What do capacitors oppose?

What do capacitors oppose?

• A. A change in current
• B. A change in voltage
• C. Heat
• D. Frequency

Answer: (B)

Capacitors oppose changes in the voltage across them. The current through a capacitor follows i = C dv/dt, so it responds to how fast the voltage is changing. If the voltage across the capacitor tries to jump suddenly, dv/dt is large and the capacitor must supply or absorb a large current to prevent that instantaneous voltage change. That’s why, after an initial transient, a DC voltage across an ideal capacitor becomes steady and the current goes to zero—the voltage change is no longer happening. Heat isn’t the capacitor’s main function, and while the impedance of a capacitor depends on frequency (Z = 1/(jωC)), that relation reflects how the circuit responds to changing voltages rather than the capacitor opposing frequency itself.

Capacitors oppose changes in the voltage across them. The current through a capacitor follows i = C dv/dt, so it responds to how fast the voltage is changing. If the voltage across the capacitor tries to jump suddenly, dv/dt is large and the capacitor must supply or absorb a large current to prevent that instantaneous voltage change. That’s why, after an initial transient, a DC voltage across an ideal capacitor becomes steady and the current goes to zero—the voltage change is no longer happening. Heat isn’t the capacitor’s main function, and while the impedance of a capacitor depends on frequency (Z = 1/(jωC)), that relation reflects how the circuit responds to changing voltages rather than the capacitor opposing frequency itself.