# electrical resistance

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Related to Electric resistnace: Ohm's law, electric resistance welding

## Electrical resistance

Opposition of a circuit to the flow of electric current. Ohm's law states that the current *I* flowing in a circuit is proportional to the applied potential difference *V*. The constant of proportionality is defined as the resistance *R*. Hence, Eq. (1)

(1)

holds. If *V*and

*I*are measured in volts and amperes, respectively,

*R*is measured in ohms. Microscopically, resistance is associated with the impedance to flow of charge carriers offered by the material. For example, in a metallic conductor the charge carriers are electrons moving in a polycrystalline material in which their journey is impeded by collisions with imperfections in the local crystal lattice, such as impurity atoms, vacancies, and dislocations. In these collisions the carriers lose energy to the crystal lattice, and thus Joule heat is liberated in the conductor, which rises in temperature. The Joule heat

*P*is given by

(2)

Eq. (2). *See*Crystal defects, Electrical resistivity, Joule's law, Ohm's law

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

## electrical resistance

[i′lek·trə·kəl ri′zis·təns] (acoustics)

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

## electrical resistance

The physical property of a device, conductor, element, branch, or system, by virtue of which power is lost as heat when current flows through it; the physical property which an electric conductor exhibits to the flow of current; measured in ohms.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.