PHYSICS · Multi-part · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
A rectangular copper frame of mass 150g, resistance 0.10Ω, width 0.20m (horizontal dimension) and length 0.30m (vertical dimension) is released from rest and allowed to fall vertically into a region of uniform vertical magnetic field of 0.40T directed downward. Outside this region the magnetic field is negligible. Neglect air resistance.
(i) While the lower edge of the frame is entering the field, state the direction of the induced current as seen from above and give reason.
(ii) Derive an expression for the upward magnetic force acting on the frame in terms of its instantaneous speed v while it is partly inside the field.
(iii) Show that the frame attains a constant terminal speed and obtain an expression for this terminal speed in terms of the given parameters and g.
(iv) Calculate the numerical value of the terminal speed using g=9.8ms−2.