Question

If a magnet is dropped through a vertical hollow copper tube, then?
A: The time taken to reach the ground is longer than the time taken if the tube was made out of plastic
B: The magnet will get attracted and stick to the copper tube
C: The time taken to reach the ground is longer than the time taken if the tube was made out of stainless steel
D-The time taken to reach the ground does not depend on the radius of the copper tube
E: the magnet will be repelled away by the tube.

Answer 1

Hint: A magnet produces a magnetic field around itself, the magnet has two poles- North pole and the south pole. The magnet field lines travel from the north pole to the south pole outside the magnet and from south pole to the north pole inside the magnet. Also, copper is metal and when the magnet moves near it magnetic flux will pass through it and since the magnet is moving so the associated flux will change.

Complete answer:
As soon as the magnet is dropped it approaches the copper tube, as it keeps on approaching the magnetic flux keeps on increasing until the magnet is fully inside the tube. From Faraday’s law of electromagnetic induction associated flux changes and so emf is induced and it is such that it opposes its cause of origin. So, it pushes the magnet upward, hindering its motion downward. This demonstrates that had the tube been of some non-metal then the time taken to reach the ground would have been less as compared to in this case.
So, the correct option is (A).

Note:
Faraday’s law of electromagnetic induction states a changing magnetic field induces potential difference inside a conductor placed in it. Faraday’s law states that a current will be induced in a conductor which is exposed to a changing magnetic field. Also, in the application of Faraday’s law, emf will be produced only if the flux changes and if there is no change in the flux, then there will be no induced emf.