# Resistors in series and parallel; power

### Explanation of question 15

A battery has an e.m.f. of 12V and an internal resistance of 2. The maximum power that can be taken from the battery is

1. 18W
2. 36W
3. 72W
4. 144W

The answer is :- 1

For maximum power, load resistance equals internal resistance of battery, i.e. 2.

Total resistance of circuit = 2 + 2 = 4

Current I = 12 / 4 = 3 A.

Power dissipated in load = 32 x 2 = 18 W.

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