Swinging a hanging copper ring with a bar magnet

[versine]

Homework Statement

Figure 34-26 shows a copper ring that is hung from a ceiling by two threads. Describe in detail how you might most effectively use a bar magnet to get this ring to swing back and forth.

Relevant Equations

Faraday's law
Force on current carrying wire

I thought of few scenarios and they ended up as follows:
The ring must have an induced current. Due to the symmetry of the ring, if one part of the ring feels a force, the part of the ring radially opposite this part will feel a force opposite in direction, since the current will be opposite in direction relative to the magnetic field. So they will either cancel out or cause the ring to spin, even if the magnetic field is moved to one side, making one side stronger.

 

[Delta2]

No, the ring will not spin, in my opinion it will move back and forth (that is in direction normal to the plane of the page) as long as the magnet is moving along the normal direction too and of course inside the area of the ring.

 

[versine]

No, the ring will not spin, in my opinion it will move back and forth (that is in direction normal to the plane of the page) as long as the magnet is moving along the normal direction too and of course inside the area of the ring.

In that case won't everything cancel?

 

[Delta2]

In that case won't everything cancel?
View attachment 286533

The magnetic field from a bar magnet isn't exactly as you put it in that picture. It has a component like this (a z- component) but it also has x and y components (xy is the plane of the page). It is the force due to the x and y components that will make the current loop swing back and forth.

 

[versine]

Thanks, makes sense

 

[berkeman]

I wonder if you get a better swinging motion of the ring if you move the bar magnet left to right and back across the face of it, or if you push the magnet in and out of the ring in the direction normal to the page...

 

[Keith_McClary]

All I could find is a piece of copper plumbing and a hard drive magnet.