# Encyclopedia

V, I, and R, the parameters of Ohm's law.
.In electrical circuits, Ohm's law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them, provided that the temperature remains constant.^ The 'conductor' mentioned by Ohm's law is a circuit element across which the voltage is measured.
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

^ With little voltage across it, its resistance is high.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Figure 1 - ohms law power consumption through a resistance .

[1]
The mathematical equation that describes this relationship is:[2]
$I = \frac{V}{R}$
where .V is the potential difference measured across the resistance in units of volts; I is the current through the resistance in units of amperes and R is the resistance of the conductor in units of ohms.^ Here are the standard units of measurement for electrical current, voltage, and resistance: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ The unit of resistance is the Ohm, named after Georg Ohm .
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

^ I is the current in amperes , V is the potential difference in volts ,and R is a circuit parameter called the resistance (measured in ohms , also equivalent to volts per ampere).
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.More specifically, Ohm's law states that the R in this relation is constant, independent of the current.^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ A similar assumption is made in the statement of Ohm's law: other things being alike, the strength of the current at each point is proportional to the gradient of electric potential.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Written as a mathematical expression, Ohms Law is Resistance(R)=voltage(V)/current(I) or R=V/I The above equation allows you to determine the value of the resistance when the voltage and the current are known.

[3]
.The law was named after the German physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current through simple electrical circuits containing various lengths of wire.^ Ohms Law The relationship between current(I), voltage(V or E), and resistance(R) was discovered by a German scientist named Georg Ohm.

^ In electric circuits, power is a function of both voltage and current.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ The "conductor" mentioned by Ohm's law is a circuit element across which the voltage is measured.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.He presented a slightly more complex equation than the one above (see History section below) to explain his experimental results.^ He presented a slightly more complex equation than the one above to explain his experimental results.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

^ It's \$30 more than the low voltage one.
• Electricity FUBAR question [Archive] - Quarter To Three Forums 11 January 2010 3:30 UTC www.quartertothree.com [Source type: Original source]

^ So, overall, there are more electrons that make it over the various bridges in a certain amount of time than get over just the one "bridge" of the 10-ohm resistor.
• Total Resistence in Parallel circuit - All About Circuits Forum 11 January 2010 3:30 UTC forum.allaboutcircuits.com [Source type: General]

.The above equation is the modern form of Ohm's law.^ This equation is not a modification to Ohm's law.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ The above equation is the modern form of Ohm's law.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Equations for time-invariant AC circuits take the same form as Ohm's law, however, if the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.In physics, the term Ohm's law is also used to refer to various generalizations of the law originally formulated by Ohm.^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Physics Physicists often use the continuum form of Ohm's Law:[3] where J is the current density (current per unit area, unlike the simpler I, units of amperes, of Ohm's law), σ is the conductivity (which can be a tensor in anisotropic materials) and E is the electric field (units of volts per meter, unlike the simpler V, units of volts, of Ohms's law).
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

^ Ohm's law was probably the most important of the early quantitative descriptions of the physics of electricity.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

The simplest example of this is:
$\boldsymbol{J} = \sigma \boldsymbol{E},$
where .J is the current density at a given location in a resistive material, E is the electric field at that location, and σ is a material dependent parameter called the conductivity.^ The electrical resistance of a uniform conductor is given, in terms of conductivity, by: .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Physics Physicists often use the continuum form of Ohm's Law:[3] where J is the current density (current per unit area, unlike the simpler I, units of amperes, of Ohm's law), σ is the conductivity (which can be a tensor in anisotropic materials) and E is the electric field (units of volts per meter, unlike the simpler V, units of volts, of Ohms's law).
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

^ J is the current density (current per unit area, unlike the simpler I, units of amperes, of Ohm's law), σ is the conductivity (which can be a tensor in anisotropic materials) and E is the electric field (units of volts per meter, unlike the simpler V, units of volts, of Ohm's law).
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

This reformulation of Ohm's law is due to Gustav Kirchhoff.[4]

## Microscopic origins of Ohm's law

Drude Model electrons (shown here in blue) constantly bounce between heavier, stationary crystal ions (shown in red).
.The dependence of the current density on the applied electric field is essentially quantum mechanical in nature; (see Classical and quantum conductivity.^ Current density j and field strength E may depend on the coordinates, because U and I depend on the coordinates, e.g.
• Ohms Law and Materials Properties 18 September 2009 7:07 UTC www.tf.uni-kiel.de [Source type: FILTERED WITH BAYES]

^ When an electric field is applied, a slight imbalance develops and a current flows.
• Total Resistence in Parallel circuit - All About Circuits Forum 11 January 2010 3:30 UTC forum.allaboutcircuits.com [Source type: General]

^ Investigate the possible advanced materials and novel nanostructures with enhanced mechanical-to-electrical power coupling efficiency to obtain power densities with magnitudes several orders of higher than the current technologies.
• DARPA FY09.2 SBIR Solicitation Topics 11 January 2010 3:30 UTC www.dodsbir.net [Source type: Academic]

) A qualitative description leading to Ohm's law can be based upon classical mechanics using the Drude model developed by Paul Drude in 1900.[5] [6]
.The Drude model treats electrons (or other charge carriers) like pinballs bouncing between the ions that make up the structure of the material.^ When the temperature of the conductor increases, the collisions between electrons and ions increase.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ So with the red wire ALREADY FILLED with electrons Okay, tell me the diffence (physically or electrically) between the state of atoms on the red wire and the other branch of the wire; before and after power is on.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

^ He is not implying that electrons find that they cannot go one way, so they back up and go the other.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

.Electrons will be accelerated in the opposite direction to the electric field by the average electric field at their location.^ Electrons in this band can be accelerated by the field because there are plenty of nearby states on the band.
• Total Resistence in Parallel circuit - All About Circuits Forum 11 January 2010 3:30 UTC forum.allaboutcircuits.com [Source type: General]

^ Its value is the difference of two large numbers - the average velocity of the individual flies in the drift direction minus the average velocity of the individual flies in the direction opposite to the drift direction.
• Ohms Law and Materials Properties 18 September 2009 7:07 UTC www.tf.uni-kiel.de [Source type: FILTERED WITH BAYES]

^ For a uniform applied field and defining the voltage in the usual convention of opposite direction to the field; .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.With each collision, though, the electron is deflected in a random direction with a velocity that is much larger than the velocity gained by the electric field.^ Electronic circuits can display highly complex behaviors, even though they are governed by the same laws as simple electrical circuits.
• Calculating Voltage/Temperature thresholds - BlazingPC.com 11 January 2010 3:30 UTC www.blazingpc.com [Source type: General]

^ This drift velocity is usually much smaller than the average magnitude of the velocity < v > of the individual flies.
• Ohms Law and Materials Properties 18 September 2009 7:07 UTC www.tf.uni-kiel.de [Source type: FILTERED WITH BAYES]

^ Though the connecting wires take a convoluted path in forming a complete circuit, there are several electrically common points in the electrons' path.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.The net result is that electrons take a tortuous path due to the collisions, but generally drift in a direction opposing the electric field.^ I have always consistently opposed high-tension and alternating systems of electric lighting...not only on account of danger, but because of their general unreliability and unsuitability for any general system of distribution."
• Erroneous Predictions 18 September 2009 7:07 UTC www.foresight.org [Source type: Original source]

^ Though the connecting wires take a convoluted path in forming a complete circuit, there are several electrically common points in the electrons' path.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ An electric circuit is formed when a conductive path is created to allow free electrons to continuously move.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.The drift velocity then determines the electric current density and its relationship to E and is independent of the collisions.^ "Ohm's law states that for many materials (including most metals), the ratio of the current density and electric field is a constant, which is independent of the electric field producing the current.
• Ohms Law - Page 2 - Electronic Circuits Projects Diagrams Free 18 September 2009 7:07 UTC www.electro-tech-online.com [Source type: Original source]

^ J is the current density (current per unit area, unlike the simpler I, units of amperes, of Ohm's law), σ is the conductivity (which can be a tensor in anisotropic materials) and E is the electric field (units of volts per meter, unlike the simpler V, units of volts, of Ohm's law).
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ There are, however, components of electrical circuits which do not obey Ohm's law; that is, their relationship between current and voltage (their I–V curve ) is nonlinear.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Drude calculated the average drift velocity from p = −eEτ where p is the average momentum, −e is the charge of the electron and τ is the average time between the collisions.^ When the temperature of the conductor increases, the collisions between electrons and ions increase.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Since both the momentum and the current density are proportional to the drift velocity, the current density becomes proportional to the applied electric field; this leads to Ohm's law.^ But on the whole, ohm's law does not apply.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ When an electric field is applied, a slight imbalance develops and a current flows.
• Total Resistence in Parallel circuit - All About Circuits Forum 11 January 2010 3:30 UTC forum.allaboutcircuits.com [Source type: General]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

## Temperature effects

.Ohm's law has sometimes been stated as, "for a conductor in a given state, the electromotive force is proportional to the current produced."^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

^ Actually, Ohm wrote (translated): "In a point of a homogeneous conductor through which permanent currents flow, the electromotive force is identical in both amplitude and direction to the electrostatic force as given by Coulomb's law".
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

That is, that the resistance, the ratio of the applied electromotive force (or voltage) to the current, "does not vary with the current strength ." The qualifier "in a given state" is usually interpreted as meaning "at a constant temperature," since the resistivity of materials is usually temperature dependent. .Because the conduction of current is related to Joule heating of the conducting body, according to Joule's first law, the temperature of a conducting body may change when it carries a current.^ However, these power equations are so commonly associated with the Ohm's Law equations relating voltage, current, and resistance (E=IR ; I=E/R ; and R=E/I) that they are frequently credited to Ohm.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ It will be one value when you just turn the lightbulb on (and the filament is cold) and a different value when the filament is hot because the filament does not obey ohm's law, resistance is variable with temperature.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ Hungryhaney First of all, the resistance of your mouth can vary dramatically because the mouth contains fluids, and contaminated fluids can conduct electricity with little resistance.
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

.The dependence of resistance on temperature therefore makes resistance depend upon the current in a typical experimental setup, making the law in this form difficult to directly verify.^ What its (specific) resistance will be, including its temperature dependence.
• Ohms Law and Materials Properties 18 September 2009 7:07 UTC www.tf.uni-kiel.de [Source type: FILTERED WITH BAYES]

^ Just as the resistance of a conductor depends upon temperature, the resistance of a conductor depends upon strain .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ In the 1920s, it was discovered that the current through an ideal resistor actually has statistical fluctuations, which depend on temperature, even when voltage and resistance are exactly constant; this fluctuation, now known as Johnson–Nyquist noise , is due to the discrete nature of charge.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Maxwell and others worked out several methods to test the law experimentally in 1876, controlling for heating effects.^ Your other questions need to be answered by: Lenz's "Law" No I can't forget Mr. Maxwell !
• Ohms Law - Page 2 - Electronic Circuits Projects Diagrams Free 18 September 2009 7:07 UTC www.electro-tech-online.com [Source type: Original source]

^ Ohm's work long preceded Maxwell's equations and any understanding of frequency-dependent effects in AC circuits.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ The accuracy of the assumption that flow is proportional to the gradient is more readily tested, using modern measurement methods, for the electrical case than for the heat case.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

[7]

## Hydraulic analogy

.A hydraulic analogy is sometimes used to describe Ohm's Law.^ A hydraulic analogy is sometimes used to describe Ohm's Law.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ I usually use ohm's law for calculating resistors in LED circuits in small-time prop projects.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

.Water pressure, measured by pascals (or PSI), is the analog of voltage because establishing a water pressure difference between two points along a (horizontal) pipe causes water to flow.^ Water pressure, measured by pascals (or PSI ), is the analog of voltage because establishing a water pressure difference between two points along a (horizontal) pipe causes water to flow.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Voltage is a specific measure of potential energy that is always relative between two points.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Voltage is like the size of the pipe, amps are like the pressure of water through the pipe.
• Electricity FUBAR question [Archive] - Quarter To Three Forums 11 January 2010 3:30 UTC www.quartertothree.com [Source type: Original source]

.Water flow rate, as in liters per second, is the analog of current, as in coulombs per second.^ Water flow rate, as in liters per second, is the analog of current, as in coulombs per second.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ An Amp is a Coulomb per second.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

^ We say that the rate of water flow through an aperture restrictor is proportional to the difference in water pressure across the restrictor.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Finally, flow restrictors — such as apertures placed in pipes between points where the water pressure is measured — are the analog of resistors.^ Finally, flow restrictors — such as apertures placed in pipes between points where the water pressure is measured — are the analog of resistors.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Water pressure, measured by pascals (or PSI ), is the analog of voltage because establishing a water pressure difference between two points along a (horizontal) pipe causes water to flow.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Water begins flowing out of the faucet immediately, but water further away does not start moving until it "feels" the drop in pressure ahead of it, as water molecules start to move.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

.We say that the rate of water flow through an aperture restrictor is proportional to the difference in water pressure across the restrictor.^ We say that the rate of water flow through an aperture restrictor is proportional to the difference in water pressure across the restrictor.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

^ The current in a circuit is directly proportional to the electric potential difference impressed across its ends and inversely proportional to the total resistance offered by the external circuit.

.Similarly, the rate of flow of electrical charge, that is, the electric current, through an electrical resistor is proportional to the difference in voltage measured across the resistor.^ We say that the rate of water flow through an aperture restrictor is proportional to the difference in water pressure across the restrictor.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ As the current encounters the 5 Ω resistance, voltage is dropped across the resistor's ends.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Electric current is the flow of electric charge by moving electrons.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

.Flow and pressure variables can be calculated in fluid flow network with the use of the hydraulic ohm analogy.^ A hydraulic analogy is sometimes used to describe Ohm's Law.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Flow and pressure variables can be calculated in fluid flow network with the use of the hydraulic ohm analogy.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ It may not always be useful, especially if you are dealing with active components, and if you have a few inductors or capacitors then you have to convert to the frequency domain to use (a variation of)ohm's law on them.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

[8][9] .The method can be applied to both steady and transient flow situations.^ The method can be applied to both steady and transient flow situations.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.In the linear laminar flow region, Poiseuille's law describes the hydraulic resistance of a pipe, but in the turbulent flow region the pressure–flow relations become nonlinear.^ Poiseuille's law Scientific laws named after people Ohm's acoustic law Hydraulic analogy Hopkinson's Law ("Ohm's Law for magnetics") Sheet resistance Walking along the resistive film - building various resistive circuits by reproducing Ohm's experiment nowadays .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Ohm's Law states that I=V/R. The toddlers skin would have to have an EXTREMELY low resistance for enough current to flow at 12v.
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

^ If the resistance to water flow stays the same and the pump pressure increases, the flow rate must also increase.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

## Circuit analysis

In circuit analysis, three equivalent expressions of Ohm's law are used interchangeably:
$V = IR \quad ext{or} \quad I = \frac{V}{R} \quad ext{or} \quad R = \frac{V}{I}$
.Indeed, each is quoted by some sources as the defining relationship of Ohm's law,[2][10][11] or all three are quoted,[12] or derived from a proportional form,[13] or even just the two that do not correspond to Ohm's original statement may sometimes be given.^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ "We stress that the relationship V=IR is not a statement of Ohm's law.
• Ohms Law - Page 2 - Electronic Circuits Projects Diagrams Free 18 September 2009 7:07 UTC www.electro-tech-online.com [Source type: Original source]

^ All Ohm's law says is that Voltage is directly proportional to amps.
• crap economy? watch your speed guys [Archive] - Steam Users' Forums 11 January 2010 3:30 UTC forums.steampowered.com [Source type: Original source]

[14][15]

### Resistive circuits

.Resistors are circuit elements that impede the passage of electric charge in agreement with Ohm's law, and are designed to have a specific resistance value R.^ Resistors are conductors that slow down the passage of electric charge.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ This symbol represents a resistor, and the R designates its resistance.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

.In a schematic diagram the resistor is shown as a zig-zag symbol.^ The most common schematic symbol for a resistor is a zig-zag line: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Real resistors look nothing like the zig-zag symbol.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Sometimes resistor symbols are used in schematic diagrams to designate a non-specific load, rather than an actual resistor.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.An element (resistor or conductor) that behaves according to Ohm's law over some operating range is referred to as an ohmic device (or an ohmic resistor) because Ohm's law and a single value for the resistance suffice to describe the behavior of the device over that range.^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ The resistance of most resistive devices ( resistors ) is constant over a large range of values of current and voltage.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ When a resistor is used under these conditions, the resistor is referred to as an ohmic device (or an ohmic resistor ) because a single value for the resistance suffices to describe the resistive behavior of the device over the range.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Ohm's law holds for circuits containing only resistive elements (no capacitances or inductances) for all forms of driving voltage or current, regardless of whether the driving voltage or current is constant (DC) or time-varying such as AC.^ Equations for time-invariant AC circuits take the same form as Ohm's law, however, if the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ However, the resistance will not be constant and it will NOT equal voltage/current.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.At any instant of time Ohm's law is valid for such circuits.^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

^ Equations for time-invariant AC circuits take the same form as Ohm's law, however, if the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Resistor values in ohms are usually shown as an adjacent number, and if several resistors are present in a circuit, they will be labeled with a unique identifier number such as R 1 , R 2 , R 3 , etc.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Resistors which are in series or in parallel may be grouped together into a single "equivalent resistance" in order to apply Ohm's law in analyzing the circuit.^ Well, not really, it's a circuit with parallel resistors.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ But on the whole, ohm's law does not apply.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

.This application of Ohm's law is illustrated with examples in "How To Analyze Resistive Circuits Using Ohm's Law" on wikiHow.^ Ohm's Law is a very simple and useful tool for analyzing electric circuits.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ How electrical engineers use Ohm's law .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

### Reactive circuits with time-varying signals

.When reactive elements such as capacitors, inductors, or transmission lines are involved in a circuit to which AC or time-varying voltage or current is applied, the relationship between voltage and current becomes the solution to a differential equation, so Ohm's law (as defined above) does not directly apply since that form contains only resistances having value R, not complex impedances which may contain capacitance ("C") or inductance ("L").^ Equations for time-invariant AC circuits take the same form as Ohm's law, however, if the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ The complex generalization of resistance is impedance , usually denoted Z ; it can be shown that for an inductor, .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Equations for time-invariant AC circuits take the same form as Ohm's law, however, the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials.^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's law for power: Power equals Voltage times Current.
• Backlinks to www.sengpielaudio.com back links - Mikrofonaufnahme und Tonstudiotechnik Some Back Links - Senkpiel ist immer Sengpiel - sengpielaudio Eberhard Sengpiel Berlin 11 January 2010 3:30 UTC www.sengpielaudio.com [Source type: FILTERED WITH BAYES]

^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

[16]
.In this approach, a voltage or current waveform takes the form Aest, where t is time, s is a complex parameter, and A is a complex scalar.^ Now that we know the current, we can take that value and multiply it by the voltage to determine power: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ If you hook up a lightbulb to a battery, both the voltage and the current will be constant (for some small amount of time as the battery does drain).
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ Ohm expressed his discovery in the form of a simple equation, describing how voltage, current, and resistance interrelate: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.In any linear time-invariant system, all of the currents and voltages can be expressed with the same s parameter as the input to the system, allowing the time-varying complex exponential term to be canceled out and the system described algebraically in terms of the complex scalars in the current and voltage waveforms.^ Equations for time-invariant AC circuits take the same form as Ohm's law, however, if the variables are generalized to complex numbers and the current and voltage waveforms are complex exponentials .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ In this approach, a voltage or current waveform takes the form A e s t , where t is time, s is a complex parameter, and A is a complex scalar.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ In any linear time-invariant system , all of the currents and voltages can be expressed with the same s parameter as the input to the system, allowing the time-varying complex exponential term to be canceled out and the system described algebraically in terms of the complex scalars in the current and voltage waveforms.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

