[A-Level Physics] Magnetic & Electric Fields Experiment (Help!) Watch

FP5
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Hello,

This is in Module 6 - OCR A Level Physics

I have seen this experiment where a magnet is put through a metal tube, but moves really slowly through the tube.

Why is this? What's going on?
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FP5
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- bump -
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Jackudy3
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Magnets?

*shudders*, just had a flashback to the AQA AS Physics exam on Friday.
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Ladkus
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There are two ways of looking at it. One using conservation of energy and the other using lenz's law. When the magnet falls through the tube, there is a changing magnet field as the magnet passes through the tube. Using Faraday's law of induction, this change in flux linkage causes a current to be induced in the tube. If you were to look at conservation of energy, before you release the magnet, it will have gravitational potential energy, and after the magnet has fallen through it will have kinetic energy. However, some of the potential energy has been dissipated as heat inside the tube due to the induced current. If you were to look at it with Lenz's law, then the direction of the induced current would be such that it opposes the change that caused it. This would mean the direction of the current induced will create a magnetic field that opposes the magnetic field of the magnet, which would repel the magnet hence apply an upwards force, causing the magnets acceleration to decrease as the resultant force on the magnet is much less.
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