# Eddy Current Pendulum

1. Sep 8, 2008

### ElectroJ

I am trying to understand how the Eddy current pendulum works. I know that the changing magnetic field will generate the eddy currents in the pendulum due to Faraday's Law, and that these currents will align so as to oppose the magnetic field. But where does the force come from? If its due to Lorentz force on the circulating eddy currents shouldn't the force on one side of the loop be equal and opposite to the other side and hence cancel each other out?

2. Sep 8, 2008

### cesiumfrog

Is it because the field is stronger on one side of the loop?

3. Aug 31, 2009

### ajclegg

My understanding is that it's not the Lorentz force that creates the drag force, but rather the North-South attraction (and/or like pole repulsion) of the permanent magnet and the field induced by the eddy currents. Lenz's Law states (as you point out), that the eddy currents will be induced in a direction such that they will create a field opposing the original external field - as such, if you imagine the induced field as a virtual bar magnet, the north will be near south of the external, and vice versa.

As far as the Lorentz forces acting on the electrons in the conductor, I am a little stuck here, because it seems like the Lorentz force would act radially inward, "trying to shrink" the diameter of the current loop. This doesn't make sense to me, so I'm stuck on that point. I agree that they all should cancel, however, and thus not contribute to the drag force.

-Aaron.