The complex generalization of resistance is impedance, usually denoted Z; it can be shown that for an inductor,
$Z = sL\,$
and for a capacitor,
$Z = \frac{1}{sC}.$
We can now write,
$\boldsymbol{V} = \boldsymbol{I} \cdot \boldsymbol{Z}$
where .V and I are the complex scalars in the voltage and current respectively and Z is the complex impedance.^ V and I are the complex scalars in the voltage and current respectively and Z is the complex impedance.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ In any linear time-invariant system , all of the currents and voltages can be expressed with the same s parameter as the input to the system, allowing the time-varying complex exponential term to be canceled out and the system described algebraically in terms of the complex scalars in the current and voltage waveforms.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ The real parts of such complex current and voltage waveforms describe the actual sinusoidal currents and voltages in a circuit, which can be in different phases due to the different complex scalars.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.This form of Ohm's law, with Z taking the place of R, generalizes the simpler form.^ How about, instead, we discuss the form of "torture" which is, you know, the topic of this thread, and when TPM starts a thread about electric-shock to testicles, or even Ohm's Law in general, I will be happy to discuss that in minute detail with you?
• TPMmuckraker | Talking Points Memo | Mukasey Says Waterboarding "Repugnant" But Refuses Outright Condemnation 11 January 2010 3:30 UTC tpmmuckraker.talkingpointsmemo.com [Source type: Original source]
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^ No - they don't follow Ohm's law in a strictly linear fashion - nothing about ohm's law says anything about linearity in the first place.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ There are other mathematical principles of electricity that do take polarity into account through the use of signs (+ or -), but not Ohm's Law.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

When Z is complex, only the real part is responsible for dissipating heat.
.In the general AC circuit, Z varies strongly with the frequency parameter s, and so also will the relationship between voltage and current.^ In the general AC circuit, Z will vary strongly with the frequency parameter s , and so also will the relationship between voltage and current.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ In any linear time-invariant system , all of the currents and voltages can be expressed with the same s parameter as the input to the system, allowing the time-varying complex exponential term to be canceled out and the system described algebraically in terms of the complex scalars in the current and voltage waveforms.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ When such reactive elements, or transmission lines, are involved in a circuit, the relationship between voltage and current becomes the solution to a differential equation.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.For the common case of a steady sinusoid, the s parameter is taken to be jω, corresponding to a complex sinusoid Aejωt.^ For the common sinusoidal case, the s parameter is taken to be j ω , corresponding to a complex sinusoid A e j ω t .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.The real parts of such complex current and voltage waveforms describe the actual sinusoidal currents and voltages in a circuit, which can be in different phases due to the different complex scalars.^ The real parts of such complex current and voltage waveforms describe the actual sinusoidal currents and voltages in a circuit, which can be in different phases due to the different complex scalars.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ V and I are the complex scalars in the voltage and current respectively and Z is the complex impedance.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ In this approach, a voltage or current waveform takes the form A e s t , where t is time, s is a complex parameter, and A is a complex scalar.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

### Linear approximations

.Ohm's law is one of the basic equations used in the analysis of electrical circuits.^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ This equation is not a modification to Ohm's law.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ How electrical engineers use Ohm's law .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.It applies to both metal conductors and circuit components (resistors) specifically made for this behaviour.^ It applies to both metal conductors and circuit components ( resistors ) specifically made for this behaviour.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ There are circuit components specifically engineered to provide nonlinear resistance curves, one of them being the varistor .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ So far, we've been analyzing single-battery, single-resistor circuits with no regard for the connecting wires between the components, so long as a complete circuit is formed.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Both are ubiquitous in electrical engineering.^ Both are ubiquitous in electrical engineering.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Now, Mr. Electrical Engineer, it is time for both of us to "put-up or shut-up."
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

.Materials and components that obey Ohm's law are described as "ohmic" [17] which means they produce the same value for resistance (R = V/I) regardless of the value of V or I which is applied and whether the applied voltage or current is DC (direct current) of either positive or negative polarity or AC (alternating current).^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ But on the whole, ohm's law does not apply.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ With current steady, voltage follows resistance (an increase in resistance means an increase in voltage).
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.In a true ohmic device, the same value of resistance will be calculated from R = V/I regardless of the value of the applied voltage V. That is, the ratio of V/I is constant, and when current is plotted as a function of voltage the curve is linear (a straight line).^ The plot is no longer a straight line.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ A "linear" function in mathematics is one that tracks a straight line when plotted on a graph.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ So although current and voltage stay the same, the resistance changes.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

.If voltage is forced to some value V, then that voltage V divided by measured current I will equal R. Or if the current is forced to some value I, then the measured voltage V divided by that current I is also R. Since the plot of I versus V is a straight line, then it is also true that for any set of two different voltages V1 and V2 applied across a given device of resistance R, producing currents I1 = V1/R and I2 = V2/R, that the ratio (V1-V2)/(I1-I2) is also a constant equal to R. The operator "delta" (Δ} is used to represent a difference in a quantity, so we can write ΔV = V1-V2 and ΔI = I1-I2.^ The resistance of most resistive devices ( resistors ) is constant over a large range of values of current and voltage.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ With little voltage across it, its resistance is high.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Summarizing, for any truly ohmic device having resistance R, V/I = ΔV/ΔI = R for any applied voltage or current or for the difference between any set of applied voltages or currents.^ How voltage, current, and resistance relate .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

^ "In a true ohmic device, the same value of resistance will be calculated from R = V/I regardless of the value of the applied voltage V. That is, the ratio of V/I is constant, and when current is plotted as a function of voltage the curve is linear (a straight line)."
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

.
Plot of I–V curve of an ideal p-n junction diode at 1μA reverse leakage current.
^ Plot of I–V curve of an ideal p-n junction diode at 1μA reverse leakage current.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Ohm%27s_law Since we're agreed that when current is plotted against voltage, the curve is not linear for a light bulb, it's obviously not ohmic.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

Failure of the device to follow Ohm's law is clearly shown since the curve is not a straight line.
.There are, however, components of electrical circuits which do not obey Ohm's law; that is, their relationship between current and voltage (their I–V curve) is nonlinear.^ In electric circuits, power is a function of both voltage and current.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ There are, however, components of electrical circuits which do not obey Ohm's law; that is, their relationship between current and voltage (their I–V curve ) is nonlinear.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Calculation of Ohm's law · The Magic Triangle Calculation of electric power, voltage, current and resistance .
• Backlinks to www.sengpielaudio.com back links - Mikrofonaufnahme und Tonstudiotechnik Some Back Links - Senkpiel ist immer Sengpiel - sengpielaudio Eberhard Sengpiel Berlin 11 January 2010 3:30 UTC www.sengpielaudio.com [Source type: FILTERED WITH BAYES]

.An example is the p-n junction diode (curve at right).^ An example is the p-n junction diode .
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Plot of I–V curve of an ideal p-n junction diode at 1μA reverse leakage current.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.As seen in the figure, the current does not increase linearly with applied voltage for a diode.^ As it progresses to the right we see the line flattening out, the circuit requiring greater and greater increases in voltage to achieve equal increases in current.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ If we were to plot current over voltage on a graph as we did with the lamp circuit, the effect of ionization would be clearly seen as nonlinear: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Swipecat, on 10/03/2009 , -0/+1 A light bulb filament is a metal, which is Ohmic, meaning that the current is (near enough) proportional to the applied voltage at a given temperature.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

.One can determine a value of current (I) for a given value of applied voltage (V) from the curve, but not from Ohm's law, since the value of "resistance" is not constant as a function of applied voltage.^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ If we try to apply Ohm's Law to find the resistance of this lamp circuit with the voltage and current values plotted above, we arrive at several different values.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Further, the current only increases significantly if the applied voltage is positive, not negative.^ As it progresses to the right we see the line flattening out, the circuit requiring greater and greater increases in voltage to achieve equal increases in current.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Because the slope of the current/voltage for this phenomenon is negative (angling down instead of up as it progresses from left to right), it is known as negative resistance .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Swipecat, on 10/03/2009 , -0/+1 A light bulb filament is a metal, which is Ohmic, meaning that the current is (near enough) proportional to the applied voltage at a given temperature.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

.The ratio V/I for some point along the nonlinear curve is sometimes called the static, or chordal, or DC, resistance[18][19], but as seen in the figure the value of total V over total I varies depending on the particular point along the nonlinear curve which is chosen.^ Here is a further statement, " This quantity is sometimes called simply resistance, although the two definitions are equivalent only for an ohmic component such as an ideal resistor."
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ There are circuit components specifically engineered to provide nonlinear resistance curves, one of them being the varistor .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ It will be one value when you just turn the lightbulb on (and the filament is cold) and a different value when the filament is hot because the filament does not obey ohm's law, resistance is variable with temperature.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

.This means the "DC resistance" V/I at some point on the curve is not the same as what would be determined by applying an AC signal having peak amplitude ΔV volts or ΔI amps centered at that same point along the curve and measuring ΔV/ΔI. However, in some diode applications, the AC signal applied to the device is small and it is possible to analyze the circuit in terms of the dynamic, small-signal, or incremental resistance, defined as the one over the slope of the V–I curve at the average value (DC operating point) of the voltage (that is, one over the derivative of current with respect to voltage).^ The resistance of most resistive devices ( resistors ) is constant over a large range of values of current and voltage.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ With current steady, voltage follows resistance (an increase in resistance means an increase in voltage).
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ However, in some diode applications, the AC signal applied to the device is small and it is possible to analyze the circuit in terms of the dynamic , small-signal , or incremental resistance, defined as the slope of the V–I curve (or inverse slope of the I–V curve, that is, the derivative of current with respect to voltage).
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.For sufficiently small signals, the dynamic resistance allows the Ohm's law small signal resistance to be calculated as approximately one over the slope of a line drawn tangentially to the V-I curve at the DC operating point.^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ For sufficiently small signals, the dynamic resistance allows the Ohm's law proportionality to be applied as an approximation.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ A similar assumption is made in the statement of Ohm's law: other things being alike, the strength of the current at each point is proportional to the gradient of electric potential.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

