College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 30

In Figure P20.65 the rolling axle of length 1.50 m is pushed along horizontal rails at a constant speed v = 3.00 m/s. A resistor R = 0.400 is connected to the rails at points a and b , directly opposite each other. (The wheels make good electrical contact with the rails, so the axle, rails, and R form a closed-loop circuit. The only significant resistance in the circuit is R. ) A uniform magnetic field B = 0.800 T is directed vertically downward. (a) Find the induced current I in the resistor. (b) What horizontal force is required to keep the axle rolling at constant speed (c) Which end of the resistor, a or b , is at the higher electric potential (d) After the axle rolls past the resistor, does the current in R reverse direction Explain your answer.