Which property opposes changes in voltage?

• A. Inductors
• B. Capacitors
• C. Resistance
• D. Impedance

Answer: (B)

Capacitors resist rapid changes in voltage because their voltage is tied to the amount of charge stored on their plates. The current through a capacitor is i = C dv/dt, so the rate at which the voltage can change (dv/dt) depends on the current you can push through it. To make the voltage jump quickly, you’d need a large current, which isn’t available instantaneously in practice; thus the voltage across a capacitor cannot change abruptly. That tendency to smooth out voltage fluctuations is why capacitors are often used to stabilize power supplies and to couple signals while blocking DC.

Inductors behave differently: they resist changes in current, not voltage. Their defining relation v = L di/dt means a changing current induces a voltage that opposes that change. Resistance, described by V = IR, limits current but doesn’t specifically oppose how fast voltage changes; it’s about how much current flows for a given voltage. Impedance describes the total opposition to AC, combining resistance and reactance, and isn’t a single property that targets voltage changes the way a capacitor’s behavior does.