# Homework Help: Magnetic constant query

1. Jul 21, 2010

### winkZ

1. The problem statement, all variables and given/known data
Hi. I don't have any physics book at the moment. This has something to do with magnets&magnetic poles:

What is the force between two magnet poles of strengths 40amp-m and 50amp-m at a distance of 10cm in the air?

This sounds easy, but my problem is I don't know the magnetic constant to use. Our professor said the constant is 10^7N/Amp^2. But, I don't think its correct since he wasnt sure about it too. I tried to look for it in the net, but I can find nothing with that value...

Thanks

2. Relevant equations

Also, our professor told us that the formula is: F = (constant(q1)(q2))/(distance^2)

3. The attempt at a solution

so using the constant he gave us

F = (10^7N/A^2)(40amp-m)(50amp-m)/(0.10m)^2
F= 10^7(40)(50)N

Which seems correct, but i'm not sure about the value of the constant...

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

2. Relevant equations

3. The attempt at a solution

2. Jul 21, 2010

### Onamor

The constant he gave you is the http://en.wikipedia.org/wiki/Permeability_%28electromagnetism%29" [Broken].
Basically a measure of how "easily" a material (in this case vacuum) can support a magnetic field.

However it should be used in place of the Permittivity of free space you find in Coulomb's Law for electrostatics.

There appears to be a second (computational) mistake in your calculation as well.

Last edited by a moderator: May 4, 2017
3. Jul 21, 2010

### winkZ

thanks...a lot... i think i forgot the 0.01 :D thanks :D

Last edited by a moderator: May 4, 2017