In a bicycle speedometer, a bar magnet is attached to the spokes of the wheel and a

Question:

In a bicycle speedometer, a bar magnet is attached to the spokes of the wheel and a coil is attached to the frame so that the north pole of the magnet moves past it once for every revolution of the wheel. As the magnet moves past the coil, a pulse of current is induced in the coil. A computer then measures the time between pulses and computes the bicycle’s speed. The figure shows the magnet about to move past the coil. Which of the graphs shows the resulting current pulse? Take current counterclockwise in part (a) of the figure to be positive.