What is the purpose of a capacitor?

• A. Stores energy in magnetic fields.
• B. Stores electrical energy in electrostatic fields.
• C. Converts AC to DC.
• D. Dissipates energy as heat.

Answer: (B)

Capacitors store energy in the electric field created between two plates separated by a dielectric. When voltage is applied, charges accumulate on the plates, forming an electrostatic field that holds energy. The amount of energy stored is 1/2 C V^2, where C is the capacitance and V is the voltage across the plates. This ability to hold and release energy quickly makes capacitors useful for smoothing power supply ripple, coupling signals between stages, and timing circuits.

This energy storage is electric, not magnetic, which is why inductors store energy in magnetic fields around a coil. A device that converts AC to DC is a rectifier, and a resistor dissipates energy as heat.