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A 2.0 V potentiometer is used to find the internal resistance of a 1.5 V cell. With the cell's external circuit open, the balance length is 76.3 cm. When a resistor of 9.5 ohm is connected across the cell's terminals, the balance length drops to 64.8 cm. Determine the internal resistance of the cell (give the nearest integer value in ohm).

1. 1
2. 2
3. 3
4. 4

Correct answer: 2

Solution

Applying r = R*(l1 - l2)/l2 = 9.5*(76.3 - 64.8)/64.8 = 9.5*11.5/64.8 = 109.25/64.8 ~ 1.69 ohm, which rounds to 2 ohm.

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