The fourth state
Plasma is known as the fourth state of matter and is in fact the most common state of matter. Over 99% of the matter in the universe is plasma. It is in the form of an excited gas. Plasma is created when the gas gets so hot that the electrons are stripped away from the atoms, giving it a positive charge.
Examples of Plasma
One common example of a plasma is the flame of a candle. The candle wax burns and gives off a hot gas that emits energy, in the form of light. It is this excited and hot flame that is known as plasma. All fire is plasma. The light we see during a lightning strike is plasma. Another example of plasma is the sun and other stars. The light and heat of the sun is a result of hydrogen and other elements in a plasma state.
Uses of Plasma
Argon gas in a plasma state interacting with the phosphor coating within a glass tube gives us fluorescent lighting. Neon signs use argon in a plasma state interacting with mercury and phosphorus to produce their bright colors. Another example is the plasma television which works by applying electricity to cells of xenon, neon, and helium gas between two plates of glass. When the electricity is applied to the cells the gasses become plasma and interact with different phosphors to form the colors we see on the screen.
Gas laser systems, for example Helium/Neon types, use the two inert gases in a hot and excited state to emit large bursts of light energy.
Some specialised welding apparatus use a plasma of inert gas to prevent the metals from oxidising (by excluding oxygen from the surrounding air) while being welded.