[20]

## Relation to heat conductions

Ohm's principle predicts the flow of electrical charge (i.e. current) in electrical conductors when subjected to the influence of voltage differences; Jean-Baptiste-Joseph Fourier's principle predicts the flow of heat in heat conductors when subjected to the influence of temperature differences.
.The same equation describes both phenomena, the equation's variables taking on different meanings in the two cases.^ Both phenomena can exist simultaneously in the same system.
• TPMmuckraker | Talking Points Memo | Mukasey Says Waterboarding "Repugnant" But Refuses Outright Condemnation 11 January 2010 3:30 UTC tpmmuckraker.talkingpointsmemo.com [Source type: Original source]
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^ Horsepower and watts are merely two different units for describing the same kind of physical measurement, with 1 horsepower equaling 745.7 watts.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's law describes both an instantaneous and average value because it's only applicable to a linear relationship between V and I where the instantaneous and average values are the same.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

Specifically, solving a heat conduction (Fourier) problem with temperature (the driving "force") and flux of heat (the rate of flow of the driven "quantity", i.e. heat energy) variables also solves an analogous electrical conduction (Ohm) problem having electric potential (the driving "force") and electric current (the rate of flow of the driven "quantity", i.e. charge) variables.
The basis of Fourier's work was his clear conception and definition of thermal conductivity. .He assumed that, all else being the same, the flux of heat is strictly proportional to the gradient of temperature.^ He assumed that, all else being the same, the flux of heat is strictly proportional to the gradient of temperature.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ A similar assumption is made in the statement of Ohm's law: other things being alike, the strength of the current at each point is proportional to the gradient of electric potential.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Although undoubtedly true for small temperature gradients, strictly proportional behavior will be lost when real materials (e.g.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Although undoubtedly true for small temperature gradients, strictly proportional behavior will be lost when real materials (e.g.^ Although undoubtedly true for small temperature gradients, strictly proportional behavior will be lost when real materials (e.g.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ He assumed that, all else being the same, the flux of heat is strictly proportional to the gradient of temperature.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

ones having a thermal conductivity that is a function of temperature) are subjected to large temperature gradients.
.A similar assumption is made in the statement of Ohm's law: other things being alike, the strength of the current at each point is proportional to the gradient of electric potential.^ A similar assumption is made in the statement of Ohm's law: other things being alike, the strength of the current at each point is proportional to the gradient of electric potential.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's law was probably the most important of the early quantitative descriptions of the physics of electricity.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.The accuracy of the assumption that flow is proportional to the gradient is more readily tested, using modern measurement methods, for the electrical case than for the heat case.^ In this case, however, power (P) is exactly equal to current (I) multiplied by voltage (E), rather than merely being proportional to IE. When using this formula, the unit of measurement for power is the watt , abbreviated with the letter "W." .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Newer houses suffer the same possibility but usually with less frequency because they use Copper now and modern wire can withstand heat better.
• Electricity FUBAR question [Archive] - Quarter To Three Forums 11 January 2010 3:30 UTC www.quartertothree.com [Source type: Original source]

^ As odd as it may seem, the actual mathematical relationship between pressure, flow, and resistance is actually more complex for fluids like water than it is for electrons.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

## Other versions of Ohm's law

.Ohm's law, in the form above, is an extremely useful equation in the field of electrical/electronic engineering because it describes how voltage, current and resistance are interrelated on a "macroscopic" level, that is, commonly, as circuit elements in an electrical circuit.^ If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Here are the standard units of measurement for electrical current, voltage, and resistance: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Physicists who study the electrical properties of matter at the microscopic level use a closely related and more general vector equation, sometimes also referred to as Ohm's law, having variables that are closely related to the V, I, and R scalar variables of Ohm's law, but are each functions of position within the conductor.^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ The law was proposed by physicist Georg Ohm, who also proposed famous electrical law, which is similarly called Ohm's law."
• Belkin's RockStar channels jams to five others -- Engadget 11 January 2010 3:30 UTC www.engadget.com [Source type: FILTERED WITH BAYES]

^ Ohm's law states that, in an electrical circuit, the current passing through a conductor between two points is directly proportional to the potential difference (i.e.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

Physicists often use this continuum form of Ohm's Law:[21]
$\mathbf{E} = \rho \mathbf{J}$
where ."E" is the electric field vector with units of volts per meter (analogous to "V" of Ohm's law which has units of volts), "J" is the current density vector with units of amperes per unit area (analogous to "I" of Ohm's law which has units of amperes), and "ρ" (Greek "rho") is the resistivity with units of ohm·meters (analogous to "R" of Ohm's law which has units of ohms).^ Calculation of Ohm's law · The Magic Triangle Calculation of electric power, voltage, current and resistance .
• Backlinks to www.sengpielaudio.com back links - Mikrofonaufnahme und Tonstudiotechnik Some Back Links - Senkpiel ist immer Sengpiel - sengpielaudio Eberhard Sengpiel Berlin 11 January 2010 3:30 UTC www.sengpielaudio.com [Source type: FILTERED WITH BAYES]

^ Here are the standard units of measurement for electrical current, voltage, and resistance: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

The above equation is sometimes written[22] as J = σE where "σ" is the conductivity which is the reciprocal of ρ.
Current flowing through a uniform cylindrical conductor (such as a round wire) with a uniform field applied.
The potential difference between two points is defined as:[23]
${\Delta V} = -\int {\mathbf E \cdot d \mathbf l}$
with $d \mathbf l$ the element of path along the integration of electric field vector E. If the applied E field is uniform and oriented along the length of the conductor as shown in the figure, then defining the voltage V in the usual convention of being opposite in direction to the field (see figure), and with the understanding that the voltage V is measured differentially across the length of the conductor allowing us to drop the Δ symbol, the above vector equation reduces to the scalar equation:
$V = {E}{l} \ \ ext{or} \ \ E = \frac{V}{l}$
Since the E field is uniform in the direction of wire length, for a conductor having uniformly consistent resistivity ρ, the current density J will also be uniform in any cross-sectional area and oriented in the direction of wire length, so we may write:[24]
$J = \frac{I}{a}$
Substituting the above 2 results (for E and J respectively) into the continuum form shown at the beginning of this section:
$\frac{V}{l} = \frac{I}{a}\rho \qquad ext{or} \qquad V = I \rho \frac{l}{a}$
The electrical resistance of a uniform conductor is given in terms of resistivity by:[24]
${R} = \rho \frac{l}{a}$
where .l is the length of the conductor in SI units of meters, a is the cross-sectional area (for a round wire a = πr2 if r is radius) in units of meters squared, and ρ is the resistivity in units of ohm·meters.^ That step function in voltage propagates down the twisted pair wire at c/n, where n is related to the capacitance and inductance per unit length of the transmission line.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

^ The conductivity ( ) of a material is determined by taking the reciprocal of the measured electrical resistance (R) to the flow of electricity in a length (L) of material divided by the cross-sectional area (A).
• Calculating Voltage/Temperature thresholds - BlazingPC.com 11 January 2010 3:30 UTC www.blazingpc.com [Source type: General]

^ With wire resistance being zero, the voltage drop across any continuous stretch of wire can be determined through Ohm's Law as such: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

After substitution of R from the above equation into the equation preceding it, the continuum form of Ohm's law for a uniform field (and uniform current density) oriented along the length of the conductor reduces to the more familiar form:
${V}={I}{R} \$
.A perfect crystal lattice, with low enough thermal motion and no deviations from periodic structure, would have no resistivity,[25] but a real metal has crystallographic defects, impurities, multiple isotopes, and thermal motion of the atoms.^ The bus speed can be increased for a stable OC as long as the resistance is low enough for the signal to flow unimpeded along the circuit.
• Calculating Voltage/Temperature thresholds - BlazingPC.com 11 January 2010 3:30 UTC www.blazingpc.com [Source type: General]

^ In such a case, there would be zero resistance, a lot of heat and possibly sparks just prior and just after every moment the metal made contact.
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

^ Likewise, if we were to have a short circuit constructed of a loop of superconducting wire (absolutely zero resistance), we could have a condition of current in the loop with zero voltage, and likewise no power would be dissipated.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Electrons scatter from all of these, resulting in resistance to their flow.^ All of this makes sense, of course, so long as the lamp continues to provide exactly the same amount of friction (resistance) to the flow of electrons through it: 3 Ω.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ As odd as it may seem, the actual mathematical relationship between pressure, flow, and resistance is actually more complex for fluids like water than it is for electrons.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.The more complex generalized forms of Ohm's law are important to condensed matter physics, which studies the properties of matter and, in particular, its electronic structure.^ How about, instead, we discuss the form of "torture" which is, you know, the topic of this thread, and when TPM starts a thread about electric-shock to testicles, or even Ohm's Law in general, I will be happy to discuss that in minute detail with you?
• TPMmuckraker | Talking Points Memo | Mukasey Says Waterboarding "Repugnant" But Refuses Outright Condemnation 11 January 2010 3:30 UTC tpmmuckraker.talkingpointsmemo.com [Source type: Original source]
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^ It will be critically important in the analysis of more complex circuits involving multiple resistors and/or batteries.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ For purposes of this discussion I am focusing on electrical breakdown as it relates to an electrical circuit and in particular current (electron) migration (more on this later).
• Calculating Voltage/Temperature thresholds - BlazingPC.com 11 January 2010 3:30 UTC www.blazingpc.com [Source type: General]

In broad terms, they fall under the topic of constitutive equations and the theory of transport coefficients.

