Aresistor r = 0.450 ω is connected to the rails at points a and b, directly opposite each other. the wheels make good electrical contact with the rails, and so the axle, rails, and r form a closed-loop circuit. the only significant resistance in the circuit is r. there is a uniform magnetic field b = 8.10×10-2 t vertically downward. calculate the induced current i in the resistor.