In
atomic physics
Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. Atomic physics typically refers to the study of atomic structure and the interaction between atoms. It is primarily concerned wit ...
, the Bohr magneton (symbol ) is a
physical constant
A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time. It is contrasted with a mathematical constant, ...
and the natural unit for expressing the
magnetic moment of an
electron caused by its
orbital
Orbital may refer to:
Sciences Chemistry and physics
* Atomic orbital
* Molecular orbital
* Hybrid orbital Astronomy and space flight
* Orbit
** Earth orbit
Medicine and physiology
* Orbit (anatomy), also known as the ''orbital bone''
* Orbito ...
or
spin
Spin or spinning most often refers to:
* Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning
* Spin, the rotation of an object around a central axis
* Spin (propaganda), an intentionally b ...
angular momentum.
The Bohr magneton, in
SI units
The International System of Units, known by the international abbreviation SI in all languages and sometimes Pleonasm#Acronyms and initialisms, pleonastically as the SI system, is the modern form of the metric system and the world's most wid ...
is defined as
And in
Gaussian CGS units:
where
* is the
elementary charge
The elementary charge, usually denoted by is the electric charge carried by a single proton or, equivalently, the magnitude of the negative electric charge carried by a single electron, which has charge −1 . This elementary charge is a fundame ...
,
* is the
reduced Planck constant,
* is the
electron rest mass,
* is the
speed of light.
History
The idea of elementary magnets is due to
Walther Ritz (1907) and
Pierre Weiss. Already before the
Rutherford model of atomic structure, several theorists commented that the magneton should involve the
Planck constant ''h''.
By postulating that the ratio of electron
kinetic energy to orbital
frequency should be equal to ''h'',
Richard Gans computed a value that was twice as large as the Bohr magneton in September 1911.
At the
First Solvay Conference in November that year,
Paul Langevin obtained a
. Langevin assumed that the attractive force was inversely proportional to distance to the power
and specifically
The
Romanian physicist Ștefan Procopiu
Ștefan Procopiu (; January 19, 1890 – August 22, 1972) was a Romanian physicist and a titular member of the Romanian Academy.
Biography
Procopiu was born in 1890 in Bârlad, Romania. His father, Emanoil Procopiu, was employed at the Bâr ...
had obtained the expression for the magnetic moment of the electron in 1911.
The value is sometimes referred to as the "Bohr–Procopiu magneton" in Romanian scientific literature. The
Weiss magneton was experimentally derived in 1911 as a unit of
magnetic moment equal to
joules per
tesla, which is about 20% of the Bohr magneton.
In the summer of 1913, the values for the natural units of atomic angular momentum and magnetic moment were obtained by the Danish physicist
Niels Bohr as a consequence of
his atom model.
In 1920,
Wolfgang Pauli gave the Bohr magneton its name in an article where he contrasted it with the magneton of the experimentalists which he called the
Weiss magneton.
Theory
A magnetic moment of an electron in an atom is composed of two components. First, a moving electric charge of the electron forms a current, hence the orbital motion of an electron around a nucleus generates a magnetic moment by
Ampère's circuital law. Second, the inherent rotation, or spin, of the electron has a
spin magnetic moment.
In the
Bohr model of the atom, for an electron that is in the orbit of lowest energy, its
orbital angular momentum has magnitude equal to the
reduced Planck constant, denoted ''ħ''. The Bohr magneton is the magnitude of the magnetic dipole moment of an electron orbiting an atom with this angular momentum.
The spin angular momentum of an electron is ''ħ'', but the intrinsic
electron magnetic moment caused by its spin is also approximately one Bohr magneton, which results in the electron spin
''g''-factor, a factor relating spin angular momentum to corresponding magnetic moment of a particle, being approximately two.
See also
*
Anomalous magnetic moment
*
Electron magnetic moment
*
Bohr radius
*
Nuclear magneton
*
Parson magneton
*
Physical constant
A physical constant, sometimes fundamental physical constant or universal constant, is a physical quantity that is generally believed to be both universal in nature and have constant value in time. It is contrasted with a mathematical constant, ...
*
Zeeman effect
References
{{Reflist
Atomic physics
Niels Bohr
Physical constants
Quantum magnetism
Magnetic moment