A conducting rod is allowed to slide down a pair of vertical
PHYSICS · Subjective · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A conducting rod is allowed to slide down a pair of vertical, frictionless conducting rails that are connected at their lower ends by a resistance R. A uniform magnetic field is directed horizontally and perpendicular to the plane of the rails.
(i) Using Lenz’s law, explain why an induced current appears in the circuit and state its direction.
(ii) Describe qualitatively how the motion of the rod is affected by the induced current. Why does the rod attain a constant speed instead of accelerating indefinitely under gravity?
(iii) Explain, without detailed calculation, how energy conservation is maintained in this situation, identifying the forms in which energy is transformed.