Chapter 20, Problem 65AP

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 resist or R = 0.400 Ω 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 $\stackrel{\to }{F}$ 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) Alter the axle rolls past the resistor, does the current in R reverse direction? Explain your answer.

Figure P20.65