The gap between the plates of a plane parallel plate capacitor is filled with an isotopic insulator whose dielectric varies in direction perpendicular to the plates according to law  $K=[1+\sin \left(\frac{\pi x}{d}\right)]$ where d is separation between plates and A is area of each plate. If capacitance of the capacitor is  $\left(\frac{\lambda A{\in }_0}{d}\right)$ then find the value of   $\lambda$