# HELP in Quantum Physics.

1. Mar 24, 2006

### prochatz

Hello,

1)I want to prove that the number of photons emitted per unit of surface of black body, per unit of time and per unit of space of frequency is:

n(v,T)=(2*π*v^2)/[c^2*exp(h*v/k*T) - 1]
Any ideas?! :uhh:

2)How can I find the wavelength as a function of the kinetic energy i)for photons, ii)for electrons?

i)For photons.
Look what I've done so far. I used the relation: E^2=c^2*p^2+(mc^2)^2
The photon's rest mass is 0. So we get: E=c*p
p=E/c ---> p=h*v/c --->p=h/λ
Finally: λ=c*h/E

ii)For electrons.
I don't know what to do Do you think that I should use the photoelectric equation (E=h*v - W)???

I appreciate any help.
Thank you.

2. Mar 25, 2006

### gulsen

1. Feynman Lectures on Physics deal the question in chapter 41 of volume 1. (AFIK, you need to own the book to download legally).

2. You can use de Bröglie wavelength for finding$$p(\lambda)$$. From special relativity, you can relate momentum & kinetic energy.

$$p = \frac{h}{\lambda}$$
$$E^2 = (pc)^2 + (mc^2)^2$$

Last edited: Mar 25, 2006
3. Mar 26, 2006

### nrqed

well, you must have *some* starting point. what do you know about bb radiation? What formula did you see in class? What textbook are you using? It's hard to answer without knowing what you already know.

Pat

4. May 7, 2006