What is Plasma State of Matter | Fourth state of Matter

Definition of Plasma, Plasma Production, Applications, Plasma is a form of matter in which many electrons move freely between the nuclei of atoms.

▶Definition of Plasma

Plasma is a form of matter in which many electrons move freely between the nuclei of atoms. Plasma is called the fourth state of matter, the other three being solids, liquids, and gases. The basic difference between solids, liquids, and gases is in the difference between bond strengths.

The word plasma comes from the Greek and means something molded. In 1929, it was first applied by Tonks and Langmuir, to describe a remote, internal field from the boundaries of a glowing ionized gas produced by an electric discharge in a tube. Ionized gas is an entire remaining electrically neutral gas.

Long range of electrostatic forces in a plasma
Long range of electrostatic forces in a plasma

Plasma is superheated matter – so hot that the electrons are ripped away from the atoms forming an ionized gas. In the night sky, plasma glows in the form of stars, nebulas, and even the auroras that sometimes ripple above the north and south poles.

Generally, electrons in solid, liquid, or gaseous samples of matter reside with similar atomic nuclei. Some electrons can move from atom to atom if an electric current flows in a solid or liquid, but the motion is in the form of small jumps by individual electrons between adjacent nuclei. In plasma, a significant number of electrons have such high energy levels that no nucleus can capture them.

An atom that has lost some of its electrons, thereby obtaining an electric charge, is an ion. When a gas is taken to heat or an electric field, some of its atoms become ions, and the gas is said to be ionized. An ionized gas, unlike a gas in its general state, can conduct electric current to a limited extent. If the heat or electric field becomes extreme, many atoms become ions. The resulting super-ionized gas is a plasma, which can conduct a large and continuous electric current.

By heating a solid or a fluid, atoms or molecules acquire more thermal kinetic energy until they are able to exceed the binding potential energy. This causes a phase transition, which occurs at a constant temperature for a given pressure. The amount of energy required for a phase transition is called latent heat.

▶Plasma Production

By increasing the temperature of a substance a plasma can be produced until a very high partial ionization is achieved. Under thermodynamic equilibrium conditions, the degree of ionization and electron temperature are closely related. Plasma can also be generated by ionization processes that raise the degree of ionization far above its thermal equilibrium value.


Applications of plasma are included in electric lamps, Controlled Thermonuclear fusion, lasers, medical devices, energy converters, water purifiers and flat-panel video displays. About 99% of the visible universe is made up of plasma.


Plasma consists of free electrons and ions that aren't associated with atomic nuclei. A plasma occurs when a gas is extremely heated or subjected to a strong magnetic field. Here are 10 examples of forms of plasma:

  1. Lightning
  2. Aurorae
  3. The excited low-pressure gas inside neon signs and fluorescent lights
  4. Solar wind
  5. Welding arcs
  6. The Earth's ionosphere
  7. Stars (including the Sun)
  8. The tail of a comet
  9. Interstellar gas clouds
  10. A fireball of a nuclear explosion

▶Read also

  1. Debye shielding in Plasma Physics
  2. Techniques of Plasma Confinement
  3. Relation between Phase velocity & Group velocity

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