Plasma (physics)
The fourth state of matter, comprising most of the universe.
Plasma is a state of matter that results from one of the other three classical states (often, the gaseous one) having undergone an appreciable degree of ionization. It consists of a significant portion of charged particles (ions and/or electrons). While rarely encountered on Earth, it is estimated that 99.9% of all ordinary matter in the universe is plasma, including stars and the rarefied intracluster and intergalactic media. Plasma is called the fourth state of matter after solid, liquid, and gas, and is typically an electrically quasineutral medium of unbound positive and negative particles.
- field
- Physics
- known_for
- Fourth state of matter; ionized gas with collective behavior governed by electromagnetic fields
- etymology
- From Greek word for 'result of forming or moulding'; analogy with blood plasma
Lore & Background
Plasma science derives from Irving Langmuir's work in the 1920s, but the issues and initial understanding derive from the history of electricity.
Reader's Guide
Plasma is distinct from the other states of matter. Unlike the phase transitions between the three other classical states, the transition to plasma is not well defined and is a matter of interpretation and context. The presence of charged particles makes plasma electrically conductive, with dynamics governed by collective electromagnetic fields and sensitive to externally applied fields. This response is used in many modern devices and technologies, such as plasma televisions or plasma etching. Plasma can be artificially generated by heating a neutral gas or subjecting it to a strong electromagnetic field. Depending on physical conditions, a certain number of neutral particles may also be present, in which case plasma is called partially ionized; examples include neon signs and lightning. Ideal plasmas are defined by three factors: the plasma approximation, bulk interactions, and collisionlessness. Non-neutral plasmas have a significant excess of charge density, while dusty plasmas contain tiny charged particles of dust.
Did You Know?
- It is estimated that 99.9% of all ordinary matter in the universe is plasma.
- Plasma is typically an electrically quasineutral medium of unbound positive and negative particles.
More in Thermodynamics And Statistical Mechanics 1-22
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