# Current-carrying Wire in a Circular Magnet

1. Aug 4, 2012

### LovePhys

1. The problem statement, all variables and given/known data

Determine the direction of the force acting on the current-carrying wire in the magnetic field.

2. Relevant equations
Lenz's Law

3. The attempt at a solution
This problem confuses me as the current is moving in a circular loop. However, I tried to use Lenz's Law and got the right answer: The direction of the magnetic force is out of the page, but I do not know whether I did the right thing or not.

I used the right hand rule: I put my thumb on the loop in the direction of the current (this is where I am confused since the current moves in the circular loop, not in a straight conductor as I normally do in class). Then my fingers point in the direction of the magnetic field lines. As a result my palm points in the direction of the force, which is out of the page.

Thank you very much for all your help!
LovePhys
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

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2. Aug 4, 2012

### Simon Bridge

Repeat your usual rule for lots of points on the wire - treat the current and all as being straight just for that point. See if it makes any difference where you use the rule for.

I use the left-hand finger rule myself but the RH-slap is good too.

3. Aug 5, 2012

### LovePhys

Thank you very much Simon Bridge!

I understand what you mean! It really does not make any difference! I tried treating the loop as many tiny straight current-carrying conductors and it worked! :)

4. Aug 5, 2012

### Simon Bridge

No worries - this method (treating as many small straight bits) works for most things and the exceptions are usually pretty obvious. Basically if it looks flat when you zoom in - like with a circle - it'll work.