When a magnetic field changes and an emf is produced,

  1. Then what gives the energy to create this emf?
     
  2. jcsd
  3. nsaspook

    nsaspook 1,137
    Science Advisor

    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: Sep 25, 2014

  4. 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: Sep 25, 2014
  5. UltrafastPED

    UltrafastPED 1,918
    Science Advisor
    Gold Member

  6. nsaspook

    nsaspook 1,137
    Science Advisor

    What makes the magnet move?
     

  7. Well gravity but I imagine it's acceleration is slower due to the magnetic force exerted on it
     
  8. nsaspook

    nsaspook 1,137
    Science Advisor


  9. 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. nsaspook

    nsaspook 1,137
    Science Advisor

    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. 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. nsaspook

    nsaspook 1,137
    Science Advisor

    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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