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# Help with Magnetic Fields Watch

1. Hi I have 2 questions about putting a bar magnet into a coil provided the coil is a completer circuit with an ammeter attached.

1. Does the magnetic field of the bar induce and emf in the coil which in turn induces a current? So does an induced emf cause a current to flow or are they independent?

2. How would the ammeter act when you put the bar in the coil and then came to rest inside the coil? Ammeter would deflect and got back to zero or, it would deflect then all back to a lower reading?
2. bump any help really appreciated
3. (Original post by SirRaza97)
Hi I have 2 questions about putting a bar magnet into a coil provided the coil is a completer circuit with an ammeter attached.

1. Does the magnetic field of the bar induce and emf in the coil which in turn induces a current? So does an induced emf cause a current to flow or are they independent?

2. How would the ammeter act when you put the bar in the coil and then came to rest inside the coil? Ammeter would deflect and got back to zero or, it would deflect then all back to a lower reading?
1). The movement of the bar magnet into the coil causes a current to flow. This is due to the motion causing a changing magnetic field through the coil. The corresponding emf required to cause this current is called an induced emf.

2). A current is induced only when the magnet is moving in the coil. If you hold the magnet inside the coil and keep it stationary, no current will be induced. Equally, you could move the coil which would cause a change in current.

I hope this makes sense.
4. (Original post by hezzlington)
1). The movement of the bar magnet into the coil causes a current to flow, the corresponding emf required to cause this current is called an induced emf.

2). A current is induced only when the magnet is moving in the coil. If you hold the magnet inside the coil and keep it stationary, no current will be induced. Equally, you could move the coil which would cause a change in current.
Thanks. So when you move a magnet into a coil and keep it at rest then the ammeter would deflect and then fall back to zero right?
5. (Original post by SirRaza97)
Thanks. So when you move a magnet into a coil and keep it at rest then the ammeter would deflect and then fall back to zero right?

I believe Faraday and Joseph Henry carried out this exact experiment in the 1830s. Might be worth having a google if you want to read more about it.

Any other questions and I'd be happy to help.
6. (Original post by hezzlington)

I believe Faraday and Joseph Henry carried out this exact experiment in the 1830s. Might be worth having a google if you want to read more about it.

Any other questions and I'd be happy to help.
Just one more question. Say I had a system where there was a constant production of induced currents which in turn produced a magnetic field which in turn produced an induced current and so on. Does the strength of the magnetic field and the magnitude of current decrease as we go further on? What are these effected by if that is the case?
7. (Original post by SirRaza97)
Just one more question. Say I had a system where there was a constant production of induced currents which in turn produced a magnetic field which in turn produced an induced current and so on. Does the strength of the magnetic field and the magnitude of current decrease as we go further on? What are these effected by if that is the case?
Hmm, I don't really get the question.

Can you give me a physical example of a system where this occurs?
8. (Original post by hezzlington)
Hmm, I don't really get the question.

Can you give me a physical example of a system where this occurs?
I couldn't give you an example, I made it up. So say I magnet being mechanically pushed into and out of a coil. This coil has an indcued current which would cause it to have a magnetic field itself right? This alternating magnetic field causes another current in another coil. So on and so forth. Will the strength of the field get weaker? This kind of system may not be actually possible btw.
9. (Original post by SirRaza97)
I couldn't give you an example, I made it up. So say I magnet being mechanically pushed into and out of a coil. This coil has an indcued current which would cause it to have a magnetic field itself right? This alternating magnetic field causes another current in another coil. So on and so forth. Will the strength of the field get weaker? This kind of system may not be actually possible btw.
It's not the magnetic field that induces a current. It's the changing of the magnetic field through the coil that generates this current. If you are asking what would happen if you placed a second coil in proximity to the bar magnet/coil system, and are trying to generate a current by using the magnetic field created through the bar magnet/coil system, well..I don't think this would work?
10. (Original post by SirRaza97)
I couldn't give you an example, I made it up. So say I magnet being mechanically pushed into and out of a coil. This coil has an indcued current which would cause it to have a magnetic field itself right? This alternating magnetic field causes another current in another coil. So on and so forth. Will the strength of the field get weaker? This kind of system may not be actually possible btw.
I know what you are saying and yes the magnetic field will get weaker because the induced magnetic field from the changing current will never be as strong the magnetic field which induces the current its self

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