Chapter 2

Resistance and Resistivity

John Boyd

The resistance of an electrical conductor depends on four factors, these being: (a) the length of the conductor, (b) the cross-sectional area of the conductor, (c) the type of material and (d) the temperature of the material.

Resistance, *R*, is directly proportional to length, *l*, of a conductor. For example, if the length of a piece of wire is doubled, then the resistance is doubled.

Resistance, *R*, is inversely proportional to cross-sectional area, *a*, of a conductor, i.e., *R* is proportional to 1/a. Thus, for example, if the cross-sectional area of a piece of wire is doubled, then the resistance is halved.

Since *R* is proportional to *l* and *R* is proportional to 1/a, then ...

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