# EM waves

1. Aug 8, 2014

### EEngineer91

Hi,

I have a few question about EM waves. What is an EM wave composed of? Are the E and B field lines real or imaginary. .. if it is an wave what is waving? (Eg water is waving in tsunami)

wouldn't a pulsating chargr produce a electric pressure wave?

2. Aug 8, 2014

### Drakkith

Staff Emeritus
An EM wave is composed of alternating electric and magnetic field vectors. That is, the direction and magnitude of the electric and magnetic fields are fluctuating and changing direction over time. Note that field lines are not "real" objects but merely a way of helping us visualize the fields. They are like the contour lines that show you the elevation of terrain on a map.

I don't know what an electric pressure wave is. An AC or pulsating DC voltage source with generate EM waves within the circuit it is connected to.

3. Aug 8, 2014

### sophiecentaur

The lines of force are just a way of representing the fields. An EM wave is 'composed of' varying E and B fields which propagate through space or a medium. The name "wave" tells you that EM waves share a number of characteristics with other, visible mechanical waves. In the case of EM waves, nothing actually needs to wave about, though. No movement is involved with waves moving through empty space but charged particles are sometimes measurably displaced as an EM wave moves through a 'medium'.

I'm not sure what sort of "pulsating Charger" you mean but when you switch an electric current on and off, an EM pulse will radiate out into space. You may have heard 'click' interference on a radio when a heater is switched on and off and everyone will have heard the sort of interference that old car ignition systems can cause on weak radio signals.

4. Aug 8, 2014

### EEngineer91

So EM waves (real) are composed of things we do not consider real (E and B induction)?

An electric pressure wave is the same as an air pressure wave...a non - transverse wave

5. Aug 8, 2014

### EEngineer91

That's my point...they need a medium to propagate...the virtual photon flux field....or quantum vacuum

6. Aug 8, 2014

### sophiecentaur

Of course we consider them as "real". Reality doesn't have to involve mechanical movement.
I don't know what you mean by "Electrical Pressure Wave". What is the context of that term? Are you referring to piezo electric distortion?

7. Aug 8, 2014

### sophiecentaur

I think you need to describe your level of actual knowledge of this topic. Do you know what a virtual photon flux field is? You may just be trying to jump too far in one go.

8. Aug 8, 2014

### EEngineer91

Imagine an air pressure wave...now replace the air with E and B field lines.....a electro pressure waave....with longiudinal propagatiion

9. Aug 8, 2014

### EEngineer91

Yes, I have a bachelors degree in physics thanks

10. Aug 8, 2014

### sophiecentaur

So you will know about Maxwell's equations and the solution which gives a propagating EM wave? The fields are transverse for a plane wave. In situations near a conducting structure (tied waves etc) the field may be longitudinal.
The situation with a mechanical pressure wave is very different, that can be longitudinal or transverse and it is risky to try to draw too many conclusions about EM waves from what you know about mechanical waves.

You have confused me because you have used a term "quantum vacuum" yet you seem to be wanting a very mechanical model for your EM waves.

11. Aug 8, 2014

### EEngineer91

Well, maxwell equations give no longitudinal waves only in free, empty space. Empirically, space is not free or empty but prevaded by a sea of virual photons popping in and out of existence

12. Aug 8, 2014

### sophiecentaur

So you want an Advanced Physics discussion but using mechanical models? You can have one or the other but not both, I think.

13. Aug 8, 2014

### EEngineer91

Im sorry you think those two concepts are mutually exclusive....the fact is they must be interrelated

14. Aug 8, 2014

### Drakkith

Staff Emeritus
This can occur in conductors where there are charges that are able to move in response to the applied fields, but there is no such thing in free space. EM waves in free space are transverse waves.

15. Aug 8, 2014

### nsaspook

So what would be changed in our understanding of EM waves if scalar longitudinal waves existed in some virtual medium?

16. Aug 8, 2014

### EEngineer91

Well, our understanding would go beyond standard theory and you could produce non-linear effects. ..propagation of em waves relates to velocity of light...all this could not apply to non-transverse waves since photons are only transverse...and like I said for empty space derivation there is no such thing as free (empty) space so these derivations are a limiting and special case...you claim these field lines have no reality but em waves do....this is not consistent

17. Aug 8, 2014

### Drakkith

Staff Emeritus
I can't even understand what you're trying to get at. It appears to make absolutely no sense.

Also, field lines are visual representations of what the field is doing. They allow us to visualize the force that the field will apply to charged particles. That's all they do. The wave itself does not consist of field lines.

18. Aug 8, 2014

### sophiecentaur

I think it's time you provided some reference or experimental evidence for your opinion here. (It is not text book stuff). That is what us needed for PF. Opinions are not really accepted without some backup. Read the forum rules.

19. Aug 8, 2014

### nsaspook

So are you saying these waves could transmit information at FTL speeds or counter the laws of thermodynamics and relativity?

20. Aug 8, 2014

### EEngineer91

I simply ask what is waving in an em wave...I hear its field lines but these are not real but em waves are lol