a Farad, but in reality it usually means a micro Farad because it used to be fairly conventional to abbreviate micro with an 'm', and it still happens in some cases.
  • General electronics question... [Archive] - [H]ard|Forum 19 November 2009 18:12 UTC www.hardforum.com [Source type: Original source]

^ You should notice a direct correlation between the position of the magnet relative to the coil over time, and the amount of voltage or current indicated by the meter.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

Occurrences

.Natural examples include lightning and the solar wind, the source of the polar auroras (the aurora borealis and aurora australis).^ Examples of renewable energy include wind turbines and solar power.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ The remaining regional generation is supplied by natural gas and renewable energy sources—mostly hydropower, wind, and, in New Zealand, geothermal.
  • EIA - International Energy Outlook 2009-Electricity 15 September 2009 7:22 UTC www.eia.doe.gov [Source type: FILTERED WITH BAYES]

.The artificial form of electric current is the flow of conduction electrons in metal wires, such as the overhead power lines that deliver electrical energy across long distances and the smaller wires within electrical and electronic equipment.^ Current: the flow of electrons.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ A stream of electrons, or an electric current.

.In electronics, other forms of electric current include the flow of electrons through resistors or through the vacuum in a vacuum tube, the flow of ions inside a battery or a neuron, and the flow of holes within a semiconductor.^ Current: the flow of electrons.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ A current of electricity is a steady flow of electrons.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

^ A stream of electrons, or an electric current.

Electrical safety

The most obvious hazard is electrical shock. .The amount of current passing through the body, as well as the nature of the contact, the condition of the body part, the current path through the body and the voltage of the source determines the effect.^ The Committee was informed that current meters moored in Flemish Pass by Canada (Bedford Institute of Oceanography) during June 2002 will remain through 2003.
  • SC June 2003 - STACFEN 19 November 2009 18:12 UTC www.nafo.int [Source type: Academic]

^ Voltage and Current Sources .
  • Principles of Electric Circuits: Conventional Current Version: International Edition, 8/E - Pearson Education EMA Catalogue 19 November 2009 18:12 UTC vig.pearsoned.co.uk [Source type: Academic]

.While a very small amount can cause a slight tingle, large amounts can cause severe burns if it passes through the skin or even cardiac arrest if enough passes through the heart.^ Notes: A little math review here: using scientific notation to denote very large (or very small) numbers.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ A short circuit is a circuit having very little resistance, permitting large amounts of current.
  • Basic electricity worksheet : Worksheet 15 September 2009 7:22 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]

^ As one of the few OECD countries with untapped hydroelectric potential, Canada currently has several large- and small-scale hydroelectric facilities currently either planned or under construction.
  • EIA - International Energy Outlook 2009-Electricity 15 September 2009 7:22 UTC www.eia.doe.gov [Source type: FILTERED WITH BAYES]

The effect also varies considerably from individual to individual.[citation needed]
Accidental electric heating can also be dangerous. An overloaded power cable is a frequent cause of fire. .A battery as small as an AA cell placed in a pocket with metal coins can lead to a short circuit heating the battery and the coins which may inflict burns.^ Thus, in a flashlight, there is a simple circuit with a switch, a lamp, and a battery linked together by a few short pieces of copper wire.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

.NiCad, NiMh cells, and lithium batteries are particularly risky because they can deliver a very high current due to their low internal resistance.^ The North Atlantic marine climate is largely controlled by the so-called North Atlantic Oscillation (NAO), which is driven by the pressure difference between the Azores High and the Iceland Low pressure cells.
  • SC Report - June 2006 - STACFEN 19 November 2009 18:12 UTC www.nafo.int [Source type: Academic]

^ Diode: A device having two terminals and has a low resistance to electrical current in one direction and a high resistance in the other direction.

^ Conductors that let electricity flow freely are said to have a high conductance and a low resistance ; insulators that do not allow electricity to flow are the opposite: they have a low conductance and a high resistance.
  • Electricity: Introduction for children, kids, students, young readers!: Explain that Stuff! 15 September 2009 7:22 UTC www.explainthatstuff.com [Source type: FILTERED WITH BAYES]

See also

References

  1. ^ a b Lakatos, John; Oenoki, Keiji; Judez, Hector; Oenoki, Kazushi; Hyun Kyu Cho (March 1998). "Learn Physics Today!". Lima, Peru: Colegio Franklin D. Roosevelt. http://library.thinkquest.org/10796/ch13/ch13.htm. Retrieved 2009-03-10. 
  2. ^ Anthony C. Fischer-Cripps (2004). The electronics companion. CRC Press. p. 13. ISBN 9780750310123. http://books.google.com/books?id=3SsYctmvZkoC&pg=PA13&dq=positive-ions+carrier+current+charge+electrons&lr=&as_brr=3&as_pt=ALLTYPES&ei=RbfWSZnELJeSkASZvbi-Bg. 

External links


Simple English

Current is the flow of electric charge. The equation of current is:

I = \frac{\Delta Q}{\Delta t}
where
I is the current flowing
\Delta Q is the change in electric charge
\Delta t is the change in time

The SI unit of electric current is ampere (A). This is equal to one coulomb of charge in one second. Current can be found in wires, batteries, and lightning.

The source of current

In conducting materials, some electrons are very loosely bound to the atoms of the material. When large amounts of these atoms come together, there is a sort of electron cloud that "hovers" near the atoms of the material. If you examine a cross-section of the piece of conducting material, the electrons will move very quickly through it. This motion is caused by temperature, and electrons flowing in one direction tend to equal the electrons flowing from the other direction, so this is not what causes current to flow.

When an electric field is put on the wire, the electrons respond almost instantly by drifting slightly in the opposite direction of the field. They gain energy from the field, which is lost very quickly when they bump into other electrons in the material. As long as the field is in place, however, the electrons will gain back that energy that they lost, and the process will continue. This "jolt" that electrons receive from the electric field is the source of current, not the overall flow of electrons themselves. From this discussion, we can see two things that current is not:

  • It is not an actual "flow" of electrons in the everyday sense of the word: If we examine the speed given to the electrons by the field, it is usually very small, on the order of millimeters per second. It would take half an hour for electrons to cross a 10-foot room at this rate. Since a light bulb flips on almost immediately after hitting the switch, something else must be at work.
  • It is also not a "domino effect", though this analogy is closer than the flow. Since electrons are so tiny, even when they are moving very quickly they do not have a lot of force behind them. This eliminates the possibility of an electron "bucket brigade" being the source of electric current.

Current in circuits

When current is flowing in a wire circuit, it accelerates when there is no resistance in the circuit. Resistors are used to increase resistance in the circuit so it slows down the current. The relationship between resistance, current, and voltage (another part of the circuit) is shown by Ohm's law.

Ext links

Wikipedia: Electric current


Citable sentences

Up to date as of December 22, 2010

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