# Can you change the wavelength of ligh without changing it's direction?

1. Apr 4, 2013

### Jarfi

So lets say we have a red light wave, can you have something particularly simple amplify it's wavelength, I know you could take a picture of it and send it out again the opposite side, but that's far sought. Oh and if an electromagnetic wave is absorbed by an atom, how exactly do you tell the kinetic energy(thus the wavelength) of the electron emitted?

And if long wavelength has too little energy too little energy to knock out electrons how are they detected? and if they can't even knock out electrons how do they ever cease to exist. I'm talking about low energy photons light radio waves or infrared waves, how exactly do these antennas work? is there no efficient way to catch or create very long wavelength light waves?

Oh and since you're here, the new pf layout looks pretty cheap, and the ads on top.. oh well maybe I'm just getting used to it.

2. Apr 4, 2013

### Staff: Mentor

Move towards the source and the wavelength will shorten; move away and it will increase. Although the speed of light in vacuum is always c no matter how you and the source move, the wavelength and the frequency will depend on the relative motion between you and the source.

There are many other ways of detecting electromagnetic radiation than looking for electrons being knocked out of atoms. For example:
- Even very very long-wavelength radio waves will create electric currents in a conductor (where there are plenty of free electrons floating await waiting for an electromagnetic wave to move them around).
- Absorption of infrared will slightly raise the temperature of the absorbing object, and this effect can be measured.

There are plenty of others ways as well; some googling will likely find them for you.

Last edited: Apr 4, 2013
3. Apr 4, 2013

### Staff: Mentor

What do you mean with "amplify its wavelength"?
If it passes a medium with a different refractive index, its wavelength will be different inside, but the frequency (and color) stays the same. If it hits a moving or oscillating object, there can be a slight frequency shift. If you want to change the color of light, you need something like wavelength shifters.

Depends on the setup. Measure its speed, measure how far it can go against an electric field, ...
Photoelectric effect? If no electrons are there, which electrons do you want to detect?
They can still give their energy to the electrons, which remain in the material.
Antennas are an efficient way to catch them.

4. Apr 4, 2013

### Jarfi

It says the wavelength shifter only lowers the wavelength, that's not quite enough.

The photoelectric effect? I was meaning wavelengths too low of energy that to happend, like in very low energy light wont affect the electrons since they never have the energy to knock them out.

They can lose energy to electrons without being absorbed? that's something I had not learned how happens, but it's commons sense in a way.

5. Apr 4, 2013

### Jarfi

However true, it's not something that will change the wavelength if my frame of reference stays the same relative to the frame of the light emitted.

6. Apr 4, 2013

### Staff: Mentor

If you are looking for something specific, please tell us what. It is annoying to guess what you are looking for.

As I said, "knocking them out" is not the only option. Actually, that is a very special interaction.

While this is true, it is completely unrelated to my previous post. They can get absorbed by the electrons, which stay in the material afterwards.