Published: 29 January, 2004

A phase called plasma: It's a physical state of matter

Why is plasma classified as a phase? What is its chemical make-up? How was it discovered?

Before we answer this question in any detail, we need to understand what matter is made up of. Everything is made up of small particles (pieces) called atoms. These atoms in turn consist of smaller particles. An atom is made up of a heavy positively charged center called a nucleus surrounded by a cloud of much lighter negatively charged particles called electrons. Remember that in nature, positive and negative charges attract each other so they like to stick together, in other words, there is a strong force of attraction between electrons and nuclei. Another point to remember is that atoms also have forces of attraction between them. We will address this point next.

We know that matter can exist in solid, liquid or gas phases. The difference between these phases is that their physical state is different in each case. In a solid, the atoms are very close together, since the forces between the atoms are very strong and hold the atoms tightly together. Therefore a solid is rigid. By heating the solid, we can melt it to form a liquid. In a liquid the atoms are vibrating with weaker forces between them. If we heat the liquid sufficiently, we get a gas. In a gas, the atoms are moving randomly at very high speeds and have very weak forces between them.

Now, what would happen if we keep on heating the gas to an extremely high temperature? Well, what happens is that we get a plasma, which is the fourth phase of matter (at a very high temperature). By heating the gas a lot, we can reach a high temperature, where we supply so much energy to the atoms that the electrons inside the atoms get torn away from the atom and we get electrons and positive ions (the nuclei) floating about in almost equal concentrations. This new phase, in which the atoms have broken up into positive ions and electrons, which move around energetically is called a plasma. The reason a plasma is classified as a phase is due to the fact that a plasma is a new physical state of matter. The keyword to note is physical, because things only move from one phase to another by some physical means - for example, when we supply energy to them, i.e. heat them. In a plasma we have broken up the gas atoms into ions and electrons thus creating a new phase.

In 1929, the term "plasma" was first used by Irving Langmuir, who observed the breakdown of atoms into electrons and ions when high currents were sent through thin wires (filaments, basically light bulbs). He later went on to win the Nobel Prize in Chemistry in 1932. Another scientist, Hannes Alfvén, won the Nobel Prize in Physics in 1970 for his work in plasmas.

An example of a plasma that we can see in our everyday lives is the substance inside a fluorescent light bulb (or tube light). Also, the bright color that you see in neon signs often on display outside shops is also a plasma. It should be noted that 99% of natural matter in the universe is in the plasma state. However, it may seem like we live in the 1% of the universe in which plasmas do not occur naturally. Studying plasmas is very important and plasmas have numerous applications ranging from nuclear fusion research to using them in the high tech electronics industry.