Answer:
U0/2
Explanation:
The potential energy stored by a capacitor is given by:
(1)
where
C is the capacitance
V is the potential difference applied across the capacitor
The capacitance of the parallel plate capacitor, at the beginning, is given by
where is the permittivity of free space, A is the area of the plates, and d is the separation between the plates. Substituting this into eq.(1), we can write the initial potential energy stored in the capacitor as
Later, the separation between the plates is doubled:
while the potential difference is kept constant. Therefore, we can calculate the new potential energy:
So, we see that the potential energy has been halved.