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In a potentiometer setup, the galvanometer shows no deflection when the cell's terminals are balanced against 52 cm of the wire. When the same cell is shunted with a 5 ohm resistor, the new balance length becomes 40 cm. Determine the internal resistance of the cell.

1. 1.5 Ω
2. 2 Ω
3. 2.5 Ω
4. 1 Ω

Correct answer: 1.5 Ω

Solution

The internal resistance is found from r = R*(l1/l2 - 1) = 5*(52/40 - 1) = 1.5 ohm.

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