Photoelectric Effect

Predictions of the Wave Theory - the light intensity should influence the maximum KE of electrons; - the frequency of the light should not affect the KE of ejected electrons.

Photon Theory Light is a particle again… E=hf

The energy of photon is the same for all photons in a monochromatic beam. Increasing of the intensity of the light means increasing of the number of photons in the beam, but does not affect the energy of each photon as long as the frequency is not changed.

According to Einstein, electron is ejected from the metal by a collision with a single photon.

An increase in intensity of the light beam means more photons are incident, so more electrons will be ejected , but max KE in not changed. If the frequency of the light is increased, the max KE increases linearly. If the frequency f is less than the “cutoff’ frequency f0, no electrons will be ejected at all, no matter how big is the intensity.

Compton Effect

Photon Interaction A photon can be scattered (Compton effect). A photon may knock an electron out of an atom (Photoelectric effect). A photon may knock an electron to a higher energy state in the atom (excited state of the atom). A photon can actually create matter (pair production).

Pair Production What is (a) the minimum of a photon, that can produce an electron-positron pair? (b) What is this photon’s wavelength?

Wave-Particle Duality

Wave Nature of Matter

De Broglie Wavelength