A parallel plate condenser with a dielectric of dielectric constant K between the plates has a capacity C and is charged to a potential V volt. The dielectric slab is slowly removed from between the plates and then reinserted. The net work done by the system in this process is
(a) zero
(b) 1/2(K - 1)CV2
(c) CV2(K - 1)/K
(d) (K - 1)CV2
