Origins of “hn"        Energy E = hn        Quantum energy of a photon

                                                            n – frequency of radiant energy or light

                                                            h – Planck’s constant = 6.626 x 10^-34 Joule – sec

In 1900 Max Planck tried to explain the relationship between the emitted radiation from an object and the temperature of the object. Planck derived a formula that describes light as having discrete energy states or quantized energy. Planck’s formula describes energy of radiation as proportional to it’s frequency multiplied by a constant, now known as Planck’s constant “h”.

Planck hypothesized that radiant energy could only exist in discrete amounts or quanta which is proportional to the frequency of radiation. It was a revolutionary idea that energy could only come in discrete packets. Planck thought he came up with a fudge factor.

Einstein carried on Planck’s work and proposed that light delivers energy in packets or chunks leading to the conclusion that light consists of small particles which are now referred to as photons. Each photon has an energy equal to Planck’s constant multiplied by its frequency n (pronounced “new” or “nu”).

These concepts were very revolutionary leading the discovery of the Photo-electric effect where free electrons are created by the transfer of energy from photons creating kinetic energy to set electrons in motion. Einstein won the Nobel prize for his work on the photo-electric effect which was made possible by Planck’s formula E=hn.