Although it is temperature dependent, it can be used at a given temperature to calculate the resistance of a wire of given geometry. The factor in the resistance which takes into account the nature of the material is the resistivity. Experimentally, the dependence upon these properties is a straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as The electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made. HyperPhysics***** Electricity and magnetism Non-ohmic resistance: the electric pickle Over sizable ranges of temperature, this temperature dependence can be predicted from a temperature coefficient of resistance. The resistivity, and thus the resistance, is temperature dependent. Whether or not a material obeys Ohm's law, its resistance can be described in terms of its bulk resistivity. Although the definition above involves DC current and voltage, the same definition holds for the AC application of resistors. If the resistance is constant over a considerable range of voltage, then Ohm's law, I = V/R, can be used to predict the behavior of the material. The electrical resistance of a circuit component or device is defined as the ratio of the voltage applied to the electric current which flows through it:
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