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A cell can be balanced against 110 cm and 100 cm of potentiometer wire, respectively with and without being short circuited through a resistance of 10Ω. Its internal resistance is

1. 1.0 ohm
2. 0.5 ohm
3. 2.0 ohm
4. zero

Correct answer: 0.5 ohm

Solution

The internal resistance of the cell can be calculated using the formula r = R((l1 - l2)/l2), where l1 and l2 are the balancing lengths with and without the external resistance R. Substituting the values, r = 10((110 - 100)/100) = 0.5Ω.

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