CHAPTER VII
Ncsf¡1
In emphasizing the fact that there are many unsolved problems,
the remarkable achievement of the quantum theory should not be
forgotten. In the course of but a few years, the new outlook has
enabled an extensive series of apparently disconnected phenomena
MAGNETISM
^ed ion
those ¡ni(
were mins
to be correlated and interpreted, and as a result of the clear con
ception which has been obtained of the essential significance of atomic
magnetism, the special study of the magnetic properties of atoms
will be able to contribute more and more towards the solution of
the problems of atomic structure generally.
E. C. Stoner, Magnetism and Atomic Structure, 1926
Mstmaj
oiitoitle»
Dry apiqrj’
wave.
1. Diamagnetism
IAMAGNETISM is a property common to all matter, and
on the classical theory is regarded as due to a Larmor
precession of electronic orbits, similar to that which is account
able for the Zeeman effect. On this may be superimposed a
larger paramagnetic effect due to change in the orientation of
unbalanced electronic orbits. A considerable amount of experi
mental work has been carried out by Pascal, who has investigated
the influence of chemical combination on the magnetic properties.
It is found that diamagnetic atoms combine to give diamagnetic
molecules, and the effects are approximately additive.
Langevin has given a theoretical discussion of diamagnetism
and shown how an expression for the diamagnetic susceptibility
may be obtained.
The diamagnetic susceptibility may be calculated by finding
the changes in the nature of the orbits produced by the magnetic
field. For simplicity we suppose that the electron orbits are
circular and that their planes are perpendicular to the inducing
field. When v, the number of revolutions per second, is very
great, the circling electron may be regarded as equivalent to an
electric current of strength ve. The magnetic moment of the
equivalent magnet will be veA, where A is the area of the orbit.
For a circular orbit of radius r the magnetic moment
M = venr 2
= \er 2 oo
where a> is the angular velocity of the electron.
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