Please help, why does polarity of a magnet switch when going through a coil?

Hi, could you please write exactly what happens and why when a magnet slowly falls through an electric coil.....thanks!

The magnet induces a current in the coil, which itself produces a magnetic field. This magnetic field opposes the field of the magnet so the magnet is repelled. This is why if it is falling, it slows down


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Thank you but why does emf become negative as the magnetic is leaving the coil according to a emf vs time graph?

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If the current and voltage is in one direction as it enters, it will go in the other direction as it leaves.

If the magnet is out, the coil doesn't want it in, so current travels in the direction that causes the magnet to be repelled. But once the magnet is in, the coil doesn't want it to leave, so the current flips around to attract the magnet back in

The current in a solenoid is always such that the resulting magnetic field opposes that which caused the current.

If a magnet goes in North side first, then the coil will have North at the point where it is entering (the top) to repel it. When the magnet is leaving, the coil will have North at the bottom to attract it.

(Hope that makes sense )


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Ah yes this answer is what I've been looking for! Thank you! But in an exam would I be allowed to say the coil doesn't want the magnet to leave? Or should I say that the polarity of the coil switched and this is because.....


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Hi, could you please write exactly what happens and why when a magnet slowly falls through an electric coil.....thanks!

It's Lenz's Law:




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Yes thank you!! could you please show where figure 2 is aswell please... Thanks

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Yes thank you!! could you please show where figure 2 is aswell please... Thanks

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Thank you!!

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If the current and voltage is in one direction as it enters, it will go in the other direction as it leaves.

If the magnet is out, the coil doesn't want it in, so current travels in the direction that causes the magnet to be repelled. But once the magnet is in, the coil doesn't want it to leave, so the current flips around to attract the magnet back in

The current in a solenoid is always such that the resulting magnetic field opposes that which caused the current.

If a magnet goes in North side first, then the coil will have North at the point where it is entering (the top) to repel it. When the magnet is leaving, the coil will have North at the bottom to attract it.

(Hope that makes sense )


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It's Lenz's Law:




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I believe a lot of students have learnt that "Lenz's law is the result of conservation of energy" but I would like to propose a different view.


This is a discussion among physics teachers in a physics forum and I find that it is an interesting discussion and has some interesting answers, so I share it here.

If your exam board is stating that you need to explain Lenz's law through conservation of energy, don't propose another view.

A lot of physics textbooks explain Lenz's law saying that law of conservation of energy would be violated if Lenz's law is not applied. I find that the analysis is usually incomplete because the magnetic field is NOT taken into account. I personally believe if a complete analysis that include the electromagnetic field, energy would be conserved. Just my two cents of opinions.