### Magnetic effects

The continuum form of the equation is only valid in the reference frame of the conducting material. If the material is moving at velocity v relative to a magnetic field B, a term must be added as follows:
$\mathbf{E} + \mathbf{v} imes\mathbf{B} = \mathbf{J}{\rho}$
See Lorentz force for more on this and Hall effect for some other implications of a magnetic field. .This equation is not a modification to Ohm's law.^ However, these power equations are so commonly associated with the Ohm's Law equations relating voltage, current, and resistance (E=IR ; I=E/R ; and R=E/I) that they are frequently credited to Ohm.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Surveying our array of Ohm's Law equations, we find two equations that give us answers from known quantities of voltage and current: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ It should be understood that polarity has nothing to do with Ohm's Law: there will never be negative voltages, currents, or resistance entered into any Ohm's Law equations!
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Rather, it is analogous in circuit analysis terms to taking into account inductance as well as resistance.^ There are other mathematical principles of electricity that do take polarity into account through the use of signs (+ or -), but not Ohm's Law.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ If we were to triple the voltage in our last example circuit from 10 to 30 volts and keep the circuit resistance unchanged, we would expect the current to triple as well.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

## Ohm's law in a plasma

In plasma physics, the generalized Ohm's law is given by
$\mathbf{E} + \mathbf{V} imes\mathbf{B} = {\eta}\mathbf{J} + \frac{\mathbf{J} imes\mathbf{B}}{ne} - \frac{ abla \cdot \mathsf{P}_e}{ne} + \frac{m_e}{ne^2} \left[\frac{\partial\mathbf{J}}{\partial t} + abla\cdot\left(\mathbf{JV}+\mathbf{VJ}-\frac{\mathbf{JJ}}{ne}\right)\right],$
where .$\mathbf{V}$ is the bulk (center of mass) velocity of the plasma, η is the plasma resistivity, n is the number density, $\mathsf{P}_e$ is the electron pressure tensor, and the quantities $\mathbf{JV}$, $\mathbf{JV}$, and $\mathbf{JJ}$ are dyadic tensors.^ As odd as it may seem, the actual mathematical relationship between pressure, flow, and resistance is actually more complex for fluids like water than it is for electrons.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.The term $\mathbf{V} imes\mathbf{B}$ represents the convective electric field due to plasma motion.^ Cast in these terms, current is the rate of electric charge motion through a conductor.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

The resistive electric field is given by $\eta\mathbf{J}$. .The Hall electric field, which represents decoupling between ions and electrons and acts to freeze in the magnetic field to the electron fluid, is given by $\frac{\mathbf{J} imes\mathbf{B}}{ne}$.^ As odd as it may seem, the actual mathematical relationship between pressure, flow, and resistance is actually more complex for fluids like water than it is for electrons.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

The divergence of the electron pressure is given by $\frac{ abla \cdot \mathsf{P}_e}{ne}$. .The last term on the right hand side represents electron inertia.^ Notice how there are only two variable terms on the right-hand side of the equation, S and T. All the other terms on that side are constant: 2, pi, and 33,000 are all constants (they do not change in value).
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

Magnetic topology cannot be changed by the convective electric field, the Hall electric field, or an electric field due to scalar electron pressure. .However, magnetic topology can be changed by resistive effects, nongyrotropic (off-diagonal) components of the electron pressure tensor, and electron inertia.^ As odd as it may seem, the actual mathematical relationship between pressure, flow, and resistance is actually more complex for fluids like water than it is for electrons.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ REVIEW: The polarity of the voltage drop across any resistive component is determined by the direction of electron flow through it: negative entering, and positive exiting.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ A varistor is a component that changes resistance with the amount of voltage impressed across it.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

The generalized Ohm's law plays a particularly important role in magnetic reconnection.

## History

In January 1781, before Georg Ohm's work, Henry Cavendish experimented with Leyden jars and glass tubes of varying diameter and length filled with salt solution. .He measured the current by noting how strong a shock he felt as he completed the circuit with his body.^ If we have a water pump that exerts pressure (voltage) to push water around a "circuit" (current) through a restriction (resistance), we can model how the three variables interrelate.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ In addition to voltage and current, there is another measure of free electron activity in a circuit: power .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ In my circuits 1 class we spent the last day of class talking about how much current it takes to kill some one.
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

.Cavendish wrote that the "velocity" (current) varied directly as the "degree of electrification" (voltage).^ Ohm's Law is not very useful for analyzing the behavior of components like these where resistance varies with voltage and current.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ For this reason we can regard the resistance of many circuit components as a constant, with voltage and current being directly related to each other.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ In circuits where resistance varies with changes in either voltage or current, the plot of current over voltage will be nonlinear (not a straight line).
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

He did not communicate his results to other scientists at the time,[26] and his results were unknown until Maxwell published them in 1879.[27]
.Ohm did his work on resistance in the years 1825 and 1826, and published his results in 1827 as the book Die galvanische Kette, mathematisch bearbeitet (The galvanic Circuit investigated mathematically).^ When George Simon Ohm's theory of electricity was published in 1827 in his book "The Galvanic Chain, Mathematically Worked Out," it was called .
• Erroneous Predictions 18 September 2009 7:07 UTC www.foresight.org [Source type: Original source]

^ The first, and perhaps most important, relationship between current, voltage, and resistance is called Ohm's Law, discovered by Georg Simon Ohm and published in his 1827 paper, The Galvanic Circuit Investigated Mathematically .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ By observing the results of a computer simulation, a student can gain an intuitive grasp of circuit behavior without the intimidation of abstract mathematical analysis.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

[28] He drew considerable inspiration from Fourier's work on heat conduction in the theoretical explanation of his work. .For experiments, he initially used voltaic piles, but later used a thermocouple as this provided a more stable voltage source in terms of internal resistance and constant potential difference.^ Resistors, which are manufactured to provide a definite, stable value of resistance, behave very much like the plot of values seen above.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ In the above circuit, there is only one source of voltage (the battery, on the left) and only one source of resistance to current (the lamp, on the right).
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ The increase in resistance will decrease the current to the amp, as well as its supply voltage: E = I R. Voltage sources do not "compensate" by increasing current.
• VWvortex Forums: Lights dim 11 January 2010 3:30 UTC forums.vwvortex.com [Source type: General]

.He used a galvanometer to measure current, and knew that the voltage between the thermocouple terminals was proportional to the junction temperature.^ If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Electrical power is almost always measured in "watts," and it can be calculated by the formula P = IE. Electrical power is a product of both voltage and current, not either one separately.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's Law is not very useful for analyzing the behavior of components like these where resistance varies with voltage and current.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.He then added test wires of varying length, diameter, and material to complete the circuit.^ Does the wire length or circuit "shape" matter to our calculations?
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ So far, we've been analyzing single-battery, single-resistor circuits with no regard for the connecting wires between the components, so long as a complete circuit is formed.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Though the connecting wires take a convoluted path in forming a complete circuit, there are several electrically common points in the electrons' path.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

He found that his data could be modeled through the equation
$x = \frac{a}{b + l},$
where .x was the reading from the galvanometer, l was the length of the test conductor, a depended only on the thermocouple junction temperature, and b was a constant of the entire setup.^ It is worth mentioning that temperature dependence does not make a substance non-ohmic, because at a given temperature R does not vary with voltage or current (V / I = constant).
• Calculating Voltage/Temperature thresholds - BlazingPC.com 11 January 2010 3:30 UTC www.blazingpc.com [Source type: General]

^ The resistance of an Ohmic substance depends on temperature in the following way: R = L/A * P = L/A * Po(@(T-To)+1) Where ρ is the resistivity, L is the length of the conductor, A is its cross-sectional area, T is its temperature, T0 is a reference temperature (usually room temperature), and ρ0 and α are constants specific to the material of interest.
• Calculating Voltage/Temperature thresholds - BlazingPC.com 11 January 2010 3:30 UTC www.blazingpc.com [Source type: General]

.From this, Ohm determined his law of proportionality and published his results.^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ With wire resistance being zero, the voltage drop across any continuous stretch of wire can be determined through Ohm's Law as such: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Ohm's law was probably the most important of the early quantitative descriptions of the physics of electricity.^ There are other mathematical principles of electricity that do take polarity into account through the use of signs (+ or -), but not Ohm's Law.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ The first, and perhaps most important, relationship between current, voltage, and resistance is called Ohm's Law, discovered by Georg Simon Ohm and published in his 1827 paper, The Galvanic Circuit Investigated Mathematically .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ I am probably incorrect with my point about it being an oversimplification to rely on Ohm's Law while using nominal values, to summarize the toddler mouth-burns.
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

We consider it almost obvious today. .When Ohm first published his work, this was not the case; critics reacted to his treatment of the subject with hostility.^ When George Simon Ohm's theory of electricity was published in 1827 in his book "The Galvanic Chain, Mathematically Worked Out," it was called .
• Erroneous Predictions 18 September 2009 7:07 UTC www.foresight.org [Source type: Original source]

They called his work a "web of naked fancies"[29] and the German Minister of Education proclaimed that "a professor who preached such heresies was unworthy to teach science."[30] The prevailing scientific philosophy in Germany at the time, led by Hegel, asserted that experiments need not be performed to develop an understanding of nature because nature is so well ordered, and that scientific truths may be deduced through reasoning alone. Also, Ohm's brother Martin, a mathematician, was battling the German educational system. These factors hindered the acceptance of Ohm's work, and his work did not become widely accepted until the 1840s. Fortunately, Ohm received recognition for his contributions to science well before he died.
In the 1850s, Ohm's law was known as such, and was widely considered proved, and alternatives such as "Barlow's law" discredited, in terms of real applications to telegraph system design, as discussed by Samuel F. B. Morse in 1855.[31]
.While the old term for electrical conductance, the mho (the inverse of the resistance unit ohm), is still used, a new name, the siemens, was adopted in 1971, honoring Ernst Werner von Siemens.^ Ohm's Law is not very useful for analyzing the behavior of components like these where resistance varies with voltage and current.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's Law is a very simple and useful tool for analyzing electric circuits.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Each unit of measurement is named after a famous experimenter in electricity: The amp after the Frenchman Andre M. Ampere, the volt after the Italian Alessandro Volta, and the ohm after the German Georg Simon Ohm.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

