What are the frequency and speed of a photon after scattering

[YMMMA]

Homework Statement

Photons incident upon free electrons that are essen- tially at rest are scattered by the electrons. As a consequence, the electrons gain kinetic energy. How do the frequency and speed of the photons present after the scattering compare to those present before the scattering?

Photon Frequency after scattering Photon Speed After scattering

(A) Lower Same
(B) Lower Less
(C) Same less
(D) Higher less
(E) Highe greater

Homework Equations

KE=hƒ-∅, where ∅ is the work function
Energy of a photon= hƒ= hc/λ, where c is the speed of light.

The Attempt at a Solution

[/B]
Photons speed doesn’t change, c is always constant. And ƒ and KE are proportional, so as the electron gain KE the photon loses its KE and so frequency decreases. It’s written in the answer key C, so I want to check if I am correct.

 

[TSny]

You are right. (A) is the correct answer.

Edit: We would not say that the photon has KE. It has electromagnetic energy. But I think you have the right idea.