Question

the energy store in a capacitor is 4J. the charge on it is double without changing the p.d the energy stored is ​

Answer 1

Let initial charge on the capacitor was Q and capacitance is C

The energy stored in the capacitor is given as:

E=2CQ2

21CQ2=4 J

As the new capacitor is connected, the net charge will be distributed between the capacitors.

Now, when two capacitors of same capacitance are present:

⇒E′=214CQ2+214CQ2

⇒E′=212CQ2

⇒E′=2 J