Question

A bar magnet is pushed toward a loop of wire as shown in FIGURE Q30.7. Is there a current in the loop? If so, in which direction? If not, why not?

Short answer

As the bar magnet is pushed toward a loop of wire, the net magnetic flux through the loop is zero. Thus no current is induced in the loop.

Step-by-step solution

Given information

A bar magnet is pushed toward a loop of wire as shown in the figure below

Explanation

As the bar magnet is pushed toward a loop of wire, the net magnetic flux through the loop is zero, that is, all flux lines that enter the loop will, by symmetry, also exit the loop. Thus, no current is induced in the loop.

For this symmetry argument to hold, the magnet must be under the center of the loop.