A law that is the basis of quantum theory, which states that the energy of electromagnetic radiation is confined to indivisible packets (quanta), each of which has an energy equal to the product of the Planck constant and the frequency of the radiation
(physics) the basis of quantum theory; the energy of electromagnetic waves is contained in indivisible quanta that have to be radiated or absorbed as a whole; the magnitude is proportional to frequency where the constant of proportionality is give by Planck's constant