Energy in capacitors: An ideal air-filled parallel-plate capacitor has round plates and carries a fixed amount of equal but opposite charge on its plates. All the geometric parameters of the capacitor (plate diameter and plate separation) are now DOUBLED. If the original capacitance was C₀, what is the new capacitance?

Question

Quizplus · Accepted Answer

The capacitance of a parallel-plate capacitor is directly proportional to the plate area and inversely proportional to the plate separation. Doubling the diameter of the plates will quadruple the plate area (since area of a circle is proportional to the square of its diameter), and doubling the plate separation will halve it. Therefore, the new capacitance will be (4C)/(2) = 2C, where C is the original capacitance. Thus, the answer is B.

Energy in Capacitors: an Ideal Air-Filled Parallel-Plate Capacitor Has Round