Q. A parallel plate condenser with a dielectric constant between the plates has a capacity and is charged to a potential 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

 3466  225 Electrostatic Potential and Capacitance Report Error

Solution:

Energy stored in parallel plate capacitor of Capacitance and Potential is

When the dielectric slab is removed from, between the capacitor energy stored

is the capacitance in the presence of dielectric
is the capacitance in the absence of dielectric
and we have where is the dielectric constant
When the dielectric slab is reinserted the potential energy becomes
U =
Hence the net work done in the process is zero