Question

A short cylindrical bar magnet is dropped down a vertical aluminum pipe of slightly
larger diameter. The pipe is 1 m in length and the time to fall is measured from
the top of the pipe until the magnet fully emerges at the bottom. This “time of
fall” is compared to a similar (weight and size) piece of un-magnetized Fe and it is
found that the magnet goes much more slowly. Explain why this is and describe
the forces involved. What
will happen if you cut a slot along the length of this tube or if you change the tube
to copper.

Answer 1

By using Lenz's Law , as long as the magnet has a non zero acceleration, the flux linking with the aluminium tube will keep changing, and hence to opposes it a current and accompanying magnetic field will be induced that opposes that change in flux. This induced field will repel the the magnet in the direction opposite to its motion. Eventually the magnetic repulsion due to induced field by Lenz's Law will be equal to the gravitational pull on the magnet and it will reach a constant velocity.

When you drop your magnet through a copper tube, it slows down. The magnet will also slide down the cookie sheet slowly, and nudge the metal washer in the direction the magnet is spinning. The voltage will spike when the magnet is moving next to the metal, but not when the magnet is sitting still.