How does an inductor respond to a sudden change in current?

• A. It stores energy in a magnetic field
• B. It becomes a short circuit
• C. It resists the change by inducing a voltage opposing the change
• D. It stops current flow

Answer: (C)

An inductor responds to a sudden change in current by generating a voltage that opposes that change. When the current through a coil changes, the magnetic field around it changing induces an emf in the windings that acts to oppose the change in current (Lenz's law). The induced voltage is proportional to how quickly the current is changing (V = L di/dt). So if the current tries to rise quickly, the induced voltage acts opposite to the applied current and slows the rise; if the current tries to fall, the inductor’s voltage tries to keep current flowing. This behavior is also why an inductor stores energy in its magnetic field. It does not automatically become a short circuit or stop current by itself.