# What is the wavelength of the incident photon?

1. Oct 19, 2008

### roeb

1. The problem statement, all variables and given/known data
If the maximum energy imparted to an electron in Compton scattering is 45 keV. What is the wavelength of the incident photon?

2. Relevant equations

3. The attempt at a solution

$$\lambda_2 - \lambda_1 = h/mc (1 - cos \theta )$$
My first initial thought was to apply conservation of energy.

initial = final

hf + $$m_0 c^2$$ = $$m_0 c^2$$ + Ke + hf'
Where Ke = 45 keV (the kinetic energy of the scattered electron).
Since the problem states maximum energy, I thought that this would mean that theta = 90.

I then proceeded to get f - f' = 1.08 x 10^(19) Hz.

Then I was thinking well, since this is a maximum energy, why not say that f' = 0 (all of the photon's energy is absorbed, but then again that isn't really scattering is it?)

Unfortunately, using c = f $$\lambda$$ I still get the incorrect answer.

Does anyone know what I did incorrectly?

$$test$$

Last edited: Oct 19, 2008
2. Oct 20, 2008

### alphysicist

Hi roeb,

I believe this is an error. The maximum of the energy transferred to the electron does not occur when theta=90 degrees. Do you see what angle it needs to be instead?