if a dielectric slab of dielectric constant K is introduced between the plates of a parallel plate capacitor completely , how does the energy density of the capacitor change?

For a normal parallel plate capacitor the energy density is given as

u = (1/2)ε0E2


for a capacitor filled with dielectric the energy density is given as

u' = (1/2)εE2


ε = Kε0

K - dielectric constant


u' = (1/2)Kε0E2

thus, we get

u' = Ku

so, change in energy density will be

du = u' - u = Ku - u


du = u.(K-1)

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