A dielectric sphere of radius a and permittivity ɛ is situated in vacuum and charged through its density by a volume charge density of free charges p = Po, R being the distance from the center of the sphere. Determine, a) Electrostatic energy of the system, b) Change in the electrostatic energy of the system if a point charge, Q, is added to the system at the center of the sphere.

A dielectric sphere of radius a and permittivity ɛ is situated in vacuum and charged through its density by a volume charge density of free charges p = Po, R being the distance from the center of the sphere. Determine, a) Electrostatic energy of the system, b) Change in the electrostatic energy of the system if a point charge, Q, is added to the system at the center of the sphere.