The siemens is preferred in formal papers.
.In the 1920s, it was discovered that the current through an ideal resistor actually has statistical fluctuations, which depend on temperature, even when voltage and resistance are exactly constant; this fluctuation, now known as Johnson–Nyquist noise, is due to the discrete nature of charge.^ Then it displays the current through each voltage source.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ How voltage, current, and resistance relate .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ As the current encounters the 5 Ω resistance, voltage is dropped across the resistor's ends.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.This thermal effect implies that measurements of current and voltage that are taken over sufficiently short periods of time will yield ratios of V/I that fluctuate from the value of R implied by the time average or ensemble average of the measured current; Ohm's law remains correct for the average current, in the case of ordinary resistive materials.^ Calculation of Ohm's law · The Magic Triangle Calculation of electric power, voltage, current and resistance .
• Backlinks to www.sengpielaudio.com back links - Mikrofonaufnahme und Tonstudiotechnik Some Back Links - Senkpiel ist immer Sengpiel - sengpielaudio Eberhard Sengpiel Berlin 11 January 2010 3:30 UTC www.sengpielaudio.com [Source type: FILTERED WITH BAYES]

^ How voltage, current, and resistance relate .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Here are the standard units of measurement for electrical current, voltage, and resistance: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Ohm's work long preceded Maxwell's equations and any understanding of frequency-dependent effects in AC circuits.^ However, these power equations are so commonly associated with the Ohm's Law equations relating voltage, current, and resistance (E=IR ; I=E/R ; and R=E/I) that they are frequently credited to Ohm.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Modern developments in electromagnetic theory and circuit theory do not contradict Ohm's law when they are evaluated within the appropriate limits.^ I didn't say that Ohms Law is a theory.
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

^ Resistor values in ohms are usually shown as an adjacent number, and if several resistors are present in a circuit, they will be labeled with a unique identifier number such as R 1 , R 2 , R 3 , etc.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Electronic circuits can display highly complex behaviors, even though they are governed by the same laws as simple electrical circuits.
• Calculating Voltage/Temperature thresholds - BlazingPC.com 11 January 2010 3:30 UTC www.blazingpc.com [Source type: General]

## References

1. ^ Consoliver, Earl L., and Mitchell, Grover I. (1920). Automotive ignition systems. McGraw-Hill. p. 4.
2. ^ a b Robert A. Millikan and E. S. Bishop (1917). Elements of Electricity. American Technical Society. p. 54.
3. ^ Oliver Heaviside (1894). Electrical papers. 1. Macmillan and Co. p. 283.
4. ^ Olivier Darrigol, Electrodynamics from Ampère to Einstein, p.70, Oxford University Press, 2000 ISBN 0198505949.
5. ^ Drude, Paul (1900). "Zur Elektronentheorie der metalle". Annalen der Physik 306 (3): 566.
6. ^ Drude, Paul (1900). "Zur Elektronentheorie der Metalle; II. Teil. Galvanomagnetische und thermomagnetische Effecte". Annalen der Physik 308 (11): 369.
7. ^ Normal Lockyer, ed (Sept. 21, 1876). "Reports". Nature (Macmillan Journals Ltd) 14: 452.
8. ^ A. Akers, M. Gassman, & R. Smith (2006). Hydraulic Power System Analysis. New York: Taylor & Francis. Chapter 13. ISBN 0-8247-9956-9.
9. ^ A. Esposito, "A Simplified Method for Analyzing Circuits by Analogy", Machine Design, October 1969, pp. 173–177.
10. ^ James William Nilsson and Susan A. Riedel (2008). Electric circuits. Prentice Hall. p. 29. ISBN 9780131989252.
11. ^ Alvin M. Halpern and Erich Erlbach (1998). Schaum's outline of theory and problems of beginning physics II. McGraw-Hill Professional. p. 140. ISBN 9780070257078.
12. ^ Dale R. Patrick and Stephen W. Fardo (1999). Understanding DC circuits. Newnes. p. 96. ISBN 9780750671101.
13. ^ Thomas O'Conor Sloane (1909). Elementary electrical calculations. D. Van Nostrand Co. p. 41.
14. ^
15. ^ Benjamin Stein (1997). Building technology (2nd ed.). John Wiley and Sons. p. 169. ISBN 9780471593195.
16. ^
17. ^ Hughes, E, Electrical Technology, pp10, Longmans, 1969.
18. ^ Forbes T. Brown (2006). Engineering System Dynamics. CRC Press. p. 43. ISBN 9780849396489.
19. ^ Kenneth L. Kaiser (2004). Electromagnetic Compatibility Handbook. CRC Press. p. 13–52. ISBN 9780849320873.
20. ^ Horowitz, Paul; Winfield Hill (1989). The Art of Electronics (2nd ed.). Cambridge University Press. p. 13. ISBN 0-521-37095-7.
21. ^ Lerner, Lawrence S. (1977). Physics for scientists and engineers. Jones & Bartlett. p. 736. ISBN 9780763704605.
22. ^ Seymour J, Physical Electronics, Pitman, 1972, pp 53–54
23. ^ Lerner L, Physics for scientists and engineers, Jones & Bartlett, 1997, pp. 685–686
24. ^ a b Lerner L, Physics for scientists and engineers, Jones & Bartlett, 1997, pp. 732–733
25. ^ Seymour J, Physical Electronics, pp 48–49, Pitman, 1972
26. ^ "Electricity". Encyclopedia Britannica. 1911.
27. ^ Sanford P. Bordeau (1982) Volts to Hertz...the Rise of Electricity. Burgess Publishing Company, Minneapolis, MN. pp.86–107, ISBN 0-8087-4908-0
28. ^ G. S. Ohm (1827). Die galvanische Kette, mathematisch bearbeitet. Berlin: T. H. Riemann.
29. ^ Davies, B, "A web of naked fancies?", Physics Education 15 57–61, Institute of Physics, Issue 1, Jan 1980 [1]
30. ^ Hart, IB, Makers of Science, London, Oxford University Press, 1923. p. 243. [2]
31. ^ Taliaferro Preston (1855). Shaffner's Telegraph Companion: Devoted to the Science and Art of the Morse Telegraph. Vol.2. Pudney & Russell.

.

# Study guide

Up to date as of January 14, 2010

### From Wikiversity

What is the voltage (V) across a circuit with resistance = R and current = I?

## Contents

### Purpose

.Understand Ohm's law in the context of electronics, and the meaning of Voltage, Current, and Resistance in the law.^ Ohm's Law a fundamental principle in electronics.
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

^ With current steady, voltage follows resistance (an increase in resistance means an increase in voltage).
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohms Law Calculator provides the best way to calculate Voltage, Current, Resistance and Power.
• Ohms Law Calculator for WM 5.0/6.0 1.0 Windows Mobile Pocket PC 18 September 2009 7:07 UTC www.mobiletopsoft.com [Source type: General]

### The Law

This law is usually stated as
$V = I \cdot R$
Voltage = Current multiplied by Resistance
It may be alternatively stated as
$E = I \cdot R$
Electromotive Force = Current multiplied by Resistance
.Although the meanings are the same, the different notation exists.^ Although the meanings are the same, the different notation exists.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ The same equation describes both phenomena, the equation's variables taking on different meanings in the two cases.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.
Based on the work of Georg Simon Ohm, Ohm's law is one of three fundamental laws which begin the study of electronics, in partnership with Kirchhoff's voltage and current laws.
^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ Ohm's Law a fundamental principle in electronics.
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

^ The current and voltage equations are determined from Kirchhoff's laws .
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

.These three laws form the frame on which the rest of electronics is constructed.^ These three laws form the frame on which the rest of electronics is constructed.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ Ohms law describes the fundamental relationship between the three most important measurements in electronics, Voltage (E), Current (I) and Resistance (R).

^ It's important to note that these laws don't apply everywhere, but definitely apply with great precision in wires, which are used to connect most electronic parts together in a circuit.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

.It's important to note that these laws don't apply everywhere, but definitely apply with great precision in wires, which are used to connect most electronic parts together in a circuit.^ It's important to note that these laws don't apply everywhere, but definitely apply with great precision in wires, which are used to connect most electronic parts together in a circuit.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ In this article I will review the definitions of these three properties of an electrical circuit, the relationship between them described by Ohm's Law,  and offer some practical considerations to keep in mind when using Ohm's Law to calculate unknown quantities in an electrical circuit.
• How to Use Ohm's Law for Voltage, Current and Resistance - Associated Content - associatedcontent.com 11 January 2010 3:30 UTC www.associatedcontent.com [Source type: General]

^ Though computers running electronic computer-aided design and analysis programs do the bulk of the work predicting and optimizing the performance of electrical circuits, most electrical engineers still use Ohm's law every working day.
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

.Though individual parts may or may not be analysed by Ohm's law, their relationship to the circuit can be.^ Though individual parts may or may not be analysed by Ohm's law, their relationship to the circuit can be.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ Would something like "Though Ohm's law is not applicable to all circuit parts, .."
• Talk:Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ I've been correcting some of the spelling on this entry (hope you dont mind) and the sentence "Though individual parts may or may not be analysed by Ohm's law, their relationship to the circuit can be."
• Talk:Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

.Any student completing a course in electronics should be capable of quoting Ohm's law in his or her sleep.^ Ohm's Law a fundamental principle in electronics.
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

^ Any student completing a course in electronics should be capable of quoting Ohm's law in his or her sleep.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ Electronic materials such as those based on semiconductors play an increasing role and are non-ohmic: they do not obey Ohm's Law.

