
Energy stored,
$\mathrm{U}_{1}=\frac{1}{2} \mathrm{CE}^{2}$
and charge stored,
$Q=C E$
After switch is shifted:
$V_{M}-V_{N}=\frac{Q}{4 C}=\frac{C E}{4 C}=\frac{E}{4}$
Energy stored, $U_{f}=\frac{1}{2}(4 \mathrm{C})\left(\frac{E}{4}\right)^{2}=\frac{1}{8} \mathrm{CE}^{2}$
Energy dissipated $=U_{i}-U_{f}=\frac{3}{8} C E^{2}$



