198CHAPTER 20 (b) The induced current through the axle will cause the magnetic field to exert a retarding force of magnitude rFBI=Avon the axle. The direction of this force will be opposite to that of the velocity Gso as to oppose the motion of the axle. If the axle is to continue moving at constant speed, an applied force in the direction of vGand having magnitude apprF=()Fmust be exerted on the axle. ())(0.800 A10.8 NappFBI===A0 T9.01.50 m(c) Using the right-hand rule, observe that positive charges within the moving axle experience a magnetic force toward the rail containing point b, and negative charges experience a force directed toward the rail containing point a. Thus, the rail containing bwill be positive relative to the other rail. Point is then at a higher potential than ba, and the current goes from
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