Question 18: Why do not we observe Compton Effect with visible light?
Visible light photon possesses less energy, less momentum and less penetrating power. Therefore, when a visible light photon is incident on a metal, it loses all its energy in a single encounter with the electron.
As the rest mass of the photon is zero, therefore, it disappears and the energy transferred to the electron ejects it from the metal lattice. Therefore, we observe photoelectric effect.
For Compton Effect to happen, we need a photon that ejects electron from the atom and still has sufficient energy to retain itself (though with less energy) and scattered in some direction. This condition of sufficient energy is fulfilled in the case of X-rays or γ-rays photons which are far more energetic than the photon of visible light.