Speed of Light in a Microwave (with marshmallows!)

In your senior science studies, you may have learned about Hertz and his experiments with what we now recognise as radio waves. Through a series of experiments, he was able to demonstrate that the mystery radiation he was creating with the sparks from an induction coil behaved not only as a wave, by demonstrating that it showed the wave behaviours of reflection, diffraction, refraction and interference, but also that it was a transverse wave, demonstrated by the fact it could be polarised, just like Maxwell’s predicted electromagnetic radiation.

Many of Hertz’s experiments relied on his being able to use the reflection and interference properties of the mystery waves to create standing waves.

States of Matter: Plasma

At some point during your science studies, you would have been introduced to the idea of The Three States of Matter: solid, liquid, and gas. As you may have realised when thinking about, for example, the melting of glass, or contemplating the nature of a flame, this three state model doesn’t tell the whole story. Solid, liquid, and gas are more like three categories into which more specific states of matter fit. This series explores some of these states which perhaps don’t seem to fit neatly into the three states model as you may have learned it.

Plasma. No, we’re not talking about the watery part of blood. Plasma is often called “the fourth state of matter” because it’s what you get when you keep putting energy into a gas. (Recall: in the three states description of matter, solid + enough energy = liquid, liquid + enough energy = gas.) A plasma is a lot like a gas, but where a gas is made of uncharged atoms or molecules, (referred to as “neutrals” in plasma science, for obvious reasons), in a plasma some proportion of those neutrals have shed some of their electrons to become ions. The electrons are free and also form part of the plasma. So, a plasma is made of a mix of neutrals, ions, and electrons, in an equilibrium, in any proportion.