How is EMF Induced in a Moving Straight Wire in a Constant Magnetic Field?

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Discussion Overview

The discussion centers on the phenomenon of electromotive force (emf) induced in a straight conducting wire moving at a constant velocity within a constant magnetic field. Participants explore the relationship between motion, magnetic fields, and induced emf, referencing Faraday's law and contrasting different scenarios involving stationary and moving wires.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that Faraday's law emphasizes the need for changing flux to induce emf in stationary wires, questioning how emf can be induced in a moving wire.
  • Another participant agrees that while a stationary wire requires changing flux, a moving wire can also induce emf, suggesting that motion through a magnetic field plays a crucial role.
  • Several participants express confusion about the difference between a moving straight wire and a loop of wire, with one asserting that a loop moving through a constant magnetic field does not induce emf due to lack of flux change.
  • A suggestion is made to visualize the situation with a drawing to clarify the concepts, emphasizing that a loop must change its orientation relative to the magnetic field to induce emf.
  • One participant mentions that producing a change in electric potential can drive charges around a closed circuit, linking this to the concept of induced emf.
  • Another participant argues that there is no fundamental difference between a moving straight wire and a loop, except that current can flow in the coil, which may complicate the discussion.
  • It is proposed that even if the magnetic flux is not changing, the motion of the wire causes the magnetic field to be 'swept through,' affecting the charge carriers within the wire.
  • A participant introduces the term "motional emf" to describe the emf induced by the motion of the wire through the magnetic field.

Areas of Agreement / Disagreement

Participants express differing views on the conditions necessary for emf induction, particularly regarding the role of changing flux and the comparison between straight wires and loops. The discussion remains unresolved with multiple competing perspectives on the topic.

Contextual Notes

Some assumptions about the nature of magnetic fields and the behavior of charge carriers in different configurations are not fully explored. The discussion also reflects varying interpretations of Faraday's law and its applications to different scenarios.

fletch-j
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We just went over Faraday's law in class and our teacher stressed how a changing flux is needed to induce an emf in some coil/loop/wire.
I was just wondering then, how is an emf induced in a straight conducting wire moving at a constant velocity in a constant magnetic field? It seems as if Δϕ=0...
I think ε=vBl is the equation which is used to describe this phenomena.
 
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yes. Your teacher meant that for a stationary wire, a changing flux is required to create an emf. But if the wire is moving through a magnetic field, then an emf can also be created, as you said.
 
But if you have a loop of wire moving through a constant magnetic field then there is no change in flux so no induced emf.. What is the difference between a moving straight wire and a loop/coil?
 
fletch-j said:
But if you have a loop of wire moving through a constant magnetic field then there is no change in flux so no induced emf.. What is the difference between a moving straight wire and a loop/coil?

I suggest you draw a picture & you can see things better. A pic always helps. If the loop is normal to the flux continuously & flux is uniform, there is no induction. But if the loop spins so that the angle w/ the flux changes, then induction takes place.

A good book on motors/generators will illustrate this better than I can verbally describe things. My advice to all pondering such questions is to - draw a picture. Drawing a picture really makes things easier to understand. That is why I always like to draw a picture. It beats words by a big margin.

Draw a picture. BR.

Claude
 
prior posts all look ok...

Any way you can produce a change in electric potential will push charges around a closed circuit.
Some explanatory viewpoints here:

http://en.wikipedia.org/wiki/Induced_emf
 
fletch-j said:
But if you have a loop of wire moving through a constant magnetic field then there is no change in flux so no induced emf.. What is the difference between a moving straight wire and a loop/coil?

There is no difference between the loop and straight wire (except that a current can flow in the coil, causing secondary effects, but we don't need to make this more complicated by thinking about them).

As I said before, if the wire is stationary, then there must be a change in flux to create an emf, but this is not true if the wire is moving.

Think about the charge carriers moving through the wire. If the wire is moving (in addition to them moving along the wire), then there is an extra velocity which the charge carriers must have. And so the magnetic field will have an extra effect on the charge carriers due to the fact that the wire is moving.

Or another way to think about it is that although the flux is not changing, the magnetic field is being 'swept through', as the wire moves through it. P.S. this kind of emf is called motional emf (which makes sense really).
 

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