What is plasma?

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Most people have been taught that there are three common states of matter: solid, liquid, and gas.  However, there is a fourth state of matter called plasma. But exactly what is plasma and how is it made?

What is plasma?

Plasma is made by adding a large amount of energy to a neutral gas so that some of its electrons split from their atoms. The plasma remains electrically neutral but contains unbound electrons and positively charged ions.

Plasma is usually quite hot, as it takes large amounts of energy to break the electrons away from their atoms. At lower temperatures, the electrons and ionized atoms come back together into whole atoms and the plasma turns back into a neutral gas. Plasma in which most of the particles have been ionized is termed “hot” plasma, while “cold” plasma has only a small fraction of its particles ionized. However, cold plasma is still several thousands of degrees Celsius in temperature.

While gases behave in predictable ways, plasma behaviour is quite different. Gas particles all respond to gravity and collisions with each other. But in plasma the particles all have different charges, masses, and temperatures, so they all exhibit different behaviour, independently of one another.

In addition, the particles in plasma aren’t dense enough to create many particle collisions, so magnetic and electrostatic interactions become very important. Charged particles moving in a magnetic field creates an electric current, so the movement of particles in plasma both influence, and are influenced by, the movement of the other particles (and the fields they produce).

This also affects how the plasma behaves. Because of the charged nature of plasma, it is a better conductor than copper, and can be contained using magnetic fields.

Plasma is commonly found on Earth both in man-made forms (neon and fluorescent lights, plasma screens) and natural forms (lightning, the Northern and Southern lights). The Northern and Southern lights are created when the solar wind, which is a jet of charged particles, hits Earth’s magnetic field.

Because the particles are charged, they follow Earth’s magnetic field lines, and then collide with atoms in the air over the North and South poles. This excites the atoms in the air, and the oxygen and nitrogen in the air gives off light.

In space, stars are mostly made of plasma under high pressure, and the spaces between planets in our solar system, between stars in our galaxy, as well as between galaxies are likely filled with low-density plasma.