2) A long vertical wire carries a steady 70 A current. As shown in the figure, a

Question

2) A long vertical wire carries a steady 70 A current. As shown in the figure, a pair of horizontal rails are 0.20 m apart. A 20- resistor connects points a and b, at the end of the rails. A bar is in contact with the rails, and is moved by an external force with a constant horizontal velocity of 0.90 m/s to the right, as shown. The bar and the rails have negligible resistance. At the instant that the bar is 0.20 m from the wire, what are the induced current in the resistor and its direction through the resistor? (0 = 4 × 10-7 T·m/A) +0.20 m v= 0.90 m/s 70 A 20 0.20 m

Explanation / Answer

The equation for magneitc field due to long straight wire is

B= uo I/ 2pi d

= 4 pi * 10^-7 ( 70)/ 2pi (0.20) = 7* 10^-5 T

formula for current is

I = e/R = BLv/ R = 7* 10^-5 ( 0.2) (0.9)/20 = 0.6 * 10^-6 A

direction is from a to b ( clock wise direction)

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