is: the phenomenon whereby electrons are ejected from metals which are illuminated by electromagnetic radiation of suitable frequency (usually ultraviolet radiation). [P10.1]
occurs: when each ejected electron completely absorbs the energy of a single photon.
cannot be explained: by the classical wave model of electromagnetic radiation. [P10.1]
was explained: by Albert Einstein (1879-1955) (see Einstein's photoelectric equation) by assuming that the interaction energy of electromagnetic radiation occurs in discrete quanta, given by the Planck-Einstein formula:
where 
is Planck's constant and 
is the frequency of the electromagnetic radiation. [P10.1]
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