Energy lost when current is induced in a loop

[Northprairieman]

Hi there,

If a proton passes through a loop of wire, it induces a tiny current in the wire. Will the proton lose energy and slow down as a result of this?

If so, by how much?

 

[asdofindia]

The proton will slow down.

I think I²R will be the energy lost by the proton.

 

[Bill_K]

If a proton passes through a loop of wire, it induces a tiny current in the wire.

Forgive me, but I am finding this statement hard to accept. Thanks to the proton there will be an E field, axially symmetric and forward pointing, with a radially outward component. There will also be a B field, axially symmetric and pointing along the circumference. I don't see how either of these fields will induce a current in the wire.

If you tried the same experiment using the pole of a magnet instead of the proton, *then* you will induce a current in the wire. Is that what you're thinking of??

 

[asdofindia]

oh yeah. i had it wrong.
proton is just a current. it'll induce a magnetic field around. no electric field. you're right. it won't slow down assuming the loops is uniformly neutral.

 

[Northprairieman]

Thanks for the responses. So what if you had a stream of protons? Would that be equivalent to the pole of a magnet?

In this stream of protons, will each successive proton be slowed down because the proton before it passing through the loop made the loop of wire no longer uniformly neutral?

 

[epsilonjon]

Thanks for the responses. So what if you had a stream of protons? Would that be equivalent to the pole of a magnet?

In this stream of protons, will each successive proton be slowed down because the proton before it passing through the loop made the loop of wire no longer uniformly neutral?

Whether it's a stream of protons or a single proton, it won't make any difference will it? There will still be no current induced because there is no changing magnetic flux through the loop.

 

[cragar]

ya if you just had a steady stream of protons, you would have a static B field and it wouldn't induce a current. And if you had just one proton moving I am not sure if this counts as a current, I think i remember reading something about this in Griffiths.

 

[Northprairieman]

So according to this post:

https://www.physicsforums.com/showthread.php?t=487014

In the little diagram there, it shows a B field generated by a moving charge. So if I understand this correctly, that's a "static" B-field (not a moving B-field) and hence does not produce a magnetic flux?

What if the charge were accelerating?

 

[willem2]

So according to this post:

https://www.physicsforums.com/showthread.php?t=487014

In the little diagram there, it shows a B field generated by a moving charge. So if I understand this correctly, that's a "static" B-field (not a moving B-field) and hence does not produce a magnetic flux?

The B-field is static in the reference frame of the electron. For a stationary object, the B-field
will increase if the electron approaches, and decrease when it moves away again.
You will get a current that slows down the electron, but if the electron goes through the loop of wire, there won't be any magnetic flux at all going through the loop.