When a magnetic field changes and an emf is produced,

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Discussion Overview

The discussion revolves around the phenomenon of electromagnetic induction, specifically focusing on the energy source for the induced electromotive force (emf) when a magnet falls through a copper tube. Participants explore the mechanics of the magnetic field changes, the resulting currents, and the implications of Lenz's Law.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question what provides the energy for the induced emf when a magnet falls through a copper tube.
  • There is a repeated inquiry about the nature of the magnetic field change and its relationship to the induced emf and the resulting counterclockwise current.
  • One participant suggests that the energy for the induced emf comes from the gravitational potential energy of the magnet, which is converted as it falls.
  • Concerns are raised about the effect of the magnetic force on the magnet's acceleration as it falls, with some suggesting that the induced emf affects its kinetic energy.
  • Participants discuss the relationship between the speed of the magnet and the induced currents, with questions about how spinning the magnet influences its acceleration.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the source of energy for the induced emf and the mechanics of the magnet's motion. Multiple competing views remain about the interactions between gravitational energy, kinetic energy, and induced emf.

Contextual Notes

There are unresolved questions about the mathematical relationships between potential energy, kinetic energy, and induced emf, as well as the specific conditions affecting the magnet's motion in the tube.

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?
 
Last edited by a moderator:
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?
 
Last edited by a moderator:
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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