kbar1

Suppose a (parallel plate) capacitor of capacitance C is charged to a potential difference V and then disconnected and isolated. Energy stored E₁= Q²/2C.

Now if a material of appropriate dimensions and dielectric constant K is fully inserted between the plates, energy stored E₂= Q²/2KC.

E₂ < E₁.

My question is: where did the "missing" energy go?