When light or electromagnetic radiation falls on a metal surface, electrons are emitted from it. The process of emission of electrons from a metallic surface by the incidence of light (photons) is known as photoelectric effect. The emitted electrons are called photoelectrons. The picture below illustrates the photoelectric effect.
Some important terms:
Threshold frequency (fo): The minimum frequency below which photoelectric emission is not possible is known as threshold frequency. The value of threshold frequency is different for different metals.
hfo = ϕ [Where h=Planck’s constant]
or, fo =ϕ/h
Threshold wavelength (λo): The maximum wavelength of light which can eject photoelectrons from a surface is called threshold wavelength. It is the wavelength corresponding to threshold frequency.
λo = c/fo[Where c =velocity of light]
Work function (ϕ): The minimum energy required to eject an electron from the surface is called threshold energy or work function. It is denoted by ϕ and measured in eV. Its value depends on the nature of metal, its purity and the condition of the surface.