Why does the magnetic field/flux change in copper conductor?

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  • Thread starter CAH
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  • #1
CAH
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If you drop a permanent magnet like steel through a copper tube it induces an emf, this is because you have a change in magnetic field/flux? But how? Why? The copper isn't producing a current before the magnet is dropped into it... Does something happen with the electrons in the copper?
 

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  • #2
phyzguy
Science Advisor
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The electrons are present in the copper before you drop the magnet, but there is no emf, so they don't move. After you drop the magnet the changing B-field induces an emf in the copper, and the electrons move in response to the emf. The moving electrons are a current. Does this answer your question?
 
  • #3
CAH
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The electrons are present in the copper before you drop the magnet, but there is no emf, so they don't move. After you drop the magnet the changing B-field induces an emf in the copper, and the electrons move in response to the emf. The moving electrons are a current. Does this answer your question?
So do the electrons in the copper get attracted/repulsed by the magnet causing them to move? And when you say changing B field do you mean it goes from zero (in the copper) to experiancing the magnetic field of the steel? Yes I think so. Thank you
 
  • #4
Chandra Prayaga
Science Advisor
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You don't need a copper tube. A copper coil is enough. It is not that the electrons are attracted/repulsed by the magnetic field. In fact. If you hold the magnet and the coil still without moving either of them, there is no emf, even though there is a magnetic field. It is only when you drop the magnet, while the magnet is in motion, the flux through the coil changes, and the changing flux causes the emf.
 

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