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The internal resistance of a 2.1 V cell which gives a current of 0.2 A through a resistance of 10 Ω is

1. 0.5 Ω
2. 0.8 Ω
3. 1.0 Ω
4. 0.2 Ω

Correct answer: 0.5 Ω

Solution

Using Ohm's Law, the total resistance in the circuit is R_total = V/I = 2.1/0.2 = 10.5 Ω. The external resistance is 10 Ω, so the internal resistance is R_internal = R_total - R_external = 10.5 - 10 = 0.5 Ω.

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