Plasma is one of the four fundamental states of
matter, the others being solid, liquid, and gas. A plasma has properties unlike
those of the other states.
A plasma
can be created by heating a gas or subjecting it to a strong electromagnetic
field applied with a laser or microwave generator. This decreases or increases
the number of electrons, creating positive or negative charged particles called
ions, and is accompanied by the dissociation of molecular bonds, if present.
The
presence of a significant number of charge carriers makes plasma electrically
conductive so that it responds strongly to electromagnetic fields. Like gas,
plasma does not have a definite shape or a definite volume unless enclosed in a
container. Unlike gas, under the influence of a magnetic field, it may form
structures such as filaments, beams and double layers.
Plasma
is the most abundant form of ordinary matter in the Universe, most of which is
in the rarefied intergalactic regions, particularly the intracluster medium,
and in stars, including the Sun. A common form of plasmas on Earth is seen in
neon signs.
Lightning
is an example of plasma present at Earth's surface. Typically, lightning
discharges 30,000 amperes at up to 100 million volts, and emits light, radio
waves, X-rays and even gamma rays.[13] Plasma temperatures in lightning can
approach 28,000 K (28,000 °C; 50,000 °F) and electron densities may exceed 1024
m−3.
Much of
the understanding of plasmas has come from the pursuit of controlled nuclear
fusion and fusion power, for which plasma physics provides the scientific
basis.
