What are the main two experimental observation of photoelectric effect that are against classical physics?

1. The first main experimental observation of the photoelectric effect that is against classical physics is the fact that the kinetic energy of the emitted electrons is independent of the intensity of the incident light, but depends only on the frequency of the light. According to classical physics, the energy of the electrons should increase with the intensity of the light, as more intense light should transfer more energy to the electrons.

2. The second main experimental observation of the photoelectric effect that is against classical physics is the existence of a threshold frequency below which no electrons are emitted, regardless of the intensity of the incident light. According to classical physics, electrons should be emitted as long as the intensity of the light is above a certain threshold, regardless of the frequency of the light.

1. The independence of the maximum kinetic energy of the emitted electrons from the intensity of the incident light: In classical physics, the energy of the incident light should be proportional to the intensity of the light. However, in the photoelectric effect, the maximum kinetic energy of the emitted electrons is independent of the intensity of the incident light.
2. The existence of a threshold frequency below which no photoelectrons are emitted: In classical physics, electrons should be emitted from a metal surface with any frequency of incident light. However, in the photoelectric effect, there is a threshold frequency below which no photoelectrons are emitted.