It is an observation that many metals emit electrons when light is focused on them
and these electrons are called photoelectrons
ur welcm

This Is a Certified Answer

Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
Hertz performed the photoelectric effect experiment.

Electrons are ejected by metals like potassium, rubidium,caesium when they are exposed to a beam of light. The electrons are ejected from a clean surface of metal.

Photoelectric effect is observed when the frequency of light is more than a threshold frequency. The energy of electrons emitted increases with the frequency of light.

The number of electrons ejected is proportional to the intensity of light.

Einstein explained the effect with the help of Planck's quantum theory.