Do Electric and Magnetic Fields Affect Electromagnetic Waves?

[faiz4000]

why do electric and magnetic fields have no effect on an electromagnetic wave?

 

[Antiphon]

Electric fields exert forces on charges. Magnetic fields exert forces on currents (or moving charges.).

Neither field exerts forces on electric or magnetic fields. This is the classical statement of the linearity of EM fields and to a very large degree it is accurate.

 

[Hernik]

Is it because the electromagnetic wave has no charge?

 

[Dr Lots-o'watts]

why do electric and magnetic fields have no effect on an electromagnetic wave?

A wave is also a field. A field does not act on another field just like a force does not act on another force. :)

 

[Antiphon]

Is it because the electromagnetic wave has no charge?

Yes. But there is an exception; some electromagnetic (electroweak) fields can carry charge but these fields are almost never observed directly.

 

[Vanadium 50]

I think I am not sure I agree.

A field is just a set of numbers at each point in space and time. We think of electric and magnetic fields, but the same formalism can be used elsewhere: in a previous message I described wind as a velocity field. So there is no reason a field cannot act on another field, and there are counterexamples: a changing electric field produces a magnetic field.

 

[Dr Lots-o'watts]

So there is no reason a field cannot act on another field, and there are counterexamples: a changing electric field produces a magnetic field.

An electric field cannot act on another electric field. The same holds for other classical force-fields anyway.

 

[Vanadium 50]

That's true, but the key word is "electric". It's a statement about the kinds of fields, not a statement about fields.

 

[Antiphon]

That's true, but the key word is "electric". It's a statement about the kinds of fields, not a statement about fields.

This is correct in the general case.

When photons are involved and we have Maxwell's equations, the charges don't exert forces on the fields only the other charges.

The electroweak fields are different. The W is a charged force carrier. This means the electroweak fields do exert forces on charges, on EM fields, and on itself.

 

[mvan4310]

So an electromagnetic field couldn't say, disturb light, or any other frequency on the EM Spectrum?

Any one force not having an affect on the other is incorrect, look at gravity, it has an affect on electromagnetism.

Michael