# The peak of the thermal radiation power spectrum (dR/dλ)

1. Feb 18, 2015

### Andres123

1. The problem statement, all variables and given/known data
The peak of the thermal radiation power spectrum (dR/dλ) is at a wacelength of about λm=hc/5kT. Why is the peak of the same power spectrum plotted as dR/df not at fm=c/λm= 5kT/h?

2. Relevant equations
dR/dλ= 2πhc2/(λ5(e(hc/λkT)-1))
f=c/λ

3. The attempt at a solution

2. Feb 19, 2015

### BvU

Hello Andres, welcome to PF

The idea at PF is that you post your efforts under attempt at solution and that helps us to guide you further as best we can. After all, you don't want someone else to do the exercise for you -- you want to learn by doing the exercise. See the guidelines for more info.

In the mean time: how do you find a peak ? What is the expression for dR/df ?

3. Feb 19, 2015

### Andres123

the equation for dR/df= 2πhf3/(c2(ehf/kt-1))
I am currently trying to differentiate both equation and setting them equal to zero to see if i find a relationship or reason for this. so far no success

4. Feb 20, 2015

### BvU

Also think about the relationship between df and d$\lambda$

I strongly advise you not to fall for this and explore by yourself. Spoilers are exactly what the name says.You are much better of thinking this over than getting the answer on a plate

Here is a thread from before you joined -- same subject. You see it's causing some confusion with others too...