A circular wire loop rests in a uniform magnetic field that is oriented perpendicular…
PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A circular wire loop rests in a uniform magnetic field that is oriented perpendicular to the plane of the loop and directed into the page. At the instant a stopwatch is started, a student begins to pull equally on all sides of the loop so that its radius increases smoothly from 4.0 cm to 6.0 cm in 2.0 s while the field magnitude remains constant.
Throughout this process you observe the loop from the side on which the magnetic field points into the page.
(a) Qualitatively describe how the magnetic flux through the loop changes during the 2.0 s interval.
(b) Indicate the direction (clockwise or counter-clockwise, as viewed by you) of the induced current in the loop while it is expanding.
(c) Explain your answer to part (b) in terms of the underlying physical principle that governs the relationship between a changing magnetic flux and the induced current.
(d) The loop’s resistance is 0.25 Ω. Without performing explicit numerical calculations, discuss whether doubling the rate at which the radius expands would increase, decrease, or leave unchanged the magnitude of the induced current at any given radius. Justify your reasoning.