1. Photoelectric action is an instantaneous event. There is no black delay between the incident of light on the metal surface and the emission of electrons from it. No matter the intensity of the light, as soon as a light ray of suitable frequency is incident on the metal surface, electrons are emitted from the surface and as soon as the light is turned off, the emission of electrons stops. 2. The kinetic energy of photoelectrons depends on the frequency of incident light but not on the intensity of light. 3. Photo current I (Photo current) for any given frequency is proportional to the intensity of the incident light, that is, when the intensity of light increases, the photo flux increases and when the intensity of light decreases, the photo flux decreases. 4. Every metal has a minimum frequency , regardless of the intensity of the incident light, if its frequency does not exceed this minimum frequency then no electrons are emitted from that metal. This is called metal starting frequency , fo .