# Magnetic Forces on objects in nonuniform fields

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1. Jun 22, 2017

### Astronaut

• Moved from a technical forum, so homework template missing.
I have this question which I need to solve . But I am unable to.

Suppose I have a current ring of radius R and current I (constant).

at a distance x from the centre of the ring, I have a iron disk (radius r and thickness t) present in the plane of the ring. This disk will be attracted to the ring due to magnetisation.

How do I calculate the force it experiences due to the field? Should I use F = ∇(m · B)??

I just want a way to solve it not the complete solution.. Any help is appreciated.

2. Jun 22, 2017

### haruspex

Not sure what set up this describes. I would expect it to be that the iron disk is parallel to the plane of the ring, and coaxial with the ring. You seem to be saying it is coplanar with the ring with the two centres distance x apart, but if so I am not sure what it means to say the disk is attracted "to the ring".

3. Jun 23, 2017

### Astronaut

Yes the disk is coplanar to the ring. I read that in non uniform fields, magnetic forces are acted on a magnetic dipole. Won't the same happen here?

4. Jun 23, 2017

### haruspex

I'm sure there will be forces, but I do not know what "to" the ring means here. If it moves towards one part of the ring it is moving away from another part. Do you mean towards the centre of the ring?