# UV Catastrophe

1. Apr 20, 2013

### |mathematix|

So people thought that as wavelength increases for electromagnetic radiation, intensity of radiation increases but this would mean that people would melt if exposed to any radiation higher than visible light. But then they did an experiment and they sketched the graph of the experiment which is the true graph of intensity vs wavelength.

I get everything up to this point but I would very much appreciate it if someone explains to my why intensity would decrease after the peak intensity at the visible light range? What does it have to do with quantification of energy? Also, what is the proper derivation of E=hf?
I really want to have a complete understanding of this because it is very important to understand Einsteins explanation of the photo electric effect and the the rest of quantum mechanics.

Thank you!

2. Apr 20, 2013

### Staff: Mentor

To get ultraviolet light in quantum mechanics, you need some minimal amount of energy - the energy of a photon. This rarely happens, so the total energy emitted as ultraviolet radiation is finite.
In classical thermodynamics, this minimal amount is not required - you would expect that everything, everywhere, would emit a lot of ultraviolet radiation.

3. Apr 20, 2013

### |mathematix|

Why does it rarely happen?

4. Apr 20, 2013

### Staff: Mentor

If the average energy per particle is something like 0.1 eV , particles with an energy of 3 eV and more are rare.
(if you don't know eV: does not matter, just compare 3 and 0.1)

5. Apr 20, 2013

### |mathematix|

Ok, thank you!
eV is electron volt isn't it?

6. Apr 20, 2013

yes.