Max Planck
1858 - 1947
PLANCK'S-LAW
Wien identified the temperature-depended
displacement of the peak in the emission spectrum
of a glowing solid in 1893. The formula for the total
emission spectrum of a photon has only been
deduced in 1901 by Max Planck. He discovered that
the wave- and radiation characteristics of a photon
depends on the energy transition of the related
electron according the relation: E = hf. In this
formula, which is called Planck's law, E is the
amount of expelled energy in Joule, f is the
frequency of the emitted (electromagnetic) radiation
in Hertz and h equals 6,626 x 10^-34 Joule-second
(Js), being Planck's constant. In daily life it is quite
easy to imagine the unit Joule. 1 Joule corresponds
with 1 Watt during 1 second so in one minute a
40-Watt incandescent lamp converts 40Wx60s =
2400 Joule of energy into heat and light. In relation
to individual electrons however, the unit Joule turns
out to be unmanageable large and therefore often
the unit electron Volt (eV) is used instead. One eV is the amount of energy that is
required to make an electron overcome a potential difference of one volt. When using
electron Volts, the relation E = hf remains unchanged but E is now expressed in eV
instead of Joule and since one electron Volt corresponds with 1,602 x 10^-19 Joule,
h is transformed to 4,136 x 10^-15 electron Volt-seconde (eVs). An energy transition
of 1,24 eV then results in an electromagnetic radiation with a frequency of f = E/h =
1,24 eV/(4,136 x 10^-15) eVs or about 300.000 GHz. The wavelength of this radiation
follows from the equation λ = c/f in which λ is the wavelength in meters, f
the frequency in Hertz (Hz) or vibrations per second and c is the speed of light, about
300.000 km/s. 300.000 GHz then turns out to be infrared radiation (IR-A) with a
wavelength of λ = c/f = 1000nm.
