The south pole of a bar magnet is moved toward a short helical coil of wire (solenoid) along the axis of the coil. The coil has 100 turns and the ends of the coil are connected to form a closed circuit. If the coil is replaced with a single loop of the same type of wire, and the magnet is moved exactly as before, the current induced in the loop is
A) the same as in the coil.
B) zero in both cases.
C) 100 times smaller.
D) 100 times larger.

Question

Quizplus · Accepted Answer

The induced current in a loop is proportional to the rate of change of magnetic flux through the loop. In the case of the coil with 100 turns, the change in flux through each turn adds up, effectively multiplying the induced emf (and thus the current, assuming resistance is constant) by the number of turns. When replaced with a single loop, the induced emf (and thus the current) would be 100 times smaller because the change in magnetic flux is only happening through one loop instead of 100.

The South Pole of a Bar Magnet Is Moved Toward