Chapter 30: Q. 2 (page 868)

You want to insert a loop of copper wire between the two permanent magnets in FIGURE Q30.2. Is there an attractive magnetic force that tends to pull the loop in, like a magnet pulls on a paper clip? Or do you need to push the loop in against a repulsive force? Explain

Short Answer

Expert verified

Initially, there is no magnetic flux through the loop. When the loop is positioned between the poles of the magnet, magnetic flux will pass through the loop.

According to Lenz’s Law, the current flows in the direction required to oppose a change in flux, so the current will flow in the direction required to create a repulsive force on the copper wire.

The current induced in the loop is therefore in the direction shown, that is, into the page on the left side of the copper loop.

Step by step solution

Given information

A loop of copper wire between the two permanent magnets is shown in the figure below

Explanation

In its initial position, there is no magnetic flux through the loop.

When the loop is positioned between the poles of the magnet, magnetic flux will pass through the loop.

According to Lenz’s Law, the current flows in the direction required to oppose a change in flux, so the current will flow in the direction required to create a repulsive force on the copper wire.

The current induced in the loop is therefore in the direction shown, that is, into the page on the left side of the copper loop.

The magnetic poles of the induced current loop are also shown in the diagram. The resulting magnetic force on the loop is to the right.

The above description is shown in the figure below