150CHAPTER 19 19.19For the wire to move upward at constant speed, the net force acting on it must be zero. Thus, sinBILmgθ=and for minimum field 90=°. The minimum field is ( )( )()( )20.015 kg9.80 m s0.5.0 A0.15 mmgBIL===20 T For the magnetic force to be directed upward when the current is toward the left, Bmust be directed out of the page . 19.20The magnitude of the magnetic force exerted on a current-carrying conductor in a magnetic field is given by sinFBI=l, where Bis the magnitude of the field, is the length of the conductor, Iis the current in the conductor, and lis the angle the conductor makes with the direction of the field. In this case, ( )( )( ) ( )0.390 T5.0n5.46 N sin
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