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 \(=U_{i}-U_{f}=\frac{3}{8} C E^{2}\)