Physics - Capacitor Question with Solution | TestHub

Let the capacitance of each capacitor be $C$.

When four identical capacitors are connected in series across a $20\text{V}$ battery, the potential difference divides equally among them.

The potential difference across each capacitor is:

$V^{\prime }=\frac{20}{4}=5\text{V}$

The charge acquired by each capacitor is $q=C{V}^{\prime }=5C$.

When these capacitors are separated and connected in parallel (with plates of the same polarity connected together), the total charge of the system becomes:

$Q_{total}=4q=4(5C)=20C$

The equivalent capacitance of the parallel combination is:

$C_{eq}=4C$

The common potential difference across the parallel combination is:

$V_{common}=\frac{Q_{total}}{C_{eq}}=\frac{20C}{4C}=5\text{V}$

Answer: $5\text{V}$