1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why magnets attract or repel each other

  1. Nov 17, 2011 #1
    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
  2. jcsd
  3. Nov 17, 2011 #2


    User Avatar
    Science Advisor

    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).
  4. Nov 17, 2011 #3
    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.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook