The observed behavior in which light falling on certain metals can eject electrons from the surface.
Frequency dependence
It can be shown experimentally that the maximum energy with which electrons are ejected varies in direct, linear proportion to frequency of the light falling on the metal (that is inversely with the wavelength).
Intensity dependence
It can be shown experimentally that for a fixed wavelength the rate with which electrons are ejected varies in direct linear proportion to the intensity of the light.
