Induced voltage occurs under which condition?

• A. When current is constant
• B. When current is changing
• C. When resistance is zero
• D. When voltage is zero

Answer: (B)

Induced voltage comes from a changing magnetic flux through a circuit. In most everyday cases, that changing flux happens when the current in a nearby conductor or coil changes, since the magnetic field around a wire is proportional to the current. When the current changes, the magnetic flux linked with a loop changes, and Faraday’s law says an emf is generated in response to that changing flux. If the current is constant, the flux is not changing, so no induced voltage appears.

The other conditions don’t inherently produce changing flux: having zero resistance isn’t by itself a trigger for induction, and having zero voltage doesn’t cause the flux to change. The key idea is that a time-varying current causes a time-varying magnetic flux, which induces voltage.