EMF induced in conducting wire

In summary, our teacher explained that a changing flux is needed to induce an emf in a stationary wire, but if the wire is moving through a magnetic field, an emf can also be created due to the motion of charge carriers. This can be better understood by drawing a picture and considering the extra velocity of the charge carriers due to the motion of the wire. This type of emf is known as motional emf and is important to understand in motors and generators.
  • #1
fletch-j
19
0
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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  • #2
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.
 
  • #3
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?
 
  • #4
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
 
  • #5
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
 
  • #6
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).
 

1. How is EMF induced in a conducting wire?

When a conducting wire is placed in a changing magnetic field, an EMF (electromotive force) is induced in the wire. This occurs due to the interaction between the moving magnetic field and the free electrons in the wire, which causes the electrons to move and create an electric current.

2. What factors affect the magnitude of the induced EMF?

The magnitude of the induced EMF depends on the strength of the magnetic field, the rate at which the magnetic field is changing, and the length and orientation of the wire in relation to the magnetic field.

3. How does the direction of the induced EMF relate to the direction of the magnetic field?

The direction of the induced EMF is perpendicular to both the direction of the magnetic field and the direction of motion of the wire. This is known as Faraday's Law of Induction.

4. What is the difference between EMF induced in a conducting wire and EMF generated by a battery?

The EMF induced in a conducting wire is a result of a changing magnetic field, while the EMF generated by a battery is a result of chemical reactions. Additionally, the induced EMF is temporary and only exists while the magnetic field is changing, while the EMF from a battery is constant.

5. How is the induced EMF used in practical applications?

The induced EMF can be used in various applications, including generators, electric motors, and transformers. It is also used in technologies such as wireless charging and electromagnetic induction cooktops.

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