# Ohm's law

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Related to Ohms Law: Kirchoff's Law

## Ohm's law

Ohm's law (ōm) [for G. S. Ohm], law stating that the electric current i flowing through a given resistance r is equal to the applied voltage v divided by the resistance, or i=v/r. For general application to alternating-current circuits where inductances and capacitances as well as resistances may be present, the law must be amended to i=v/z, where z is impedance. There are conductors in which the current that flows is not proportional to the applied voltage. These do not follow this law and are called nonohmic conductors.

## Ohm's law

The direct current flowing in an electrical circuit is directly proportional to the voltage applied to the circuit. The constant of proportionality R, called the electrical resistance, is given by the

equation below, in which V is the applied voltage and I is the current. Numerous deviations from this simple, linear relationship have been discovered. See Electrical resistance

McGraw-Hill Concise Encyclopedia of Physics. © 2002 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

## Ohm’s Law

a law that states that the steady current density I in a conductor is directly proportional to the potential difference (voltage) U between two fixed points or cross sections of the conductor:

(1) RI = U

The proportionality constant R, which depends on the geometric and electric properties of the conductor and on temperature, is called the ohmic resistance, or simply the resistance, of the given section of the conductor. Ohm’s law was discovered in 1826 by the German physicist G. S. Ohm.

In the general case, the relationship between I and U is nonlinear; however, in practice it is always possible to assume it to be linear for a certain range of voltages and to apply Ohm’s law for this range. For metals and their alloys the range is virtually unlimited.

Ohm’s law in form (1) is valid for those sections of a circuit that do not contain any sources of electromotive force (emf). If such sources (storage batteries, thermocouples, or dynamos) are present, Ohm’s law assumes the form

(2) RI= U + E

where E is the emf of all sources connected in the section of the circuit that is being considered. For a closed circuit, Ohm’s law assumes the following form:

(3) RtI = E

where Rt = R + Ri is the total resistance of the entire circuit, which is equal to the sum of the external resistance R of the circuit and the internal resistance Ri of the source of emf. Kirchhoff’s laws generalize Ohm’s law for the case of branched circuits.

Ohm’s law can also be written in differential form, which links the current density j and the total electric field strength for each point of the conductor. The potential electric field of intensity E generated in conductors by the microscopic charges—electrons and ions—of the conductors themselves cannot support steady motion of free charges (a current), since the work done by the field in a closed loop is equal to zero. The current is supported by nonelectrostatic forces of various origins (induction, chemical, thermal, and so on) that are active in the emf sources and can be represented as some equivalent, nonpotential field of intensity Eext, called the external field. In the general case, the total strength of the field acting on the charges in the conductor is E + Eext. Correspondingly, the differential Ohm’s law assumes the form

(4) ρj = E + Eext or j = σ(E + Eext)

where ρ is the specific electric resistivity of the conductor material and σ = 1/ρ is the specific electrical conductivity.

Ohm’s law in complex form is also valid for sinusoidal quasi-stationary currents:

(5) ZI = E

where Z is the total complex impedance, equal to R + iX, and R and iX are the resistance and reactance of the circuit, respectively. If an inductance L and a capacitance C are present in a circuit carrying a quasi-stationary current of frequency ω, then X= ωL - 1/ωC.

### REFERENCES

Kursfiziki, vol. 2. Edited by N. D. Papaleksi. Moscow-Leningrad, 1948.
Kalashnikov, S. G. Elektrichestvo. Moscow, 1964. (Obshchii kurs fiziki, vol. 2.)
Fizicheskie osnovy elektrotekhniki. General editor, K. M. Polivanov. Moscow-Leningrad, 1950.

## Ohm's law

[′ōmz ‚lȯ]
(electricity)
The law that the direct current flowing in an electric circuit is directly proportional to the voltage applied to the circuit; it is valid for metallic circuits and many circuits containing an electrolytic resistance.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## Ohm's law

The direct current flowing in an electrical circuit is directly proportional to the voltage applied to the circuit. The constant of proportionality R, called the electrical resistance, is given by the

equation below, in which V is the applied voltage and I is the current. Numerous deviations from this simple, linear relationship have been discovered.

McGraw-Hill Concise Encyclopedia of Engineering. © 2002 by The McGraw-Hill Companies, Inc.

## Ohm’s law

A law stating that the current in an electric circuit is directly proportional to the electromotive force (voltage) in the circuit and inversely proportional to the resistance in the circuit.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

## ohm

The unit of measurement of electrical resistance in a material. One ohm is the resistance in a circuit when one volt maintains a current of one amp. The symbol for ohm is the Greek letter omega. See impedance.

Ohm's Law
The equation "R=V/I" is the more streamlined version of the one developed by German physicist Georg Simon Ohm in 1827. Ohm's law is used to calculate the resistance in materials such as metal, which maintain a linear relationship between voltage and current. In addition, Ohm's formulas, which are derived from Ohm's Law, are used to calculate voltage and current if the other two measurements are known.
```OHM'S LAWwResistance = voltage divided by current

R = V / I   or   R = E / I

OHM'S FORMULASVoltage = current times resistance

V = I * R   or   E = I * R

Current = voltage divided by resistance

I = V / R   or   I = E / R

V or E = voltage (E=energy)
I = current in amps (I=intensity)
R = resistance in ohms

Electric PowerPower in watts = voltage times current

P = V * I
```
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