The four laws of photoelectric emission:

1. The velocity of electrons emitted is independent of the intensity of light and depends only upon the frequency (or wavelength) of the incident light.
2. Photoelectric current (or the number of photoelectrons ejected per second) is proportional to the intensity of incident light.
3. For a given metal, there exists a certain minimum frequency below which the emission of electrons stops completely. This frequency is called the threshold frequency.
4. Photoelectric emission is an instantaneous process. So, there is no time logging between the incident of light and the emission of electrons.