# Energy and Boltzmann's Constant

1. May 14, 2006

### prolong199

I have to find the average kinetic energy of a photon on the sun, given that E=kT where k=Boltzmann's Constant and the internal temperature of the sun is 15x10^6K. Can someone please leed me in the right direction, thanks.

2. May 14, 2006

### Icheb

Am I wrong in assuming that it would just be

$$E=E_{kin}$$
$$kT=mv^2$$

3. May 15, 2006

### Andrew Mason

The question is poorly worded. Kinetic energy suggests that the photon's energy is due to motion. A photon has only one speed: c. It has only one kind of energy: E = $h\nu$.

The energy of a photon from the sun is determined by the sun's temperature. The Planck Law blackbody spectrum gives the energy distribution of a blackbody as a function of that body's temperature. The peak of the blackbody spectrum curve is the energy of the photon you are looking for. Wien's Displacement law will give you that photon energy (the peak of the Planck Law distribution curve).

AM