I have two identical magnets, each with dimensions of 10mm x 10mm x 2mm and weighing 20 grams. I drill a very small hole through each magnet so they can ride up and down (frictionless) on a small pole.

Now if I position one magnet on the ground, north pole facing up, and the other magnet on the pole with north pole facing down, the magnets will repel each other.

The question is, what is the formula I need to use to work out the field strength required to keep them 10mm apart.

H=(0.4 pi NI)/l

H = magnetizing force (oersteds)
N = no. of turns
I = peak current (amperes)
l = magnetic path (cm)


this is the only magnetic formula i can remember? :p