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
As we learnt in
Energy Stored -
The potential energy of a charged capacitor
where is the initial potential energy. If a dielectric slab is slowly introduced, the energy
Once is taken out, again the energy increases to the old value. Therefore after it is taken out, the potential energy come back to the old value.
Total work done =ZERO