(1) A copper bar of length L = 1.0 m is sliding along two silver rails separated
ID: 1837011 • Letter: #
Question
(1) A copper bar of length L = 1.0 m is sliding along two silver rails separated by 0.5 m. The bar is sliding at speed v = 2.0 m/s through a uniform magnetic field B = 3.0 T everywhere directed out of the plane. The rails have negligible electric resistance and, surprisingly, the resistance of the contacts is negligible. The resistance of the bar is Rbar 0.020 over the full length of the bar. The rails may be connected through an external resistance Rm = 0.0100 by closing switch . (a) Find the potential difference Vab between the rails if the switch is open. df 2 ext (b) Find the potential difference Vab between the rails if the switch is closed. (c) Find the potential difference Vef between the ends of the bar if the switch is open.Explanation / Answer
a) If the switch is open then the voltage is rate of change of flux = B*L/2*v = 3*0.5*2=3V
b) If the switch is closed then the current =3/(0.01+0.02)=100A ,so voltage = 0.02*100=2V
c) if the switch is open then voltage = BLv = 6V
d)if the switch is closed voltage is 2+B*L/4*v+B*L/4*v=3+2=5V
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