# Relation between photons and EM wave frequency

1. May 31, 2014

### humbleteleskop

Do individual photons have some attributes which relate to EM wave frequency? In other words, is there any difference in photons composing a red and blue beam of light?

2. Jun 1, 2014

### Matterwave

Certainly, photons composing blue light have a higher frequency which means they have a higher momentum, and a higher energy.

3. Jun 1, 2014

### humbleteleskop

I didn't think frequency could be attributed to individual photons.

How do we differentiate 1,000 photons each having energy E, from 2,000 photons having energy E/2? What would be the instrument or type of sensor that could tell that difference?

4. Jun 1, 2014

### UltrafastPED

If all of the photons hit at the same time, and in the same small area, you could get multi-photon absorption - 1,2,3, or more photons absorbed by each process. But the statistics will not be uniform, so you can tell; but this requires the conditions when non-linear optics is required.

The photo-electric effect (see Einstein, 1905: http://en.wikipedia.org/wiki/Photoelectric_effect) applies in most ordinary circumstances - and then the metal plate has no trouble telling the difference between photons with energy higher than the work function barrier, and those below.

5. Jun 1, 2014

### humbleteleskop

Interesting. Especially the part how neither amplitude nor wavelength are responsible for the effect, but frequency alone. Which doesn't really make sense to me as I understand all three are proportionally correlated, so I don't see how frequency can be independent of the other two in such way.

6. Jun 1, 2014

### Staff: Mentor

Wavelength and frequency are (of course) correlated, but amplitude can be varied independently. The surprising and counterintuitive thing about the the photoelectric effect is that it doesn't matter how much you dial up the amplitude and therefore how much energy is transferred to the target - you won't get any electron emission if the frequency is too low (equivalently, if the wavelength is too great).

7. Jun 1, 2014

### Jilang

Yes, I always thought that the wavelength was c/f. I don't think a single photon had an amplitude though.

8. Jun 1, 2014

### Staff: Mentor

It doesn't. Electromagnetic radiation has an amplitude, and that determines (sort of) the number of photons.