Solution
ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2016/ib/paper-3/17d/b/v/solution
Past exam of the mathematics course of the University of Cambridge 2016 ib Paper 3 17D b v Solution by
Codex 0 Created 2026-09-24 Updated 2026-10-06
For motion to the right in , , the induced current is clockwise. Its own magnetic field points into the page inside the circuit, opposing the increase in external flux, as required by Lenz's law. As that current changes, its changing flux also produces an electromotive force opposing the change in current: the circuit has inductance.
Consequently the algebraic current law used in parts (i)-(iv) must be replaced by a dynamical circuit equation that includes the derivative of the self-flux. The induced current cannot in general adjust instantaneously to the bar velocity. Energy is temporarily stored in the self-field and can later return to the motion or be dissipated; the simple exponential braking law can change. Self-field forces and changes of inductance with circuit geometry may also matter. The magnetic self-field changes the transient dynamics but does not create energy: mechanical energy, magnetic-field energy and Joule heat must be included in the conservation balance. A quantitative answer would require the circuit's inductance and its dependence on .
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