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Electron
Electron
The electron is a subatomic
particle. It has a negative
electric charge of -1.6 × 10-19
coulombs, and a mass of about
9.10 × 10-31 kg (0.51 MeV/c2).
The electron is commonly represented as e-.
The
antiparticle of the electron is the
positron, which is identical to an electron but has positive electrical
charge.
Atoms
consist of a
nucleus of
protons and
neutrons surrounded by electrons. Electrons are very light compared to the
other two types of particles: a proton is about 1800 times as heavy as an
electron.
The electron is one of a class of subatomic particles called
leptons which are believed to be
fundamental particles (that is, they cannot be broken down into smaller
constituent parts). The electron has
spin 1/2, which implies it is a
fermion, i.e., follows the
Fermi-Dirac statistics.
The electron had been posited by
G. Johnstone Stoney, as a unit of charge in electrochemistry, but Thompson
realised that it was also a
subatomic particle.
The electron was
discovered by
J.J. Thomson in
1897
at the
Cavendish Laboratory at
Cambridge University, while studying "cathode
rays." Influenced by the work of
James Clerk Maxwell, and the discovery of the
X-ray, he deduced that
cathode rays existed and were negatively charged "particles", which
he called "corpuscles".
The electron is described in
quantum mechanics by the
Dirac Equation.
In the
Standard Model it forms a doublet in SU(2) with the
electron neutrino, as they interact through the
weak interaction. The electron has two more massive partners, with the same
charge but different masses: the
muon
and the
tau.
When electrons move, free of the nuclei of atoms, and there
is a net flow, this flow is called
electricity, or an
electric current. This might be compared to a flock of sheep moving north
together, while the shepherds do not. Electric charge can be directly measured
with an
electrometer. Electric current can be directly measured with a
galvanometer.
So-called "static electricity" is not a flow of electrons at
all. More correctly called a "static charge", it refers to a body that has more
or fewer electrons than are required to balance the positive charge of the
nuclei. When there is an excess of electrons, the object is said to be
"negatively charged". When there are fewer electrons than
protons, the object is said to be "positively charged". When the number of
electrons and the number of protons are equal, the object is said to be
electrically "neutral".
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