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In a potentiometer experiment, the balancing length for the first cell of emf e1 is found to be 250 cm. After shifting the galvanometer tap so that the second cell of emf e2 is balanced, the balancing length becomes 400 cm. Find the ratio e1/e2 of the two emfs.

1. 5/3
2. 8/5
3. 4/3
4. 3/2

Correct answer: 8/5

Solution

The potential gradient is constant, so emf is proportional to balancing length; the ratio of emfs equals the ratio of their balancing lengths.

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