$\frac{d v}{d y}=\frac{\sigma}{K \epsilon_{o}}$
$\int_{0}^{v} d v=\frac{\sigma}{\lambda \epsilon_{o}} \int_{0}^{d} \cos \left(\frac{\pi y}{2 d}\right) d y V$
$=\frac{\sigma}{\lambda \epsilon_{o}} \times \frac{2 d}{\pi}\left[\sin \frac{\pi y}{2 d}\right]_{0}^{d}$
$=\frac{\sigma}{\lambda \epsilon_{o}} \times \frac{2 d}{\pi}$
$C=\frac{Q}{V}=\frac{A \lambda \epsilon_{o} \pi}{2 d}$

