Consider a simple parallel-plate capacitor whose plates are given equal and are separated by a distance d. The plates are connected to opposite terminals of a battery. The plates remain connected to the battery while being pulled apart by a scientist with insulating gloves until they are separated by a distance D>d. The electric energy stored in the capacitor is now smaller. Where did the energy go?

A) the battery

B) the scientist

C) North Dakota

D) indeterminate

Solution: A. Since the capacitance decreases and the electric potential difference remains the same, the definition of capacitance (C = Q/Δ V) indicates that the charge decreased. So the capacitor discharged through the battery. Either the battery got hotter (increased its thermal energy) or "recharged" (increased its chemical energy), depending upon its design.