A. A disk of radius R has an uneven surface load distribution: σ = C · r, where C is constant
and distance r is measured from the center O of the ring. Find a mathematical expression for the potential at a point P of the axis of the disk, which is a distance x from the center O.
Β. A compact sphere of radius R has a uniform load density distribution ρ and a total load Q. Find a mathematical expression that gives the total electrical energy of the sphere.