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Homework Statement
A ring falls through a horseshoe magnet. Before reaching the magnet, is the current induced in the ring clockwise or counterclockwise? What about after the ring has passed through the magnet?
The answers are clockwise before the ring passes through, and counterclockwise after. I'd like to understand why this is so.
Homework Equations
Lenz' law, a magnetic field will be induced on the ring to oppose change in magnetic flux in the magnetic field of the magnet.
The Attempt at a Solution
Part A) Before reaching the magnet
When falling, the magnetic flux is increasing because more magnetic field lines of the magnet pass through the ring. By Lenz' law, a magnetic field will be induced on the ring to resist this, so the magnetic force would push it upwards, and the direction of the magnetic field would be opposite to the direction of the magnetic field of the horseshoe magnet.
Using the right-hand rule, I have B from right to left (Lenz' law), F upwards. Thus, v at the bottom of the ring would be going right, which is counterclockwise, which is incorrect.
Part B)
The ring is moving away, decreasing the flux, so by Lenz' law, a magnetic field is induced on the ring where the force is upwards. Since the field is attempting to maintain itself here, the induced magnetic field points in the same direction as the magnet's field. B is from left to right, F is upwards, so v at the top of the ring is going left, which is counterclockwise, which is correct.
How should I do part A? Is my explanation for part B correct? I don't know if my usage of the right-hand rule is correct, since it applies to particles and I'm for the direction of current ring, and current flowing right/left at any point in a ring is flowing in the opposite clock direction of at the opposite side of the ring.