Two conducting spherical shells have charges q and −q respectively. The inner shell has a radius a and the outer shell has a radius b. What is the capacitance (C) of the system of two shells?
a) C= 4πϵₒab / b+a
b) C= 4πϵₒab / b-a
c) C= 4πϵₒa²b² / b-a
d) C= 4πϵₒa²b² / b+a
