We are often taught as children that there are three states of matter: solid, liquid, and gas. A fourth state exists, that of plasma, which is typically introduced to students in middle or high school. It is effectively a high-temperature gas that’s shedding electrons; it qualifies as a different state of matter because it operates under different properties than a standard gas.
It’s something that most of us can discuss but will never directly experience. That is, unless we have a microwave oven and some grapes.
If you cut a grape almost in half, leaving some skin intact as a hinge, and then put the grape into a microwave and turn it on, plasma arcs are generated above the grape.
It’s a trick that’s been known for years, but as presented in this video, a group of physicists have finally and conclusively explained why it happens.
As noted by Livescience, it comes down to the size of an average grape and its mostly-water composition. The reasoning behind it, though, is that microwaves travel at different speeds through different mediums.
That’s why the speed of light is always given as “in a vacuum”, by the way. The speed of light is actually a touch slower through physical mediums like air, water and glass.
So, while the microwave frequency is comparatively long through the air in the microwave, its wavelength in a mostly-water thing is… about the size of a grape.
The microwaves start bouncing against each other, and form a single very hot spot at the exact point where two grape-length objects touch… like, for example, two grape halves joined by a bunch of skin.
At that point, the superheated grape begins to burn and some of its component elements, specifically sodium and potassium, flare off into plasma.
It’s really cool to watch. There are only a couple of problems. First, you have to be comfortable with the notion of spontaneously generating small bursts of flame in your microwave. Second, you’ll have to deal with the smell of burnt grapes for a while.
But if you’re so inclined, the pretty science might be worth it.
Question of the night: What’s your favorite thing to microwave?
