12. A capacitor is to be constructed so that its capacitance is 0.2µF and to take a p.d. of 1.25kV across its terminals. The dielectric is to be mica which, after allowing a safety factor of 2, has a dielectric strength of 50MV/m. Find (a) the thickness of the mica needed, and (b) the area of a plate assuming a two-plate construction.