Capacitors & Capacitance Practice Test

A capacitor stores energy in an electric field between two plates separated by an insulator (the dielectric). Its capacitance, measured in farads (F), depends on plate area, plate spacing, and the dielectric material. In a DC circuit, a fully charged capacitor blocks current — it acts like an open circuit. In an AC circuit, a capacitor continually charges and discharges as the voltage reverses, so current keeps flowing; its opposition to that current is called capacitive reactance (X_C = 1 / (2πfC)), which goes DOWN as frequency goes UP. Never forget: a large capacitor can hold a dangerous charge even after power is removed.