We go through our daily lives encountering three of the states of matter; solid, liquid, and gas; nearly every moment, but the fourth, plasma, is much rarer for most of us. Plasma can be found around most forms of visible electricity, like lightning, but you can find it inside your microwave if you follow the steps below. Before you get started, however, this experiment MUST be carried out with immense care and with an adult present; it is very easy to get this experiment wrong and deal damage to not only your microwave, but yourself as well.
For this experiment, you’ll need a microwave, a toothpick, a microwave-safe glass container, three discs of cork (or any material you can stick a toothpick into and use to prop up the glass, and a match. Place the four discs of cork in the microwave so that one is in the center and the other three are around it far enough for the glass container can rest on top of them. This is essential, as air needs to flow between the inside of the glass container and the inside of the microwave. Stick the toothpick into the center cork disc, and set the microwave to 20 seconds, but don’t run it yet.
Light the toothpick and cover with the glass container, closing the door of the microwave and hitting start. You should see arcs of plasma coming from the lit toothpick and while it’s tempting to leave it go and watch for a while, only let it run for a few seconds. Otherwise, the glass will get too hot and could shatter, spreading broken glass through your microwave and removing the housing for the plasma, potentially lighting your microwave on fire. After you’ve shut off your microwave, let it sit closed for about a minute, allowing the glass to cool down, otherwise the sudden inrush of cool air from the outside could shatter the still hot glass.
Those plasma arcs were cool, but how exactly did we make them? Well, plasma is essentially ionized gas, requiring either an increase in heat or adding more electromagnetic force, both of which are happening inside the microwave. When an object is burned, the fire is actually stripping away electrons, ionizing the atoms around the fire until the electrons get recaptured. Microwaves work by establishing a standing wave of electromagnetic fields, which push and pull the electrons stripped away from the fire. This causes them to collide with the air molecules inside the glass, adding heat to the air and stripping away more electrons. This continues until the air is ionized to the point of becoming plasma, dissipating, and then ionizing into plasma again. The reason we can actually see the plasma also comes down to those electrons, as their collisions with the air molecules can add energy to the air’s electrons, which then fall back into their normal energy levels and release light, similar to the effect of fluorescence we’ve mentioned in previous pieces.
If you want to make plasma yourself, get an adult and try it, but please remember to be careful.