Definition of Plasma

What is a Plasma?

Plasmas are one of the four common states of matter - the others are solids, liquids, and gases.

In general, but not in all specific cases, as the temperature increases and pressure decreases substances pass through the four different states.

solid → liquid → gas → plasma

Almost all the observable matter in the universe exists in the plasma state.

The Plasma State

The plasma state of matter is characterized by the following:

  • charge separation by ionization: a plasma is a gas whose atoms have lost some or all of their electrons - it is a gas of ions and electrons
  • a plasma has no definite shape or volume
  • plasmas are overall electrically neutral, containing balanced numbers of positive and negative charges.
  • plasmas are electric conductors, whereas gases are insulators
  • plasmas form at very high temperatures: the higher the temperature and the lighter the element, the more fully ionized the plasma's atoms are likely to be:
    • the solar corona and the interior of the sun are fully ionized plasmas
    • lightning strikes consist of partially ionized plasmas, as do electric sparks
    • lights based on ionized noble gases, such as neon lights, contain partially ionized plasma
    • at lower temperatures, plasma may contain un-ionized neutral species, whose proportion falls as the temperature rises
  • average speeds of particles in plasmas are higher than in gases, with a higher proportion of atomic- and molecular-sized particles moving at very high speeds

The image below is a neon light. A high voltage is applied to neon at low pressure, ionizing it to produce a plasma.

neon light plasma

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