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A generator G charges a battery. The generator's terminal voltage is 120 V while it pushes a charging current of 10 A. The battery has emf 100 V and internal resistance 1 Ohm. To maintain a 10 A charging current, what value must the series resistance R have?

1. 1.0 Ohm
2. 0.1 Ohm
3. 0.5 Ohm
4. 5.0 Ohm

Correct answer: 1.0 Ohm

Solution

Net 20 V across (R + 1) Ohm at 10 A gives R + 1 = 2, so R = 1 Ohm.

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