Electromagnetic induction question

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Discussion Overview

The discussion revolves around calculating the force acting on a conductor moving through a magnetic field, specifically in the context of electromagnetic braking systems for trains. Participants explore the relationship between current, magnetic fields, and the resulting forces, as well as the implications of using permanent versus electromagnets.

Discussion Character

  • Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant asks how to calculate the force on a conductor in a magnetic field, relating it to electromagnetic braking.
  • Another participant provides the formula for force, indicating the roles of current, conductor length, and the magnetic field.
  • A participant inquires about the differences in calculations when using a permanent magnet instead of an electromagnet.
  • It is suggested that the origin of the magnetic field (permanent or electromagnet) does not affect the formula used for force calculation.
  • There is a question about whether a current is necessary in the conductor for force to be present, leading to clarification that a current is indeed required for force generation.
  • A participant notes that in magnetic braking, the current is induced by varying magnetic flux, emphasizing the role of the electromagnet.

Areas of Agreement / Disagreement

Participants appear to agree on the necessity of current in the conductor for force generation, but there is some ambiguity regarding the implications of using different types of magnets and whether the formula remains unchanged in those scenarios.

Contextual Notes

The discussion does not resolve the specific conditions under which the force calculations apply, nor does it clarify the assumptions regarding the magnetic field's source or the nature of the induced current.

Who May Find This Useful

Individuals interested in electromagnetic systems, particularly in applications related to braking mechanisms in trains or similar technologies.

bill nye scienceguy!
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How do I calculate the force (in Newtons) acting on a conductor moving through a magnetic field? This is in relation to an electromagnetic brake by the way; I need to work out the deceleration of train as it moves through the braking zone.

Thanks.
 
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Force is [tex]\vec F=I\ell \vec u\times\vec B[/tex]
Here [tex]\vec u[/tex] is a vector parallel to the current and pointing in the same direction.
[tex]I[/tex] and [tex]\ell[/tex] are the current and the conductor length.
 
Thanks! As an aside, how would you work it out if you use a permanent magnet rather than an electromagnet?
 
The origin of B doesn't matter, it can be generated by an electromagnet as well as by a permanent magnet.
 
so the equation remains the same? does that mean there has to be a current in the conductor rather than in the magnet?
 
Yes. No current, no force.
In a magnetic brake the current in induced by the varying magnetic flux.
Only electromagnets need current to generate the magnetic field.
 
Thanks for all that, I wish I'd had this discussion 2 months ago - would have made a project much easier.
 

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