In Figure P20.63, the rolling axle, 1.48 m long, is pushed along horizontal rail

Question

In Figure P20.63, the rolling axle, 1.48 m long, is pushed along horizontal rails at a constant speed s? = 6.00 m/s. A resistor R = 0396 ohm is connected to the rails at points a and b, directly opposite each other. (The wheels make good electrical contact with the rails, and so the axle, rails, aid R form a closed-loop circuit. The only significant resistance in the circuit is R.) There is a uniform magnetic field B = 0.0700 T vertically downward. (a) Find the induced current I in the resistor. (b) What horizontal force F is required to keep the axle rolling at constant speed? N (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? Yes No

Explanation / Answer

(a)induced current=induced emf / resistance

induced emf =magnetic field x axle length xspeed

induced current=0.07 x 1.2 x 6 / 0.396 =1.27 ampere
(b)force=magnetic field x current x length of axle=0.07x1.27x1.48=0.132 newton

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