Which statement best describes a capacitor's voltage behavior under load?

Which statement best describes a capacitor's voltage behavior under load?

• A. It can maintain a constant voltage indefinitely.
• B. It increases voltage over time after energy input stops.
• C. It always rises with time.
• D. It cannot maintain voltage; voltage changes as it discharges.

Answer: (D)

The voltage on a capacitor under load changes because it stores a finite amount of charge for a given capacitance. Since Q = C V, the voltage is determined by how much charge is stored. When a load draws current, charge leaves the capacitor, so dQ/dt is negative and the voltage drops: dV/dt = (1/C) dQ/dt = -I/C. If the current is roughly constant, the voltage falls roughly linearly over time. Only with a replenishing source would the voltage stay constant; otherwise the capacitor simply discharges and its voltage decreases. In real life, leakage also causes a slow drop even with no load, but the key idea is that under load the capacitor cannot maintain a steady voltage—it discharges.

The voltage on a capacitor under load changes because it stores a finite amount of charge for a given capacitance. Since Q = C V, the voltage is determined by how much charge is stored. When a load draws current, charge leaves the capacitor, so dQ/dt is negative and the voltage drops: dV/dt = (1/C) dQ/dt = -I/C. If the current is roughly constant, the voltage falls roughly linearly over time. Only with a replenishing source would the voltage stay constant; otherwise the capacitor simply discharges and its voltage decreases. In real life, leakage also causes a slow drop even with no load, but the key idea is that under load the capacitor cannot maintain a steady voltage—it discharges.