Question

A short cylindrical bar magnet is dropped down a vertical metallic pipe of slightly larger diameter, about 3 meters long. Estimate the falling time for the bar magnet to emerge at the bottom.

Answer 1

It will take a longer time than expected because as the magnet moves down the flux in the upper loop is decreasing and so the current in that loop is induced in the direction shown so that it will attract the north pole of the magnet, whereas the reverse is true for the downward loop as the flux through it is increasing in upward direction so it is pushing up the magnet ,so net force is decreased in downward direction so it will have an acceleration less than the value of gravity so it will reach the bottom at a time, T> seconds(taking acceleration due to gravity 10m/s² and applying displacement(s)=.5gt² where t is time in seconds and g is acceleration due to gravity) .N is north pole and S is south pole , I is the current induced in the loop.