Question

A $5\mu F$ capacitor is fully charged by a $12V$ battery and then disconnected. If it is connected now parallel to an uncharged capacitor, the voltage across it is $3V$. Then, the capacity of the uncharged capacitor is

• A. $5\mu F$
• B. $25\mu F$
• C. $50\mu F$
• D. $10\mu F$
• E. $15\mu F$

Answer 1

The correct option is B $25\mu F$

Given, $C=5\mu F$
and $V=12V$
We know that, $Q=CV$
$Q=5\times 12=60\mu C$
According to the question,
$\frac{60}{C^{\prime }}=3$
$\Rightarrow C^{\prime }=20\mu F$
Net capacitance $=20+5=25\mu F$.