Question

Two capacitators having capacitances $C_1$ and $C_2$ are charged with $120V$ and $200V$ batteries respectively. When they are connected in parallel now, it is found that the potential on each one of them is zero. Then:

• A. $8C_1=5C_2$
• B. $9C_1=5C_2$
• C. $3C_1=5C_2$
• D. $5C_1=3C_2$

Answer 1

Answer: (C)

$3C_1=5C_2$

On capacitor $C_1$ charge $Q_1=C_1{V}_1=120C_1$

On capacitor $C_2$ charge $Q_2=C_2{V}_2=200C_2$

When connected in parallel, potential across each capacitor is zero. Thus charge across each capacitor is zero.

Hence charges on capacitors must be equal such that when connected in opposite polarities, net charge becomes zero.

$⟹120C_1=200C_2$

$⟹3C_1=5C_2$