Question

A popular demonstration of eddy currents involves dropping a magnet down a long metal tube and a long glass or plastic tube. As the magnet falls through a tube, there is changing flux as the magnet falls toward or tube of an other side

Answer 1

Eddy currents are produced when a magnet falls through a conducting material because as magnet falls the changing magnetic flux opposes the motion of the magnet and the magnet takes a little more time to travel through the tube.

Metal tubes are conducting so eddy currents will be produced in it.

Glass and plastic tubes are insulator means non conducting so there will not be eddy currents through the tube.

So, eddy currents will be only produced in metal tubes not in glass and plastic tubes.