"Quantum" is a scary word, but is really only means "quantity". The most significant discreet quantity is in Planck's quantum hypothesis for photon energy:
E = nhƒ
in which the integer n quantizes light such that you cannot have fractional photons.
The graph shows the wavelength of light bombarding blackbodies of certain temperatures, and the intensity of light radiated from the blackbody. Wien's Law tells what wavelength makes a blackbody radiate the most intense light, at a certain temperature T.
When light shines onto the curved metal plate, it emits electrons and causes a current to run through the setup. The voltage supplied to oppose this current is the stopping potential. This voltage and the electron's charge would be the electron's kinetic energy.
The classical understanding of radiation is that when sufficient energy builds up, a particle breaks free of the object. Intuitively, a metal would eventually radiate if a light is shined on it long enough. Experiments on this photoelectric effect show that the only way to get a metal to radiate is to shine a light of high enough frequency, no matter how intense or prolonged the light.
The work function is the energy required to remove an electron. In accordance with experimental results, there is a certain light frequency that must be achieved before an electron can escape.
There are four ways in which particles can interact:
1) photoelectric effect
2) electron excitation
3) Compton effect
4) pair production
This is pair production:
Light hits a nucleus and forms a positron and electron. Charge and momentum are conserved. Beautiful.
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