why magnets attract or repel each other

by hushai1
Tags: magnet, magnetic force, magnetic work
hushai1 is offline
Nov17-11, 02:26 AM
P: 7
I would like to understand at a microscopic level why magnets attract or repel each other. I understand that there are tiny loops of currents caused by the spin and orbital rotations of electrons, that there are magnetic moments, but I don't understand why magnets attract. How is the magnetic force (F=qv x B) acting? What is doing the work since magnetic forces are not doing any work? Thank you
Phys.Org News Partner Physics news on Phys.org
Physicists consider implications of recent revelations about the universe's first light
Vacuum ultraviolet lamp of the future created in Japan
Grasp of SQUIDs dynamics facilitates eavesdropping
Bill_K is online now
Nov17-11, 01:46 PM
Sci Advisor
Bill_K's Avatar
P: 3,856
Consider one of the magnets (1) to be a tiny current loop, and ask how it will be influenced by the magnetic field of the other magnet (2). The force on each moving charge in the current loop is e v x B. At opposite sides of the loop the v's are equal and opposite, so in a uniform B field the force averages out to zero.

But near the pole of magnet 2 the B field is not uniform. Near the North pole the lines of B will be diverging, while near the South pole they will be converging. That means the circular loop does not just see a B field perpendicular to its plane, it also sees an additional radial component to the B field pointing outward (or inward). Since v is tangential and B is radial, v x B will be perpendicular to the plane of the loop, and the loop will be attracted (or repelled).
hushai1 is offline
Nov17-11, 06:35 PM
P: 7
Thank you for your answer. I think it is a good answer. I don't understand however, why, if magnetic forces don't work, there is still some work done since one magnet is able to attract another magnet. Thank you.

Register to reply

Related Discussions
Do Electrons Attract AND Repel? General Physics 10
magnets attract and oppose, right? Mechanical Engineering 2
How can magnets repel paperclips? General Physics 1
[SOLVED] Can an electrostatic force repel or just attract? General Physics 15
Do magnets attract objects in a straight line? Classical Physics 0