may be written:
where 
is Planck's constant. [P10.1, P10.2]
relates: the energy 
of a single photon to the frequency 
of monochromatic light composed of such photons. [P10.1]
is also known: as Planck's law, Planck's formula or (in a more specific context) the Planck-Einstein formula. [P10.1]
Copyright 1997, The Open University