The details of the photoelectric effect were in direct contradiction to the expectations of very well developed classical physics.
The explanation marked one of the major steps toward quantum theory.
The remarkable aspects of the photoelectric effect when it was first observed were:
|1. The electrons were emitted immediately - no time lag!|
|2. Increasing the intensity of the light increased the number of photoelectrons, but not their maximum kinetic energy!|
|3. Red light will not cause the ejection of electrons, no matter what the intensity!|
|4. A weak violet light will eject only a few electrons, but their maximum kinetic energies are greater than those for intense light of longer wavelengths!|