A capacitor consists of two stationary plates shaped as a semi-circle of radius `R` and a movable plate made of dielectric with permittivity `K` and capable ofrotating about an axis `O` between the stationary plates. The thickness of movable plate is equal to `d` which is practically the separation between the stationary plates. A potential difference `V` is applied to the capacitor. Find the magnitude of the moment of forces relative to the axis `O` acting on the movable plate in the position shown in figure.