Consider a metallic pipe with an inner radius of 1 cm. If a cylindrical bar magnet of radius 0.8cm is dropped through the pipe, it takes more time to come down than it takes for a similar un-magnetized cylindrical iron bar dropped through the metallic pipe.

In this case, eddy current will produce due to induction, actually when a cylindrical bar magnet of radius 0.8 cm is dropped inside a hollow cylindrical metallic pipe of radius 1 cm, the magnetic flux across the pipe changes. As we know magnetic flux is so it’s depend on area as well.

Now the direction of eddy current in this case will be in accordance with Lenz’s law i.e. it can oppose the cause, in this case cause is the motion of magnet. So upward force acts on bar magnet and decreases the acceleration, due to deceleration it takes more time to fall magnet through the pipe, as compared to similar un-magnetized cylindrical iron bar.


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