.Not because they learn it once, but because it's used repeatedly in conjunction with almost every other task in electronics.^ Not because they learn it once, but because it's used repeatedly in conjunction with almost every other task in electronics.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ Because even before you apply the voltage to the circuit the wires are filled with electrons (but they dont have a directional movement yet).
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

^ Put them in series, and they will all illuminate, but dimly, because each lightbulb adds resistance to the circuit, one right after the other.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

.The actual statement of Ohm's Law is: The current flowing through a metallic conductor is proportional to the Electromotive force applied across it's ends, provided the temperature and all other conditions remain constant.^ Current I The rate of flow of electricity through a conductor, measured in Amperes.
• Ohms Law Electronics Calculator - CalcResult Electrical Calculators 18 September 2009 7:07 UTC www.calcresult.com [Source type: FILTERED WITH BAYES]

^ The actual statement of Ohm's Law is: The current flowing through a metallic conductor is proportional to the Electromotive force applied across it's ends, provided the temperature and all other conditions remain constant.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ The law states the relationship between electromotive force, current and resistance.
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

.Note there is no mention of resistance; that is simply the name given to the constant of proportionality involved.^ Note there is no mention of resistance; that is simply the name given to the constant of proportionality involved.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ The relation V / I = R even holds also for non-ohmic devices, but then the resistance R depends on V and is no longer a constant.
• Georg Simon Ohm: The Discovery of Ohm's Law 18 September 2009 7:07 UTC www.juliantrubin.com [Source type: Academic]

^ Den, on 10/03/2009 , -0/+1 "If you send a constant V and I " You can't send a constant V and I. I is the result of Ohm's law - so for any given V, I will depend on the resistance of the light bulb.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

Something important to take away from this definition is
• In a passive circuit, the current is a result of the voltage applied
and
• there are definite thermal effects on the resistance (or effective resistance) of conductors.
.Ohm's law is linear and therefore assumes linearity in the electronic part.^ Ohm's Law a fundamental principle in electronics.
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

^ Ohm's law is linear and therefore assumes linearity in the electronic part.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ Electronic materials such as those based on semiconductors play an increasing role and are non-ohmic: they do not obey Ohm's Law.

.It's easy to think of the law in terms of the line equation y = mx considering resistance to be the constant m, current as the independent variable x, and voltage as the dependent variable y.^ It's easy to think of the law in terms of the line equation y = m x considering resistance to be the constant m, current as the independent variable x, and voltage as the dependent variable y.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ Ohm found that the current in a circuit varies directly with the voltage when the resistance is constant.

^ Once again, the current and voltage equations are determined from Kirchhoff's laws.
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

.In this way a proportionate relationship between voltage and current is established.^ Bavaria, defines the relationship between power, voltage, current and resistance.

^ Bavaria, defines the relationship between power, voltage , current and resistance .

^ In this way a proportionate relationship between voltage and current is established.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

.Of course, Ohm's law may be rearranged in three valid and easily derivable ways.^ Of course, Ohm's law may be rearranged in three valid and easily derivable ways.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ Of course, Ohms Law can be rearranged to solve for either current or voltage.

.It's important to be familiar with each of these and comfortable in recognising and switching between them.^ It's important to be familiar with each of these and comfortable in recognising and switching between them.
• Ohm's law - Wikiversity 11 January 2010 3:30 UTC en.wikiversity.org [Source type: Original source]

^ These units and symbols for electrical quantities will become very important to know as we begin to explore the relationships between them in circuits.
• How voltage, current, and resistance relate : OHM's LAW 18 September 2009 7:07 UTC www.allaboutcircuits.com [Source type: FILTERED WITH BAYES]
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

$V = I \cdot R$
$I = \frac{V}{R}$
$R = \frac{V}{I}$
Example:
If you have one amp (1A) of current flowing through a 2 ohm resistor, how much voltage will be across it?
 1 volt Try again using Ohm's law 2 volts Correct, I=1, R=2, I*R=V 1/2 a volt .Try again, did you switch current and voltage?^ Written as a mathematical expression, Ohms Law is Resistance(R)=voltage(V)/current(I) or R=V/I The above equation allows you to determine the value of the resistance when the voltage and the current are known. Ohms Law - Electronic Circuits Projects Diagrams Free 18 September 2009 7:07 UTC www.electro-tech-online.com [Source type: General] ^ If we were to plot current over voltage on a graph as we did with the lamp circuit, the effect of ionization would be clearly seen as nonlinear: . Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES] ^ Did you try the "Plug a light in the same socket" part yet? Electricity FUBAR question [Archive] - Quarter To Three Forums 11 January 2010 3:30 UTC www.quartertothree.com [Source type: Original source] 3 volts Try again, do not add them together, use I*R=V
.OHM'S LAW- The current in an electric circuit is directly proportional to the electromotive force in the circuit the most common form of the law is E=IR, where E is the electromotive force of voltage across the circuit, I is the current flowing in the circuit and R is the resistance if the circuit.^ The 'conductor' mentioned by Ohm's law is a circuit element across which the voltage is measured.
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

^ With little voltage across it, its resistance is high.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Poor grounds cause resistance, which REDUCES current flow and voltages.
• VWvortex Forums: Lights dim 11 January 2010 3:30 UTC forums.vwvortex.com [Source type: General]

### Understanding Voltage, Current, and Resistance

#### Water Flow Analogy

.Electrons flow through wires like water flowing through pipes.^ Voltage is like the size of the pipe, amps are like the pressure of water through the pipe.
• Electricity FUBAR question [Archive] - Quarter To Three Forums 11 January 2010 3:30 UTC www.quartertothree.com [Source type: Original source]

^ Putting resistors in parallel is like adding lanes to a highway - more traffic (current aka amps) can flow through faster.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ The flow of particles through a reference surface as symbolized by one of arrows above, say the arrow in the + x -direction, must be seen as an average over the x - component of the velocity of the individual particles in the wire.
• Ohms Law and Materials Properties 18 September 2009 7:07 UTC www.tf.uni-kiel.de [Source type: FILTERED WITH BAYES]

.Understanding the similarity helps one begin to appreciate voltage, current, and resistance in the context of Ohm's law.^ That's one of three values in Ohm's Law.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

^ Dividing voltage by current gives resistance, .
• Amateur Radio Manual/Ohm's Law and Resistors - Wikibooks, collection of open-content textbooks 11 January 2010 3:30 UTC en.wikibooks.org [Source type: FILTERED WITH BAYES]

^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Fortunately, calculating current flow using Ohm's law is easier than water flow, because Ohm's law is linear while the laws governing water flow, are not.^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Calculate the current flow?
• Untitled Document 18 September 2009 7:07 UTC okragraphics.com [Source type: Academic]

^ A similar assumption is made in the statement of Ohm's law: other things being alike, the strength of the current at each point is proportional to the gradient of electric potential.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.By imagining water flowing out of a water tower to some destination, it's clear that the weight of the water at the top of the tower pushes all of the water through the pipes to it's various destinations.^ We say that the rate of water flow through an aperture restrictor is proportional to the difference in water pressure across the restrictor.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ This continuous movement of free electrons through the conductors of a circuit is called a current , and it is often referred to in terms of "flow," just like the flow of a liquid through a hollow pipe.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ The pressure is equal upon all 3 pipes but the one of least resistance will take in the majority of water, leaving only a little water to flow through the other 2 pipes, resulting in low resistance overall.
• Total Resistence in Parallel circuit - All About Circuits Forum 11 January 2010 3:30 UTC forum.allaboutcircuits.com [Source type: General]

.In this example, the water can't flow as fast through all of the pipes as others, because the pipes aren't equal.^ We say that the rate of water flow through an aperture restrictor is proportional to the difference in water pressure across the restrictor.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

^ This continuous movement of free electrons through the conductors of a circuit is called a current , and it is often referred to in terms of "flow," just like the flow of a liquid through a hollow pipe.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Put them in series, and they will all illuminate, but dimly, because each lightbulb adds resistance to the circuit, one right after the other.
• www.TK560.com :: View topic - Question about the voltage calculator. 11 January 2010 3:30 UTC www.tk560.com [Source type: General]

.Some pipes are really skinny, others go up hills, and some are filled with unsightly gunk.^ He is not implying that electrons find that they cannot go one way, so they back up and go the other.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

^ Some districts take the easy route to fill their "quotas" by just setting up in a road that is really not that really does not have any records of road deaths and they will catch out drivers for a number of years.
• crap economy? watch your speed guys [Archive] - Steam Users' Forums 11 January 2010 3:30 UTC forums.steampowered.com [Source type: Original source]

^ Ohm%27s_law It's not much simplier than that though I'm not asserting that other factors may not necessarily involved, but go ahead and argue some more.
• Nikon ML-3 wireless remote review [Archive] - Digital Camera Resource Page Forums 11 January 2010 3:30 UTC www.dcresource.com [Source type: General]

.Notwithstanding all of the causes of resistance in the pipes, one can imagine that the harder the water is pushed, the faster it's going to flow in the pipes.^ The phenomenon of resistance changing with variations in temperature is one shared by almost all metals, of which most wires are made.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Poor grounds cause resistance, which REDUCES current flow and voltages.
• VWvortex Forums: Lights dim 11 January 2010 3:30 UTC forums.vwvortex.com [Source type: General]

^ The pressure is equal upon all 3 pipes but the one of least resistance will take in the majority of water, leaving only a little water to flow through the other 2 pipes, resulting in low resistance overall.
• Total Resistence in Parallel circuit - All About Circuits Forum 11 January 2010 3:30 UTC forum.allaboutcircuits.com [Source type: General]

.Voltage, denoted by V (and sometimes "w", representing electromotive force), is the push of electrons through a wire, and is measured in volts.^ Voltage is EMF, or electromotive force.
• Electricity FUBAR question [Archive] - Quarter To Three Forums 11 January 2010 3:30 UTC www.quartertothree.com [Source type: Original source]

