# Magnetism Strenght

Discussion in 'Electronic Basics' started by Camilo Andres Gil Cardona, Aug 17, 2003.

1. ### Camilo Andres Gil CardonaGuest

Hi everybody! i need to know which is the equation for calculate the
atraction or repulsion strenght of a magnetic field from a natural
magnet or a coil, preferably the coil(repulsion when equal poles are
confronted)... other thing, ¿Does increase the magnetic atraction when
two opposite poles are confroted that when a single pole (of a magnet
or coil) atracts a ferromagnetic material?! beforehand, thanks for any

2. ### Charles SchulerGuest

To get started go to http://152.66.73.137/research/field/mam.html

3. ### John PopelishGuest

In the most general terms, the force produced by any magnetic circuit
depends on how much the total flux varies with the motion of the parts
in question. If the flux changes more per unit of motion, the force
is higher. Since the is no limit ot the geometric choices you have,
there can be no simple mathematical rule to predict the force. The
whole flux path and all its geometry has to be modeled.

4. ### Harry ConoverGuest

Excellent answer John, but for the laymen here lets complicate things
just a bit as a simple puzzle.

For the purposes of the puzzle, let's assume that we have a large "C"
shaped magnet with a 3/4" spacing between its pole faces.

The questions:

1. (easy) I we hold a 1/4" thick plate of mild iron midway between the
ple faces, when we release it will it be attracted to the N pole or
the S pole of the magnet? In other words, in which direction is the
magnetic attraction?

2. (requires a bit more thought) Assuming again that we hold the iron
plate midway between the pole pieces, the magnetic flux path is though
the magnet itself, then though a 1/4" airgap, through the iron plate,
though another 1/4" air gap and then back into the body of the magnet
itself. Why would the net flux be different when the iron plate is
attracted to and in contact with one of the magnet's pole pieces,
since the reluctance of the magnetic path appears to be the same in
both cases? (The magnetic flux has to change for magnetic attraction
to take place.)

I suppose you could call these brain teasers, but I do know of at

Have fun.

Harry C.

5. ### John PopelishGuest

Good one. But what is the shape of the 1/4" thick plate? Knowing the
phase of the moon might help too. ;-)
Why would you assume the reluctance is the same in both cases, unless
you assumed the flux lines are parallel between the pole pieces, and
this condition is unaffected by the presence of the iron plate.

But that would be a silly pair of assumptions.