A Long Vertical Wire Carries a Steady 70 a Current

Multiple Choice

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-Ω 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? (μ₀ = 4π × 10^-7 T ∙ m/A)

A) 0.63 μA, from a to b
B) 0.63 μA, from b to a
C) 0.32 μA, from a to b
D) 0.32 μA, from b to a
E) 1.9 μA, from b to a