# Electromagnetic waves

1. Feb 15, 2016

### 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?

2. Feb 15, 2016

### Staff: Mentor

"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.

3. Feb 15, 2016

### reyya_42

+ Moving electrical charges will produce a magnetic field.

4. Feb 15, 2016

### kent davidge

(i dont 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?

5. Feb 15, 2016

### Khashishi

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.

6. Feb 15, 2016

### kent davidge

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

7. Feb 15, 2016

### ZapperZ

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

Zz.

8. Feb 15, 2016

### kent davidge

oh ok. and do neutrinos emit electromagnetic waves?

9. Feb 15, 2016

### ZapperZ

Staff Emeritus
It has a magnetic dipole.

Zz.

10. Feb 15, 2016

### kent davidge

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

11. Feb 15, 2016

### ZapperZ

Staff Emeritus
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.

12. Feb 15, 2016

### 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.

13. Feb 15, 2016

### Staff: Mentor

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.

14. Feb 15, 2016

### 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?

15. Feb 15, 2016

### Khashishi

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

16. Feb 15, 2016

### Staff: Mentor

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.

17. Feb 15, 2016

### ZapperZ

Staff Emeritus
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,.

18. Feb 15, 2016

### kent davidge

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

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

19. Feb 15, 2016

### ZapperZ

Staff Emeritus
It was a typo. It should read zero CHARGE.

Zz.

20. Feb 15, 2016

### 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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