Question

A common physics demonstration is to drop a small magnet down a long, vertical aluminum pipe. Describe the motion of the magnet through the pipe and explain the physical processes that cause this motion.

Answer 1

Answer and Explanation:

This experiment is known as Lenz's tube.

The Lenz tube is an experiment that shows how you can brake a magnetic dipole that goes down a tube that conducts electric current. The magnet, when falling, along with its magnetic field, will generate variations in the magnetic field flux within the tube. These variations create an emf induced according to Faraday's Law:

$\varepsilon =-\frac{d\phi_B}{dt}$

This emf induced on the surface of the tube generates a current within it according to Ohm's Law:

$V=IR$

This emf and current oppose the flux change, therefore a field will be produced in such a direction that the magnet is repelled from below and is attracted from above. The magnitude of the flux at the bottom of the magnet increases from the point of view of the tube, and at the top it decreases. Therefore, two "magnets" are generated under and above the dipole, which repel it below and attract above. Finally, the dipole feels a force in the opposite direction to the direction of fall, therefore it falls with less speed.

Answer 2

Answer:

Check below for the answer and explanation

Explanation:

According to Faraday's law of electromagnetic induction, if a conductor is exposed to changing magnetic flux, an emf and hence a current is induced in the conductor. The strength of the induced emf is directly proportional to the rate of change of the magnetic flux.

Induced emf, $e =-N\frac{d \phi}{dt}$

Induced current, I = e/R

In this example, as magnet is dropped down the aluminium pipe, the magnetic flux changes, and current is induced in the pipe.

According to Lenz's law, the direction of the induced current in the conductor opposes the direction of the magnetic flux that produces it.

Based on these stated laws, current is induced in this aluminium pipe and the direction of this induced current opposes the magnetic flux change. The magnetic field is repelled and falls slowly.