Drivability Practice Exam

Self-induced voltage comes from a changing magnetic flux in a coil. When current in a coil changes, the magnetic field it produces changes as well, and Faraday’s law says that a voltage is induced to oppose that change (Lenz’s law). If the current is being reduced, the magnetic field collapses and the flux through the coil changes rapidly. The coil then generates a voltage that tries to keep the current flowing, which is the self-induced voltage. This is why the scenario described—collapsing magnetic fields due to a reduction of current—best matches how self-induced voltage works. The other options don’t describe a changing flux (constant field), or describe the external source situation rather than the coil’s own response, and while increasing current also involves an opposing emf, the typical textbook description highlights the collapsing field from decreasing current.