A capacitor is connected to a 12-volt power supply by a reed switch operating at 400 Hz.  The ammeter reads 45 mA.  What is the capacitance of the capacitor?

C = 0.045 A ¸ (400 Hz × 12.0 V) (P)

C = 9.38 × 10^-6 F = 9.38 mF (P)