# Electromagnetic waves

kent davidge
Is it correct to say a varying electric field creates a magnetic field and vice-versa instead of saying that a charge creates such fields?

## Answers and Replies

Mentor
Is it correct to say a varying electric field creates a magnetic field and vice-versa instead of saying that a charge creates such fields?
"As well as" would work better than "instead of":
- A varying electrical field will produce a magnetic field.
- A varying magnetic field will produce an electrical field.
- Electrical charges will produce an electrical field.

Google for "Maxwell's equations" if you want to see the real thing.

reyya_42
"As well as" would work better than "instead of":
- A varying electrical field will produce a magnetic field.
- A varying magnetic field will produce an electrical field.
- Electrical charges will produce an electrical field.

Google for "Maxwell's equations" if you want to see the real thing.

+ Moving electrical charges will produce a magnetic field.

kent davidge
(i don't speak english well) Oh yes. I'd never been confortable with the idea that a field creates another in space without existing a charge. Then I realize that whenever there is a field, there is a charge that produces that field in somewhere (maybe very far away). But once a field exists and varies, it can produces the other field. Then my conclusion was that there must be one charge to create the first field, then such field varying (thanks to the moviment of the charge) will produce the other field independently of the charge. Is this conclusion correct?

Science Advisor
Charges do create fields, but you can also have fields without charges. For example, annihilation of matter and antimatter will create photons. I don't think the matter and antimatter have to be charged for this to occur. You can also get Hawking radiation from uncharged black holes.

kent davidge
But matter is composed of electrical charges , is it not so?

Staff Emeritus
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But matter is composed of electrical charges , is it not so?

Neutrino is one example of "matter" that has no charge. So that criteria is not valid.

Zz.

kent davidge
oh ok. and do neutrinos emit electromagnetic waves?

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oh ok. and do neutrinos emit electromagnetic waves?

It has a magnetic dipole.

Zz.

kent davidge
Soooo, anyway there must be a "body" which first creates a field. In this case the "body" is the neutrino, no??

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Soooo, anyway there must be a "body" which first creates a field. In this case the "body" is the neutrino, no??

I'm not sure what you are getting at, because it appears as if you're making things up as you go along. First you insist that all matter must be made of charge. Now that that has been shown to be wrong, you now want to have a "body" being present.

What are you trying to argue for, here? That ALL E&M fields must have some sort of a "source" that creates them? How far back in time and space do you want to trace this source? I can show you an accelerating structure for a particle accelerator where the "source" is no where near this structure, and yet, we have a waveguide containing an EM field.

Someone earlier mentioned that you should look into Maxwell equations. Have you done that yet?

Zz.

kent davidge
Yes, I'm trying to say that it would be there a source of a electric or a magnetic field, but only for the first field (electric or magnetic) to be created. Then this field changing would create the second. Example: in a magnet we have a magnetic field, created by the charges arrangement. This field changing creates a electric field, as you know.
You recommended me to look at the Maxwell equations... yes, those equations tell us a lot about the behavior of the fields, but what I'm wondering is if you go back in space you'll find a source that is generating at least one of them.

Staff Emeritus
Yes, I'm trying to say that it would be there a source of a electric or a magnetic field, but only for the first field (electric or magnetic) to be created. Then this field changing would create the second. Example: in a magnet we have a magnetic field, created by the charges arrangement. This field changing creates a electric field, as you know.
You recommended me to look at the Maxwell equations... yes, those equations tell us a lot about the behavior of the fields, but what I'm wondering is if you go back in space you'll find a source that is generating at least one of them.

Sorry, nope. The real field in physics is electromagnetic. Electric and magnetic are ways to view the electromagnetic field. They are not independent.

I suggest you spend some time on Wikipedia reading about electromagnetic fields.

kent davidge
Ok, so let us imagine our universe with no charges. Would we still have a electric or a magnetic field in some point of the universe?

Science Advisor
You can still have neutrino annihilations and black holes without charges.

Staff Emeritus
A photon has no charge. I can't think of any physics that says that a photon 's life must have a beginning or an end.

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Ok, so let us imagine our universe with no charges. Would we still have a electric or a magnetic field in some point of the universe?

Where exactly did you stop understanding the fact that I presented regarding neutrinos? It has ZERO mass, and yet, it has a magnetic moment. Is it because you didn't have an appreciation what "having a magnetic moment" actually means? This is something that behaves as if it is a "bar magnet", to put crudely, and implies that if I have a sensitive enough Gauss meter, I can detect a magnetic field from it.

Yet, it is NO CHARGE!

I have just repeated what I had told you already.

Now, have we answered your question?

Zz,.

kent davidge
Ok. I think I did not express my thoughts well.

It has ZERO mass
Wikipedia and others sources of information says that neutrinos have mass.

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Ok. I think I did not express my thoughts well.

Wikipedia and others sources of information says that neutrinos have mass.

It was a typo. It should read zero CHARGE.

Zz.

kent davidge
It's interesting how the em field is stated by Wikipedia: "An electromagnetic field (also EM field) is a physical field produced by electrically charged objects".

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It's interesting how the em field is stated by Wikipedia: "An electromagnetic field (also EM field) is a physical field produced by electrically charged objects".

And as we all know, Wikipedia is never wrong.

Zz.

davenn
kent davidge
lol