# Why does a changing magnetic field induce a current?Watch

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Thread starter 5 years ago
#1
I've seen this demonstration done in class, but never heard an explanation of why it actually works.

I know that electricity and magnetism are both parts of the same force, but that in itself doesn't provide enough of an explanation of this.

Thanks for helping.

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5 years ago
#2
(Original post by majmuh24)
I've seen this demonstration done in class, but never heard an explanation of why it actually works.
(...)
Do you know the flow density? it consists of the magnetic field lines of the magnetic field. The closer the magnetic field lines the stronger the magnetic field. The magnetic field gets weaker the other way round. So the change of magnetic field is based on 'strecthing' or 'concentrating' the magnetic field lines. If this change happens in a conductor, so a current is induced by electromagnetism.
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5 years ago
#3
God.
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Thread starter 5 years ago
#4
(Original post by Kallisto)
Do you know the flow density? it consists of the magnetic field lines of the magnetic field. The closer the magnetic field lines the stronger the magnetic field. The magnetic field gets weaker the other way round. So the change of magnetic field is based on 'strecthing' or 'concentrating' the magnetic field lines. If this change happens in a conductor, so a current is induced by electromagnetism.
I haven't heard this concept before, but that's probably because I'm at GCSE level right now. It makes sense that a magnet is stronger when the field lines are closer, but what I'm asking is WHY concentrating the magnetic field lines causes a current to be induced.

Does it have some effect on the electrons in a conductor that cause a charge to flow?

(Original post by TurboCretin)
God.
I was looking for a more physics based answer, but sure.

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5 years ago
#5
(Original post by majmuh24)
(...)
Does it have some effect on the electrons in a conductor that cause a charge to flow? (...)
As far as I know the charges are moved. That can be observed when a voltage source is used. When the magnetic field is changed in a conductor (the magnetic field lines 'go into' the conductor), so the needle of the voltage source moves to the positive pole. When the change of magnetic field is over (the magnetic field lines 'goes out' of the conductor) it can be observed that the needle of the voltage source moves to the negative pole for a moment before the needle comes back to 0. That is an evidence that the charge is in movement during changing.
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5 years ago
#6
I guess you already know that magnetic fields only apply a force directly onto moving objects, hence the confusion as to how magnetic fields create current?

As I understand it, the effect comes from something called the Maxwell-Faraday equation which states that for a varying magnetic field there is an associated electric field (which is also perpendicular to the magnetic field). This essentially arises from the fact that magnetism and electricity are two manifestations of the same thing, but without a solid mathematical background it's difficult to explain further. The mathematics in the equation which describes this interaction is far beyond what you'll know from GCSE, but you can find it here if you're interested:

When you have an electric field you can start pushing electrons through your wire - in other words, have a current.

Hope that helps!
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5 years ago
#7
I don't know whether you are still interested in this but here goes:

If an electron is in a magnetic field it won't move.
If an electron moves inside a magnetic field it will be deflected
From here we can say that a moving magnetic field is the same as a static magnetic field with moving conductor within it.
This is the same as my second point, so you can see that the electrons will be forced to move.
Thus, we have a current (only if the conductor forms a closed circuit).

Hope that helps
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5 years ago
#8
We think much alike, OP. Was previously doing this topic myself, couldn't really understand the whole electromagnetism topic at all to be honest. But, like you said, it has something to do with the fact that a force is applied onto the wire (carrying electrons) which causes the electrons to be moved one way which results in a potential difference.

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