^ The potential difference is also known as the voltage drop, and is sometimes denoted by U, E or emf (electromotive force) instead of V.[1] The law was named after the physicist Georg Ohm, who, in a treatise published in 1827, described measurements of applied voltage and current passing through simple electrical circuits containing various lengths of wire.
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

^ In the following equations, V is voltage measured in volts, I is current measured in amperes and R is resistance measured in ohms : V = I x R R = V / I I = V / R Knowing any two of the values of a circuit, one can determine the third using Ohms Law.
• Ohms Law - Internetnews.com - Webopedia.com 18 September 2009 7:07 UTC inews.webopedia.com [Source type: General]
• Ohms Law - Inside ID Online Glossary of Identity Management Terminology 18 September 2009 7:07 UTC insideid.webopedia.com [Source type: FILTERED WITH BAYES]

.When voltage is applied to a wire it would be unwise to simply touch it, but without voltage the wire would be harmless.^ Because even before you apply the voltage to the circuit the wires are filled with electrons (but they dont have a directional movement yet).
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

^ Likewise, if we were to have a short circuit constructed of a loop of superconducting wire (absolutely zero resistance), we could have a condition of current in the loop with zero voltage, and likewise no power would be dissipated.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ If what you say is true, that would indicate a higher voltage (unless the cable tip was overloading the current, and she also touched the hot tip with her finger).
• Toddler gets shocked with the USB Ipod charger 11 January 2010 3:30 UTC digg.com [Source type: General]

.In the water flow analogy voltage is analogous to the weight of water in the tower pushing down through all the pipes.^ Georg Ohm found that, at a constant temperature, the electrical current flowing through a fixed linear resistance is directly proportional to the voltage applied across it, and also inversely proportional to the resistance.

^ Then ran the low voltage control/eye wires down the center of the pipe out of sight.
• Bulb for garage door opener - dslreports.com 11 January 2010 3:30 UTC www.dslreports.com [Source type: General]

^ According to Ohm's law (V=IR), in the diagram below, electrons flow through the wire and when they are at point A they all turn right following the green arrow.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

.Current, denoted by I, is the flow of electrons through a wire, and is measured in amperes, denoted by A. Current is caused by voltage, and is not to be confused with voltage.^ Ohm varied the voltage across the resistance and measured the current through it.

^ Then it displays the current through each voltage source.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Georg Ohm found that, at a constant temperature, the electrical current flowing through a fixed linear resistance is directly proportional to the voltage applied across it, and also inversely proportional to the resistance.

.When doing calculations with Ohm's law the cause and effect of voltage and current is not apparent, but remembering the basic cause and effect will prevent confusion.^ Using Ohm's Law to determine current, we get: .
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Ohm's Law Circle helpful in remembering the calculations that can be made.
• MATHS can any 1 help me with ohms law? - Yahoo! UK & Ireland Answers 11 January 2010 3:30 UTC uk.answers.yahoo.com [Source type: General]

^ Calculation of Ohm's law · The Magic Triangle Calculation of electric power, voltage, current and resistance .
• Backlinks to www.sengpielaudio.com back links - Mikrofonaufnahme und Tonstudiotechnik Some Back Links - Senkpiel ist immer Sengpiel - sengpielaudio Eberhard Sengpiel Berlin 11 January 2010 3:30 UTC www.sengpielaudio.com [Source type: FILTERED WITH BAYES]

.In the water flow analogy, the current is the movement of water.^ This continuous movement of free electrons through the conductors of a circuit is called a current , and it is often referred to in terms of "flow," just like the flow of a liquid through a hollow pipe.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ Jun24-06, 04:31 PM Think of the analogy of water flowing in pipes.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

^ Jun24-06, 05:23 PM In the correct water flow analogy of the electric current the pipes are always filled with water from the beginning.
• Do electrons think? [Archive] - Physics Forums 11 January 2010 3:30 UTC www.physicsforums.com [Source type: Original source]

.Water flow rate may be expressed as some volume of water per time.^ You may also consider getting a surge suppressor strip (a good one) that will help even out some of the peaks and valleys of power flow.
• Bulb for garage door opener - dslreports.com 11 January 2010 3:30 UTC www.dslreports.com [Source type: General]

^ If the resistance to water flow stays the same and the pump pressure increases, the flow rate must also increase.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ We say that the rate of water flow through an aperture restrictor is proportional to the difference in water pressure across the restrictor.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

.Likewise the measure of current, the ampere, can be defined in terms of a quantity of electrons per time.^ In the following equations, V is voltage measured in volts, I is current measured in amperes and R is resistance measured in ohms : V = I x R R = V / I I = V / R Knowing any two of the values of a circuit, one can determine the third using Ohms Law.
• Ohms Law - Internetnews.com - Webopedia.com 18 September 2009 7:07 UTC inews.webopedia.com [Source type: General]
• Ohms Law - Inside ID Online Glossary of Identity Management Terminology 18 September 2009 7:07 UTC insideid.webopedia.com [Source type: FILTERED WITH BAYES]

^ The mathematical equation that describes this relationship is: where I is the current in amperes, V is the potential difference between two points of interest in volts, and R is a circuit parameter, measured in ohms (which is equivalent to volts per ampere), and is called the resistance.
• What is ohms law.? - Yahoo! Answers 11 January 2010 3:30 UTC answers.yahoo.com [Source type: FILTERED WITH BAYES]

^ This continuous movement of free electrons through the conductors of a circuit is called a current , and it is often referred to in terms of "flow," just like the flow of a liquid through a hollow pipe.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Resistance, denoted by R, slows or resists the electron flow in a wire, and is measured in ohms, denoted by the Greek letter for omega (Ω).^ The letter for resistance is R and is expressed in ohms.
• MATHS can any 1 help me with ohms law? - Yahoo! UK & Ireland Answers 11 January 2010 3:30 UTC uk.answers.yahoo.com [Source type: General]

^ Resistance measured in ohms , symbolized by the letter "R".
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ In the following equations, V is voltage measured in volts, I is current measured in amperes and R is resistance measured in ohms : V = I x R R = V / I I = V / R Knowing any two of the values of a circuit, one can determine the third using Ohms Law.
• Ohms Law - Internetnews.com - Webopedia.com 18 September 2009 7:07 UTC inews.webopedia.com [Source type: General]
• Ohms Law - Inside ID Online Glossary of Identity Management Terminology 18 September 2009 7:07 UTC insideid.webopedia.com [Source type: FILTERED WITH BAYES]

.Resistance is caused by anything and everything in a wire, but it is all simply measured in ohms.^ Resistance measured in ohms , symbolized by the letter "R".
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

^ In the following equations, V is voltage measured in volts, I is current measured in amperes and R is resistance measured in ohms : V = I x R R = V / I I = V / R Knowing any two of the values of a circuit, one can determine the third using Ohms Law.
• Ohms Law - Internetnews.com - Webopedia.com 18 September 2009 7:07 UTC inews.webopedia.com [Source type: General]

^ I was concerned that a student/newbie would think he could use a ohm meter etc, to measure the 'resistance' of his semi's.
• Ohms Law - Page 2 - Electronic Circuits Projects Diagrams Free 18 September 2009 7:07 UTC www.electro-tech-online.com [Source type: Original source]

.In the water flow analogy the resistance is caused by the restriction in pipes, hills, and unsightly dark matter.^ Poor grounds cause resistance, which REDUCES current flow and voltages.
• VWvortex Forums: Lights dim 11 January 2010 3:30 UTC forums.vwvortex.com [Source type: General]

^ The pressure is equal upon all 3 pipes but the one of least resistance will take in the majority of water, leaving only a little water to flow through the other 2 pipes, resulting in low resistance overall.
• Total Resistence in Parallel circuit - All About Circuits Forum 11 January 2010 3:30 UTC forum.allaboutcircuits.com [Source type: General]

^ If we have a water pump that exerts pressure (voltage) to push water around a "circuit" (current) through a restriction (resistance), we can model how the three variables interrelate.
• Lessons In Electric Circuits -- Volume I (DC) - Chapter 2 18 September 2009 7:07 UTC openbookproject.net [Source type: FILTERED WITH BAYES]

.Well, now, let us look at the formal statement: Ohm's law states that, in an electrical circuit, the current passing through a conductor is directly proportional to the potential difference applied across them under constant physical conditions.^ But on the whole, ohm's law does not apply.
• xkcd - A Webcomic - Ohm 11 January 2010 3:30 UTC digg.com [Source type: Original source]

^ The current in a circuit is directly proportional to the electric potential difference impressed across its ends and inversely proportional to the total resistance offered by the external circuit.

^ The "conductor" mentioned by Ohm's law is a circuit element across which the voltage is measured.
• Ohm's Law 11 January 2010 3:30 UTC jugandi.com [Source type: Academic]

# Wiktionary

Up to date as of January 15, 2010

## English

### Etymology

From Georg Ohm German physicist

### Noun

Wikipedia has an article on:
1. (physics) In its basic form Ohm's law states that the direct current flowing in an electrical circuit consisting only of resistances is directly proportional to the voltage applied.

# Simple English

Ohm's law says that in an electrical circuit, the current passing through a resistor between two points, is related to the voltage difference between the two points, and inversely related to the electrical conductance between the two points. This relation is shown in the following formula:

$R = \frac VI$

where I is the current in amperes, V is the potential difference in volts, and R is a constant, measured in ohms, called the resistance.

It also says that current is directly proportional to voltage loss though a resistor. That is if current doubles then so does voltage. To make a current flow through a resistance there must be a voltage across that resistance. Ohm's Law shows the relationship between the voltage (V), current (I) and resistance (R). It can be written in three ways:

# Citable sentences

Up to date as of December 19, 2010

Here are sentences from other pages on Ohm's law, which are similar to those in the above article.