# How do I calculate the repelling Force of an Electromagnet?

1. Jun 26, 2015

### jason Kenedy

Hello everyone, I am working on a project and I am trying to figure out the formula to use. My goal is to calculate the amount of current needed to create an electromagnet with a strong enough field strength to repel a force of 2000 newtons.
thank you

2. Jun 26, 2015

### Hesch

The short answer is: 400000 A/m.
But of course it depends on:

* What kind of magnet ( shape ).
* Dimensions of the magnet and the other magnet to be repelled. ( for example unmagnetized iron will always be attracted ).

So you need to fill out "All known data:".

Last edited: Jun 26, 2015
3. Jun 26, 2015

### jason Kenedy

Thanks. Actually I just found this formula. I can reverse solve for m1 and m2 which is the pole strength of each electromagnet I would be using for the project. and then solve for the current I need.

4. Jun 26, 2015

### Hesch

I don't recognize this formula. What is m1 and m2: Masses, or?

Say you have two magnets kept apart with a distance, s. The cross section areas of the magnets are A. The energy density within the airgap will be

Edens = ½*B*H [ J/m3 ] ( = ½*μ0*B2 )

The energy in the airgap will be E = ½*B*H*Volumeairgap = ½*B*H*s*A

Now, you can find the force: F = dE/ds = ½*B*H*A.

But what is the size of A?