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Electrostatic Potential and Capacitance

Question

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. Find the net work done by the system in this process.

Answer

While charging the capacitor, a certain amount of work is done on the system. And, when the dielectric is removed, an equal amount of work is done by the system. Since, the work done on the system and work done by the system is equal, net amount of work done is zero.