Force between two bar magnets.

[Mutaja]

Homework Statement

You're given two bar magnets as shown below. In the gap between the two bar magnets, there's a bit of copper that's 1mm thick. The area of the bar magnet is 2.5cm², and the flux density is 0.5T. Compute the force between the two bar magnets.

Homework Equations

The Attempt at a Solution

So the force is given by this formula:

F = B_∂ * H_∂ * A_∂

H_∂ = [itex]\frac{B_∂}{µ₀}[/itex] = $\frac{0.5T}{4∏ * 10^-7}$ = 397887

F = 0.5T * 397887 * $2.5cm^2$ = 497385.

The answer I get is about 20 000 times bigger than what I'm expecting.

Where am I going wrong?

F is the force.
B is the flux density in the air gap.
H is the field strength in the air gap.
A is the area in the air gap.

I'm sorry for the use of the wrong symbol, but ∂ was the closest I could get.

Also, I realized that I have a gap filled with copper instead of air, just as I was about to post this. I have no examples involving gaps with anything else than air as far as I'm aware. I will keep looking for this and update this post if I find anything.

Any input is appreciated.

 

[SteamKing]

Well, for one thing, you are sloppy and inconsistent with the units of your calculation. Is area supposed to be in cm^2 or m^2? It makes a difference.

 

[Mutaja]

Well, for one thing, you are sloppy and inconsistent with the units of your calculation. Is area supposed to be in cm^2 or m^2? It makes a difference.

I'm sorry for this. 2.5cm² should be 0.00025m².

Also, I've overlooked the fact that my equation should contain 1/2.

I therefore get 24.87N, and that looks alright.

Thanks for your input, even if it's just to let me know I'm not doing my work properly.