A hollow sphere of radius 2R is charged to V volts and another smaller sphere of radius R is charged to volt V/2 . Then the smaller is placed inside the bigger spher without changing the net charge on each sphere. the petential differenbce between the 2 spheres would be

a) 3V/2   b) V/4   c) V/2   d) V

 i have answered here

http://iit-redefined.zzl.org/viewtopic.php?f=7&t=481&p=2716#p2716

potential of outer spher is V+V/4(V/4 is due to the internal sphere on outer sphere) potential of inner sphere is V+V/2(V due to outer on inner) .

so the diff. is V/4(b)