What is the basic function of a capacitor?

• A. Induces voltage
• B. Produces magnetic field
• C. Blocks DC
• D. Stores energy temporarily and blocks DC while allowing AC depending on frequency

Answer: (D)

A capacitor stores energy in the electric field between two plates separated by an insulating material. When you apply a voltage, charge collects on the plates and energy is stored briefly in that field. In a direct-current situation, once the capacitor charges, no steady current flows, so it effectively blocks DC. With alternating current, the voltage keeps changing, so the capacitor continuously charges and discharges, allowing current to flow. The amount of AC current that gets through depends on frequency: the impedance is 1/(2πfC), so higher frequencies face lower impedance and pass more easily, while low frequencies (including DC) are blocked more strongly. This combination—storing energy temporarily and blocking DC while permitting AC to pass (depending on frequency)—is the basic function of a capacitor.