Making electromagnetic wave

1. Feb 18, 2013

Markovnikov ya

Can I assume that anything with high enough speed will generate electromagnetic wave? Photons are not charged. But maybe because they move fast enough, they generate vortex electric field, since this field is changing, then you have a corresponding magnetic field with it, so you have an electromagnetic wave. So, if the speed of the particle is fast enough, you can generate electric field without the particle being charged?

So, can I say that a photon is simply a very small particle moving very fast, and generating electromagnetic wave?

Or ,maybe photons are particles of vacuum?

Last edited: Feb 18, 2013
2. Feb 18, 2013

Staff: Mentor

No, an EM wave is not generated by moving charges, but by accelerated charges.

Don't mix photons with classical EM waves until you know everything you can about the latter. Otherwise you will only confuse yourself. I know this from experience!

You cannot. Photons are not little particles moving quickly through space. They do not travel like bullets from a gun. They are the quantized interaction of the EM wave with matter. This just means that if you measure the energy of an EM wave you will find that it is transferred in "chunks", and not in a continuous manner.

They are not.

3. Feb 18, 2013

Markovnikov ya

What is the charge then? the photon is the one who provides interaction between charges, but what is it in the charge that makes photon "move"?

Can I assume that field lines are moving photons?

Are field lines like the wind and photons like the moving sand? Only to move each grain of sand you need the wind to be able to force each grain to move with a speed of light?

Last edited: Feb 18, 2013
4. Feb 18, 2013

Staff: Mentor

There isn't one. Photons move at c though a vacuum always. Charges do not make them move like they would do for another charged particle.

Absolutely not. Field lines are representations of the electric or magnetic field. They do not actually exist. They simply aid us in visualizing what a particle or other object will do when placed in a field.

The best thing you can do right now is to absolutely forget everything you know about photons. I guarantee you it is not correct and will only confuse you. Then, study up on what a classical EM wave is and why it behaves the way it does.

5. Feb 18, 2013

Markovnikov ya

ok, will do so, thank you:)

6. Feb 18, 2013

Markovnikov ya

I am trying to understand light, it is so weird. Light is not an electromagnetic wave, since it has different speed in different mediums. Light does not have mass (the mass that can be derived from the energy is not a real mass), so its not a particle either. What is it?

Back to my original question about EM wave being a matter. Well, it has energy, it has speed of distribution, it exerts pressure on reflecting or absorbing particles, so it must have a mechanical momentum, if it has momentum, then it must have mass. So it has all the components necessary to be considered matter. But its speed in any medium is the speed of light. But you cannot say the same thing about light, its speed changes with change in refractive index of the medium.

Ok, you are saying that electromagnetic wave is a lot of photons. But the waves' speed changes as the refractive index of the medium changes. Yet photons can only exist while moving with the speed of light. Maybe that is where some of the photons are absorbed by the medium (or reflected). Yet the light still exists (because some photons got through the medium without change in speed?), only with smaller intensity? But then I don't understand. EM wave moves in any medium with a speed of light, no matter what the refractive index is. Then why doesn't the EM wave of light disappear when some photons are absorbed?

I guess the question would be: WHy is any light absorbed at all if EM wave is supposed to travel at a speed of light through all mediums? It means that light is not EM at all! my head hurts.
Or does it mean that light is light and EM wave is EM wave. And classical EM wave does not have any photons?

7. Feb 18, 2013

Staff: Mentor

Light is most certainly an EM wave. It has a wavelength between 350 and 700 nanometers or so. This is much much smaller than something like a radio wave for an FM station, which has a wavelength measured in whole meters.

Not true. All EM waves have a reduced velocity when traveling through a medium. And they do not have mass.

Photons exist whenever you have an EM wave, no matter how fast its moving or what its moving through.

In classical physics photons do not exist. An EM wave is solely the changing electric and magnetic fields propagating through space. Quantum Mechanics, and later Quantum Electrodynamics explains EM waves as photons and is much more accurate than classical physics.

It would greatly help your understanding if you forget about photons altogether for now and just get the basics of a classical EM wave down.

8. Feb 18, 2013

Markovnikov ya

Hold on, so classical EM wave has different velocities in different mediums?

9. Feb 18, 2013

Staff: Mentor

Absolutely.

10. Feb 18, 2013

Markovnikov ya

You are saying that EM waves do not have mass.
But lets say we have a medium and a wave is absorbed. Doesn't it mean that the wave must put pressure on the particle in order to be absorbed? i mean, if you have electric and magnetic fields in a EM wave, then electric field would cause some small current and then magnetic field would influence these small currents, directing them into the medium, which would cause pressure. And if you have something that can cause pressure, doesn't it mean that the electric field in the EM wave has momentum. And then if you have momentum, wouldn't that mean that the object has mass?

Also, if EM wave always has photons, then does it mean that EM wave can only exist when its' speed is equal or greater than the speed of light?

Last edited: Feb 18, 2013
11. Feb 18, 2013

Staff: Mentor

No. Photons (or the EM wave, whichever way you look at it) carry momentum but have no mass.

A photon is the quantized interaction of an EM wave. It is not some little particle that just happens to travel along with the wave. And how could an EM wave's speed be greater than the speed of light when the EM wave itself IS light?

12. Feb 18, 2013

Markovnikov ya

ok, thank you. I'll keep on studying:)