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Hiro · Sep 19, 2008, 01:52 PM

I need to know how large of an electromagnet I need to make in order to push a second electromagnet with a certain amount of force. Is there an equation which relates Teslas to Force and distance?

ebaines · Sep 22, 2008, 12:03 PM

Trying to calculate the attraction force between magnets is very complex, because it is highly dependent upon the magnets' geometries and distribiution of magnetic poles. The force between two magnetic poles is:

$F =\frac { \mu q_ {m1} q _{m2}} {4 \i r^2}<br />$

where:
$F$ is force in Newtons, $q_{m1}$ and $q_{m2}$ are magnitudes of magnetic poles (in ampere meter), $\mu$ is the permiability of the medium in tesla-meter/ampere, and $r$ is the separation in meters. In real world applications the pole distribution is more complex than a simple north and south poles, so a more complex form is often required. For two bar magnets, for example, the force between them can be found from:

$<br /> F = \left[ \frac {B_0 ^2 A^2 (L^2 + R^2)} {\pi \mu _0 L^2} \right ] \left [ \frac 1 {x^2} + \frac 1 {(x + 2L)^2} - \frac 2 {(x+L)^2} \right ]<br />$

where $B_0$ is the magnetic flux density near the poles in tesla, $A$ is the area of each pole, $L$ is the length of each magnet, $R$ is the radius of each magnet, and $x$ is the separation of the two magnets.

See also:
Magnet - Wikipedia, the free encyclopedia

Hiro · Sep 23, 2008, 05:53 AM

Thank you so, so much for helping me with this. What I need to calculate the forces of is a bit more complicated however;

I need to calculate with how much force a solonoid will push a bar magnet if it has, say, its north pole inside the north end of the solonoid and the south pole outside.

Think a track running through the center of the solonoid with the magnet positioned in the way I have described. I have a feeling that this is going to be much harder to calculate then I had first imagined heh.

ebaines · Sep 23, 2008, 05:59 AM

Yes - quite complicated. You may be able to find some software that can help with the calculation, using finite elements. Or if you have one of these solenoids handy perhaps you can do an experiment using different weights.