–

Say the north pole of the magnet is facing the ring. Note that the magnetic flux of the magnet is captured by the aluminum ring.

When the magnet is lifted away from the ring, the magnetic flux density at the ring decreases. An emf is induced around the ring since the ring experiences a change in flux linkage (Faraday’s Law, ε=-dΦ/dt). The direction of the induced emf (and current) should be such as to produce an effect to oppose the change that resulted in the induced emf in the first place (Lenz’s Law). Since the ring experiences a decreasing downward magnetic flux, the direction of induced current must be to produce a downward magnetic flux as well (in an attempt to arrest the decreasing magnetic flux). Since the magnetic field of the magnet and the ring are in the same direction, the ring experiences an attractive magnetic force that lifted the ring off the table.

• Uncategorized