Question

A $600 \,pF$ capacitor is charged by a $200\, V$ supply. It is then disconnected from the supply and is connected to another uncharged $600 \,pF$ capacitor. What is the common potential (in $V$) and energy lost (in $J$) after reconnection?

• A. $100,6 \times 10^{-6}$
• B. $200,6 \times 10^{-5}$
• C. $200,5 \times 10^{-6}$
• D. $100,6 \times 10^{-5}$

Answer 1

Answer: (A)

$V_{C}=\frac{C_{1} V_{1}}{C_{1}+C_{2}}=100\, V$
Energy lost $=U_{i}-U_{f}$
$=\frac{1}{2} C_{1} V_{1}^{2}-\frac{1}{2}\left(C_{1}+C_{2}\right) V_{c}^{2}$
$=6 \times 10^{-6} J$