Let's Talk Physics

A stochasticly updated blog about interesting topics in Physics & Astronomy

Plasma – the state that really matters

Most people are taught in primary school that there are 3 fundamental states of matter – solid, liquid and gas. Sadly, and as usual with any branch of science taught to a 12 year old, this is a lie. There are, in fact, 4 states (this in itself is another lie, but I’ll come to that in a few weeks). The 4th is a very special form of matter – one which ruled the Universe at its beginning, and which is commonly used in modern technology. This 4th state is called a plasma.

A typical everyday plasma – the plasma globe!

So what is a plasma? Well, to understand what it is, first of all, we need to understand how to make a plasma. Imagine you have a solid in your hand. If you heat it up, eventually, the bonds holding the molecules together as a fixed, regular structure will break and the clumps of molecules will slide around each other to form a liquid. Adding some more heat cause all of the bonds holding the clumps of molecules together to break, and a sea of individual molecules will form, making a gas. So what happens when we add even more heat?

Well, molecules are made up of atoms. The atoms are made up of a nucleus, which is made up of protons and neutrons, and then a cloud of electrons that orbit the nucleus. When enough energy is added to a gas, then the electrons can be stripped away from the atoms in the gas, leaving behind the nucleus. So, instead of a sea of molecules, we now have a sea made up of 2 components – the nuclei of the atoms, and the electrons (which are now not bound to the nuclei). Since the nuclei are positively charged (all they are made up of are protons and neutrons) we call them ions. This soup of ions and electrons, where the electrons no longer orbit the nucleus of an atom, but rather fly around on their own, is the fourth state of matter.

The 4 states of matter (Credit: UC Regents)

Plasmas sound very exotic, but we see them in use every day. In fact, plasma is the most common form of matter in the Universe! Plasma is used in plasma screens, neon signs, lights, some forms of medicine. It occurs naturally in lightning and in the interstellar medium. And it’s what stars are made up of!

Electron Density and Temperature for which certain Plasmas occur (Credit: Dr. Tony Herbert)

Electron Density and Temperature for which certain Plasmas occur (Credit: Dr. Tony Herbert)

So why is this important? Well, I’ll get to that in 2 weeks time. As for next week, I’m going to be talking about the Photoelectric effect. Until then!



About irishphysicist

I'm a PhD student with the Departments of Physics in University College Cork, Ireland and University of Notre Dame, Indiana. I want to try and bring astrophysics to the public, and also would like world domination. But that's a story for another day.

2 comments on “Plasma – the state that really matters

  1. Pingback: The Photoelectric Effect | Let's Talk Physics

  2. Pingback: The First Few Minutes | Let's Talk Physics

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This entry was posted on June 10, 2013 by in Astrophysics, Physics and tagged , , , , , , , , .
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