Everything about Spin Physics totally explained
In
physics and chemistry,
spin has a special meaning, representing a non-classical kind of
angular momentum intrinsic to a body, as opposed to
orbital angular momentum, which is the motion of its
center of mass about an external point. Although this special property is only explained in the
relativistic quantum mechanics of
Paul Dirac, it plays a most-important role already in
non-relativistic quantum mechanics, for example, it essentially determines the structure of atoms.
In
classical mechanics, any
spin angular momentum of a body is associated with self rotation, for example, the
rotation of the body around its own center of mass. For example, the
spin of the
Earth is associated with its daily rotation about the
polar axis. On the other hand, the
orbital angular momentum of the Earth is associated with its
annual motion around the
Sun.
In fact, in classical theories there's no analogue to the quantum mechanical property meant by the name
spin. The concept of this nonclassical property of elementary particles was first proposed in 1925 by
Ralph Kronig,
George Uhlenbeck, and
Samuel Goudsmit; but the name related to the phenomenon of
spin in physics is definitely
Wolfgang Pauli.
Spin in quantum mechanics
In
quantum mechanics, spin is an intrinsic property of all
elementary particles related to
angular momentum.
Spin obeys
commutation relations analogous to those of the
orbital angular momentum:
» :
). This implies that our original measurement of the spin along the x-axis is no longer valid, since the spin along the x-axis will now be measured to have either eigenvalue with equal probability.
Direct and indirect applications
Well established
direct applications of spin are
nuclear magnetic resonance spectroscopy in chemistry;
electron spin resonance spectroscopy in chemistry and physics; proton spin density with
magnetic resonance imaging (
MRI) in medicine; and
GMR drive head technology in modern
hard disks.
A possible application of spin is as a binary information carrier in
spin transistors. Electronics based on spin transistors is called
spintronics.
But finally we remind to the many
indirect applications based on spin and the Pauli principle, for example the
periodic table of
Dmitri Mendeleev.
Further Information
Get more info on 'Spin Physics'.
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