A capacitor consists of two metal plates separated by an insulator, as shown in the figure below.
The potential difference between the plates is 
. The variation with of the magnitude of the charge 
on one plate is shown in the graph below.
Explain why the capacitor stores energy but not charge.
Use the graph above to determine
the capacitance of the capacitor,
the loss in energy stored in the capacitor when the potential difference is reduced from 
to 
.
.
