A rectangular conducting loop moves with constant velocity completely inside a region…
PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A rectangular conducting loop moves with constant velocity completely inside a region where a uniform magnetic field is directed out of the page and perpendicular to the plane of the loop. Which statement best explains why the magnitude of the induced emf in the loop is zero while the loop is entirely inside the field region?
(a) The charges in the loop experience no magnetic force because the loop’s velocity is parallel to the magnetic field.
(b) The induced current quickly grows until it cancels the external field everywhere inside the loop, so no net emf remains.
(c) The magnetic flux through the loop remains constant, since neither the field strength nor the loop’s area changes while it is inside the region.
(d) An emf is produced only while the loop crosses the edge of the field region; once it is fully inside, the loop is effectively at rest with respect to the field, so the emf drops to zero.