# Energy Density of Sunlight

1. Feb 10, 2008

### theinfojunkie

[SOLVED] Energy Density of Sunlight

1. The problem statement, all variables and given/known data
Use the solar constant (1350 W/m^2) to calculate the energy density of sunlight at a)Earth and b) near the surface of the sun.

2. Relevant equations
Stefan-Boltzman = (2pi^5)/(15(h^3)(c^2))
h=6.63x10^-34 j.s
L(solar luminosity)=4pi(D^2)S
S=1340 W/m^2

3. The attempt at a solution
I don't know what I'm doing. I'm assuming those are the more important things to use.
I'm getting frustrated with this and really need some help. I'm trying to plug in the power per area into the stefan boltzman eq to see if I can find the answer but it isn't working.

2. Feb 10, 2008

### theinfojunkie

Could I use Planks formula or Raleight Jeanes law to solve this? Since the wavelength is rather large, I'm thinking I could, but I'm not sure how to apply it.

Last edited: Feb 10, 2008
3. Feb 11, 2008

### theinfojunkie

dR/D(lambda)=dU/d(lambda)(4/c)
du=4dR/c
integrate
u=4R/c

where R is 1350(solar constant) and gives the energy density on earth.

for part b

L=4pir^2 S(solar constant)
S=L(luminosity)/4pir(of the sun)^2
then u=4r/c where R=S