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...

A) larger.

B) the same.

C) smaller.

D) indeterminate.

Solution: C. The capacitance decreases as the plates are separated since distance is in the denominator of the formula for capacitance of a parallel plate capacitor. The potential difference remains the same because the plates remain connected to the battery. Using the formula U = 1/2*C*(ΔV)^2, the energy decreases.