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Berg: Wozzek (Opera in Berlin) | Discovery of the Ionosphere | First
Leica-camera Electric | The Roaring `20's: Charleston |
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Pauli's Principle |
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Pauli's principle, also known as Pauli's exclusion principle, was
proposed by Wolfgang Pauli in 1925. The starting point was the problem of the
completion of atomic shells and the structure of the periodic system of the
chemical elements.
On the basis of the multiplet structure of the atomic
spectra and the anomalous Zeeman effect, which was not able to be interpreted
for a long time, Pauli realized that the peculiar, classically non-describable
type of ambiguity of the quantum theoretical properties of the luminous
electron demands for its description a fourth quantum number. So he added a
spin quantum number, as it was later known, to the three known quantum numbers,
principal quantum number, orbital quantum number and magnetic quantum
number. |
According to this postulate, two electrons in an atomic
structure can never have all four quantum numbers in common. If one electron in
an atom assumes a state described by all four quantum numbers, then this state
is occupied.
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For a long time, the exclusion principle remained an
unexplained supplement to quantum theory. But Pauli never gave up his goal of
connecting his principle to other physical principles. It took almost another
15 years of dealing with the problem until he found the final explanation.
It turned out that the exclusion principle applies to particles with
half-integral spin, e.g. electrons and protons. If these particles are
described quantum statistically, then the so-called Fermi-Dirac statistics are
employed. Such particles are known as fermions. On the other hand, particles
with integral spin, e.g. photons, do not obey the exclusion principle and
follow Bose-Einstein statistics. Such particles are known as bosons. |
| In 1945 Wolfgang Pauli was awarded the
Nobelpreis
for his discovery of the exclusion principle. |
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