Question

A parallel plate capacitor is charged to a definite potential and the charging battery is disconnected. Now if the plates of capacitor are moved apart, then:

• A. the stored energy of the capacitor increases
• B. charge on the capacitor increases
• C. voltage of the capacitor increases
• D. the capacitance increases

Answer 1

Answer: (A), (C)

The correct options are
A the stored energy of the capacitor increases
C voltage of the capacitor increases

We have a capacitor (fig).

On increasing d i.e moving plates away

1) Energy: $U=\frac{1}{2}\frac{Q^2}{C}$

Since no battery is connected, so Q i.e charge remains constant and

$C=\frac{{\epsilon }_{0}A}{d}$

Since d is increasing

$⟹$ C is decreasing (1)

And thus U is also increases. Thus stored energy increases.

2) Charge remains constant since no battery.

3) Voltage: $Q=CV$

Since $Q$is same i.e constant and $C$ is decreasing from equation (1)

Thus $V$voltages increases.

4) capacitance decreases from equation (1)