Rights: © Copyright 2014. University of Waikato. All Rights Reserved. Published 29 April 2014 Download

The classical states of matter are solid, liquid and gas. In this video clip, Associate Professor Bob Lloyd from the Physics Department, University of Otago, explains how gas can be converted into a highly charged and energetic state of matter called plasma. Plasma is the fourth state of matter.


A gas is where you have molecules or atoms separated, moving around in free space. Forces between them are fairly low, so that’s why they can move around. And a  plasma is when they get a little bit more energy and the electrons are removed from some of the atoms and so they become what’s called ionised, so they have a charge. So a plasma is where the gas exists as a collection of electrons and atoms which are positively charged.

A plasma looks identical to a gas. At room temperatures, you can’t tell the difference unless you’ve got an instrument which will tell you whether the particles are charged or not. As you heat the plasma up, it starts to act a bit differently like an ionised gas, and if you heat it up enough, it acts a little bit like the Sun.

If you heat a gas up sufficiently hot enough then the electrons will have enough energy to escape individual atoms. If you apply radio frequencies or bombard them with other particles, you can also strip the electrons of atoms and produce a plasma.

Solid, liquid, gas and plasma – so plasma is often called the fourth state of matter

Associate Professor Bob Lloyd, University of Otago, Department of Physics

Holster Engineering Ltd, Tokoroa