Chapter 27, Problem 11Q

To determine

What is the difference between photoelectric effects and Compton effect?

Answer to Problem 11Q

Solution:

The difference explained below.

Explanation of Solution

The photoelectric effect:

Photons have no mass, but they have momentum and they have an energy given by:

Energy of a photon $E=h\upsilon$

The photoelectric effect works like this. If you shine light of high enough energy on to a metal, electrons will be emitted from the metal. Light below a certain threshold frequency, no matter how intense, will not cause any electrons to be emitted. Light above the threshold frequency, even if it's not very intense, will always cause electrons to be emitted.

The Compton effect:

Although photons have no mass, they do have momentum, given by:

Momentum of a photon

$p=\frac{E}{c}=\frac{h\upsilon }{c}=\frac{h}{\lambda }$

Convincing evidence for the fact that photons have momentum can be seen when a photon collides with a stationary electron. Some of the energy and momentum is transferred to the electron (this is known as the Compton effect), but both energy and momentum are conserved in such a collision.