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In a potentiometer, the primary circuit carries a current of 0.2 A. The wire has resistivity 4 x 10⁻⁷ ohm.m and cross-sectional area 8 x 10⁻⁷ m². Calculate the potential gradient along the wire.

1. 0.2 V/m
2. 1 V/m
3. 0.5 V/m
4. 0.1 V/m

Correct answer: 0.1 V/m

Solution

Resistance per metre = rho/A = (4e-7)/(8e-7) = 0.5 ohm/m; times the current 0.2 A gives 0.1 V/m.

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