Planck's constant, denoted , is a fundamental constant in physics. The current value of Planck's constant is Joule-seconds (numbers in brackets represent uncertainty in the last two decimal places).
It was first used by Max Planck around 1900 to explain the radiation curves of black-bodies. He supposed that light could be modelled as a series of particles (now called photons), each with an energy proportional to its frequnecy, . The constant of proportionality was Planck's constant. Mathematically this can be expressed as:
Reduced Planck's Constant
Planck's constant often occurs in equations with the mathematical constant . As such, a factor of may be taken into Planck's constant as
The resulting constant is pronounced "h-bar".