# Resistors in series and parallel; power

### Explanation of question 9

In Fig. 3.2, the value of resistance R, such that the current from the supply will be 0.5 A, must be

1. 1
2. 12
3. 24
4. 48

The answer is :- 4

Total applied p.d. = 12 V, and total current = 0.5 A, therefore, totla resistance = 12 / 0.5 = 24

Resistance of parallell combination = 24 - 12 = 12

Hence

16R
16+R

= 12,

so 4R / (16+R) = 3

therefore 4R = 48 + 3R, and R = 48

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