Why do eddy currents cause oscillations to die away quickly?

In summary, the oscillation of a metallic disc attached to a rod between two magnetic poles dies away quickly due to both the resistive force caused by eddy currents and the heating effect of these currents. Both explanations are correct and do not contradict each other. The direction of the eddy currents is determined by Lenz law, and the dissipation of energy through heat is a result of the turbulent motion caused by the currents.
  • #1
PFuser1232
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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?
 
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  • #2
Both explanations are correct.
 
  • #3
dauto said:
Both explanations are correct.

Could you please elaborate further?
 
  • #4
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.
 
  • #5
dauto said:
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?
 
  • #6
MohammedRady97 said:
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.
 
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  • #7
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.
 

1. What are eddy currents?

Eddy currents are circular currents induced in a conductor when it is exposed to a changing magnetic field.

2. How are eddy currents related to Lenz's Law?

Lenz's Law states that the direction of an induced current will oppose the change that caused it. In the case of eddy currents, they are induced in a way that creates a magnetic field that opposes the original changing magnetic field.

3. What factors affect the strength of eddy currents?

The strength of eddy currents is affected by the strength and rate of change of the magnetic field, the electrical conductivity and size of the conductor, and the geometry of the conductor.

4. How are eddy currents utilized in technology?

Eddy currents are used in various technologies, such as induction heating, electromagnetic brakes, and metal detectors. They can also cause unwanted energy loss and heating in electrical devices.

5. Can eddy currents be controlled or minimized?

Yes, eddy currents can be controlled or minimized by using materials with low electrical conductivity, laminating conductors, and shaping conductors to reduce their surface area. These techniques are commonly used in electrical transformers and motors to reduce energy loss.

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