When a magnetic field changes and an emf is produced,

AI Thread Summary
The discussion centers on the phenomenon of electromagnetic induction when a magnet is dropped through a copper tube, raising questions about the source of energy for the induced electromotive force (emf). It is clarified that the energy comes from the gravitational potential energy of the magnet, which is converted into kinetic energy and subsequently into electrical energy as the magnet induces a counterclockwise current in the copper. The participants also explore how the magnet's speed affects the induced current, noting that a slower drop results in more energy being converted into emf. Additionally, spinning the magnet is mentioned as a method to stabilize its fall, which may influence the current induced. Overall, the conversation emphasizes the relationship between gravitational energy, kinetic energy, and induced emf in this context.
jaredvert
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Then what gives the energy to create this emf?
 
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What makes the magnetic field change from top to bottom of the tube if we drop a magnet in a copper tube?
 
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nsaspook said:
What makes the magnetic field change from top to bottom of the tube if we drop a magnet in a copper tube?
It is the induced emf in the copper tube correct? It would make a counterclockwise current. But what I don't understand is where is the energy for this induced emf coming from?
 
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jaredvert said:
Yeah I mean I think I get lenz law but can u explain what I'm missing here? The magnet falling induced a counterclowise current in the copper. Where the energy for this emf is what I don't understand

What makes the magnet move?
 
nsaspook said:
What makes the magnet move?
Well gravity but I imagine it's acceleration is slower due to the magnetic force exerted on it
 
nsaspook said:
Yes, the person uses energy to pick up the magnet to some height from it's rest position and then release it to fall in the tube due to gravity.

http://www.physicsclassroom.com/class/energy/Lesson-1/Potential-Energy
Oh so I see because it has less velocity it's KE is less and so the energy induced to the emf is equal to mgh - 1/2mvf^2. Where vf is velocity in coil. Correct?
 
  • #10
Judging by the slow speed of the magnet drop in the tube a good percentage of the KE is in the induced emf and it's magnetic field.
 
  • #11
nsaspook said:
Judging by the slow speed of the magnet drop in the tube a good percentage of the KE is in the induced emf and it's magnetic field.
How come when he spins it the magnet accelerates faster down? Is it because the area of the plates perpendicular to the sides are smaller and so smaller current induced?
 
  • #12
jaredvert said:
How come when he spins it the magnet accelerates faster down? Is it because the area of the plates perpendicular to the sides are smaller and so smaller current induced?

At what point in the video do you mean? His spin is mainly to stabilize the magnet during it's drop.
 

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