# Amplitudes of Electromagnetic Waves Question

1. Jun 15, 2014

### Dick_Machine

So I can't find this anywhere, but I would really like an answer as it's driving me up a wall; Are the amplitudes of all electromagnetic waves the same, and if so how are the speeds of the particles that move along the wave not > c? Thanks in advance.

2. Jun 15, 2014

### Staff: Mentor

The amplitudes are not all the same.

I am not sure what you mean about particles moving along the wave.

3. Jun 15, 2014

### Dick_Machine

I meant, wave being the path of electrons/photons/(whatever particles E&M waves are made of) as they travel. I don't actually have any knowledge of this whatsoever so, sorry if it comes across confusing. Let me try again; in two space we have the sin x sin 2x sin 3x etc, but if I was traveling along any of them I would have to run at different speeds to get to the end at the same time. I was just wondering if the "stuff" an E&M wave was made of had some sort of component where it exceeded the speed of light.
However, since they don't have the same amplitudes then that makes more sense to me.

4. Jun 15, 2014

### Staff: Mentor

A photon is a particle only in the sense that the energy of the EM wave is transferred in "chunks". This little chunk of energy is what we call a photon. It is not moving with the EM wave, it is an inherent property of the EM wave itself.

In all reality, you're better off learning the classical description of an EM wave before ever worrying about photons. In classical physics an EM wave is a wave within the electromagnetic field. In this wave the strength and direction of the magnetic and electric field vectors alternate over time and propagate outward from the source. This can be seen by placing antennas at various distances from a transmitter and measuring the received signal.

5. Jun 15, 2014

### Staff: Mentor

It sounds like you are thinking of light as though it were composed of little pellets zipping along from place to place on sinusoidal paths. If so, your picture is pretty incorrect.

Classically, there are no particles, just the value and direction of the EM field which varies over time and space. The illustrations you may have seen that led you to your thought was not showing something moving in a sinusoidal path, it was showing a field which was different from place to place. It was stronger in some places and weaker in other places and pointing the opposite direction in yet other places. If you plot its strength along a straight line then you get a sinusoidal variation, but that is the value of the field at points along a straight line.

Quantum mechanically there are photons, but the rules concerning them are substantially more complicated.

6. Jun 15, 2014

### Dick_Machine

Ok I think I got it, but just to make sure: The wave itself is more of an "Area of Effect" mapping the highs and lows of the field, rather than being any physical track?

7. Jun 16, 2014

### Staff: Mentor

The field itself is a way of mapping out the interactions at any point in space. The wave is a variation in the field that obeys wave-mechanics.

See here: http://en.wikipedia.org/wiki/Field_(physics [Broken])

Last edited by a moderator: May 6, 2017