Question

If potential difference across a capacitor is changed from 15 V to 30 V, work done is W. The work done when potential difference is changed from 30 V to 60 V, will be:

• A. W
• B. 4 W
• C. 3 W
• D. 2 W

Answer 1

Answer: (B)

4 W

Answer 2

From relation of work done $W=\frac{1}{2}C{{V}^{2}},$
so $W\propto {{V}^{2}}$
As ${{V}_{2}}=60-30=30\,V,$
${{V}_{1}}=30-15=15\,V$
hence $\frac{W_2}{W_1}=(\frac{V_2}{V_1})^2$ or ${{W}_{2}}={{\left( \frac{30}{15} \right)}^{2}}W$
${{W}_{1}}=W$
${{W}_{2}}=4\,W$
The correct option is (B): 4 W.