Laws of Electrical Resistance

The resistance R offered by a conductor depends on the following factors:

(1) It varies directly as its length, l.
(2) It varies inversely as the cross-section A of the conductor.
(3) It depends on the nature of the material.
(4) It also depends on the temperature of the conductor.

Neglecting the last factor for the time being, we can say that.

R∝lA or R=ρlA  _ _ _ _ _ _ _ _ (i)

where p is a constant depending on the nature of the material of the conductor and is known as its specific resistance or resistivity.

If in Eq. (i), we put , l = 1 meter and A = 1 ${\mathrm{meter}}^{}$ then R=ρ (fig 2)

Hence, specific resistance of a material may be defined as the resistance between the opposite faces of a metre cube of that material.

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