Measuring Planck’s Constant
By
Martin Hackworth
Historical Perspective and Physics Theory
Max Planck (1858-1947) was born in Kiel Germany and attended schools
in Munich and Berlin. Planck was an early pioneer in the field of quantum
physics. Around 1900 Planck developed the concept of a fundamental unit of
energy, a quantum, to explain the spectral distribution of blackbody radiation.
This idea of a basic quantum of energy is fundamental to quantum mechanics of
modern physics. Planck received a Nobel Prize for his work in the early
development of quantum mechanics in 1918. Interestingly, Planck himself
remained skeptical of practical applications for quantum theory for many years.
In order to explain blackbody radiation, Planck proposed that atoms
absorb and emit radiation in discrete quantities given by
hfEn
=
where:
• n is an integer known as a quantum number
• f is the frequency of vibration of the molecule, and
• h is a constant, Planck's constant.
Planck named these discrete units of energy quanta. The smallest discrete amount
of energy radiated or absorbed by a system results from a change in state
whereby the quantum number, n, of the system changes by one.
In 1905 Albert Einstein (1879-1955) published a paper in which he used
Planck's quantization of energy principle to explain the photoelectric effect. The
photoelectric effect involves the emission of electrons from certain materials
when exposed to light and could not be explained by classical models. For this
work Einstein received the Nobel Prize in Physics in 1921.
Niels Bohr (1885-1962) used Planck’s ideas on quantization of energy as a
starting point in developing the modern theory for the hydrogen atom. Robert
Millikan made the first measurement of Planck’s constant in 1916. The best
current value for Planck's constant is 6.62607554 x 10-34 J · s.
