How to Calculate Energy and Force in an Air Gap of an Inductor?

[madmike159]

Homework Statement

There is a pic of a L shaped coil (2 L's facing each other but one is upside down).
Air gap = 1 mm
Turns = 200
current = 2A
perm of material = 4000 (relative)

I have found the reluctance by drawing a magenitic circuit diagram and i got 41003 which I've been told was right.

Now I need to find the energy in the air gap and the force between the two peices.

Homework Equations

B = \muNI/L
where \mu is the permibility
B is flux density
N is number of turns
I is current
and L is length of the path

How ever I think this is for a toroid.

E = B^2/\mu(L*A)
Where E is energy
B is flux density
\mu is permibility (of the section (air))
L and A are the dimentions of the section

F = B^2 * A / 2*\mu

The Attempt at a Solution

I get 5x10^9 J for energy and about 8KN for force.

I think I'm going wrong workingo ut B because I get 0.502T

 

[cragar]

So do you basically have a square solenoid?

 

[madmike159]

Yes, but I have managed to solve it now.