Question

A capacitor is charged to store an energy U. The charging battery is disconnected. An identical capacitor is now connected to the first capacitor in parallel. The energy in each of the capacitors is :

• A. 3 U/2
• B. U
• C. U/4
• D. U/2

Answer 1

The correct option is C U/4

Energy stored in a capacitor is $U=\frac{Q^2}{2C}$.
As the battery is disconnected, total charge $Q$ is shared equally by two capacitors.
So energy of each capacitor $=\frac{(Q/2{)}^2}{2C}=\frac{1}{4}\frac{Q^2}{2C}=\frac{U}{4}$.