When a magnetic field changes and an emf is produced,

[jaredvert]

Then what gives the energy to create this emf?

 

[nsaspook]

What makes the magnetic field change from top to bottom of the tube if we drop a magnet in a copper tube?

 

[jaredvert]

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?

 

[UltrafastPED]

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?

See Lenz's Law: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

 

[jaredvert]

See Lenz's Law: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

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

 

[nsaspook]

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?

 

[jaredvert]

What makes the magnet move?

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

 

[nsaspook]

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

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

 

[jaredvert]

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?

 

[nsaspook]

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.

 

[jaredvert]

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?

 

[nsaspook]

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.