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A potentiometer wire PQ of length 1 m is driven by a standard cell E1. A second cell E2 of EMF 1.02 V is connected in series with a resistance r and a switch S. With S open, the balance (null) point is located 49 cm from end Q. Find the potential gradient along the wire.

1. 0.02 V/cm
2. 0.04 V/cm
3. 0.01 V/cm
4. 0.03 V/cm

Correct answer: 0.02 V/cm

Solution

At null, the EMF 1.02 V equals the potential drop over the balancing length measured from P. The gradient is EMF divided by that length.

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