Consider a thin metal sphere of radius b and has charge Q. 

What is the capacitance? 

b) What is the energy density of the electric field at a distance r from the sphere centre? 

c) What is the total energy of the field? 

d) Compute the work expended in charging the sphere by carrying infinitesimal charges from infinity 

e) A potential V is established between inner (radius a) and outer (radius b) concentric