Question

If an isolated capacitor loses energy when a dielectric is introduced, where does that energy go?

• A. The plates of the capacitor do work to move the dielectric between the plates.
• B. The energy drains out when charges are lost from the capacitor plates.
• C. The energy is taken by the current flow through the dielectric
• D. Capacitor is a special case where conservation of energy does not apply.

Answer 1

The correct option is A The plates of the capacitor do work to move the dielectric between the plates.

If you try to insert a dielectric inside a charged isolated capacitor , you’d feel the capacitor pulling it. This is because on the surfaces of the dielectric opposite charge gets induced and they attract each other. The capacitor “does work” on pulling the dielectric in. Now doing work needs what? energy!
so the overall energy decreases!
It’s an isolated capacitor so charge can’t go anywhere and hence the charge separation is maintained. And current flowing through a dielectric makes no sense! It’s an insulator.
AND THE MOST IMPORTANT POINT conservation of energy is a law which is never violated in universe as far as we know about the universe by now i.e. 2016.