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Schfra

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## Homework Statement

Figure 6.47 shows a horizontal infinite straight wire with current I1 pointing into the page, passing a height z above a square horizontal loop with side length l and current I2. Two of the sides of the square are parallel to the wire. As with a circular ring, this square produces a magnetic field that points upward on its axis. The field fans out away from the axis. From the right-hand rule, you can show that the magnetic force on the straight wire points to the right. By Newton’s third law, the magnetic force on the square must therefore point to the left.

Your tasks: explain qualitatively, by drawing the fields and

forces, why the force on the square does indeed point to the left;

then show that the net force equals μ0I1I2l2/2πR2, where R =

z2 + (l/2)2 is the distance from the wire to the right and left sides of the square. (The calculation of the force on the wire is a bit more involved. We’ll save that for Exercise 11.20, after we’ve discussed magnetic dipoles.)

## Homework Equations

B = uI/(2piR)

## The Attempt at a Solution

I’m not quite sure where to start on this one. The first part of the question is a bit confusing, what do they want me to do? It seems like they already explained why the force on the square points left. Should I just draw a picture of what they already explained?

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