Register to reply

Eddy Currents and Lenz's Law

by MohammedRady97
Tags: currents, eddy, lenz
Share this thread:
MohammedRady97
#1
May17-14, 11:39 AM
MohammedRady97's Avatar
P: 99
A metallic disc attached to a rod swings between two opposite magnetic poles, and its oscillation dies away very quickly. I thought this happens because the eddy currents formed inside the disc are established in a direction that would cause their magnetic field to oppose the magnetic field which induced them, causing a resistive force on the disc, just like air resistance but much stronger. And since the amplitude is a measure of the total mechanical energy of the disc, and work is done against the "resistive forces", the amplitude decreases. However, my A level book says otherwise. According to my book, eddy currents cause a heating effect which dissipates energy in the disc causing the oscillations to die away. Thoughts on this please?
Phys.Org News Partner Physics news on Phys.org
Scientists uncover clues to role of magnetism in iron-based superconductors
Researchers find first direct evidence of 'spin symmetry' in atoms
X-ray laser probes tiny quantum tornadoes in superfluid droplets
dauto
#2
May17-14, 11:49 AM
Thanks
P: 1,948
Both explanations are correct.
MohammedRady97
#3
May17-14, 12:02 PM
MohammedRady97's Avatar
P: 99
Quote Quote by dauto View Post
Both explanations are correct.
Could you please elaborate further?

dauto
#4
May17-14, 12:10 PM
Thanks
P: 1,948
Eddy Currents and Lenz's Law

Both things you said are correct. The induced currents produce a magnetic field that opposes the preexisting field forcing the pendulum to slowdown. The energy of the pendulum is dissipated which means it is transformed into heat. That heat is deposited in the metallic disk because the eddy currents have a heating effect. Both things are true. One explanation does not preclude the other explanation. They are both correct.
MohammedRady97
#5
May17-14, 12:11 PM
MohammedRady97's Avatar
P: 99
Quote Quote by dauto View Post
Both things you said are correct. The induced currents produce a magnetic field the oppose the preexisting field forcing the pendulum to slowdown. The energy of the pendulum is dissipated which means it is transformed into heat. That heat is deposited in the metallic disk because the eddy currents have a heating effect. Both things are true. One explanation does not preclude the other explanation. They are both correct.
But a heating effect would be caused by the current anyway, regardless of its direction, right?
dauto
#6
May17-14, 12:14 PM
Thanks
P: 1,948
Quote Quote by MohammedRady97 View Post
But a heating effect would be caused by the current anyway, regardless of its direction, right?
Yes, but only one direction works. Lenz law gives you the correct direction.
dauto
#7
May17-14, 12:17 PM
Thanks
P: 1,948
May be an analogy will help. If you shoot a bullet into a water tank the water will slow down the bullet. You can say that the drag produces a force that slows down the bullet but you can also say that turbulent motion converts the energy of the bullet into heat. Both the force and the energy points of view are correct.


Register to reply

Related Discussions
Eddy currents General Physics 3
Eddy currents Classical Physics 3
Foucault currents / Eddy Currents vs material selection Engineering, Comp Sci, & Technology Homework 0
Eddy currents General Physics 1
Eddy currents General Physics 0