A capacitor consists of two concentric metallic spheres with radius Ra and Rc where Ra < Rc. The inner sphere carries a charge Q and the outer sphere carries a charge ‐Q. (a) If the spheres are separated by vacuum, find the capacitance. . (b) If the in between the shells (between Ra and Rc), two types of materials are filled with different dielectric constants 1and 2. The radius of boundary is given by Rb. Find the corresponding capacitance.