Question

If the charge on a capacitor is increased by $2$ coulomb, the energy stored in it increases by $21\%$. The original charge on the capacitor is

• A. 10 C
• B. 20 C
• C. 30 C
• D. 40 C

Answer 1

Answer: (B)

20 C

Answer 2

According to question
$\frac{\frac{q_{f}^{2}}{2 C}-\frac{q_{i}^{2}}{2 C}}{\frac{q_{i}^{2}}{2 C}} \times 100=21$
and $q_{f}-q_{i}=2$
Solving, we get $q_{i}=20 \,C$.