Far be it from us to deride anyone’s childish fascination with blowing stuff up in a microwave—a foolhardy nerd rite of passage if ever there was one—and what better place to exhibit dangerous, potentially expensive shenanigans than YouTube? The experiment is simple. Take a seedless grape and slice it lengthwise, making sure (this part is important) not to cut all the way through, so you leave a little bit of skin connecting the two halves. Put it face-up in a microwave, and blam: fireworks!
So what the heck is going on in there? Grapes are chock-full of electrolyte, an ion-rich liquid (a.k.a. “grape juice”) that conducts electricity. Each grape-half serves as a reservoir of electrolyte, connected together by a thin, weakly conducting path (the skin). Microwaves cause the stray ions in the grape to travel back and forth very quickly between the two halves. As they do this, the current dumps excess energy into the skin bridge, which heats up to a high temperature and eventually bursts into flame. At this point, the traveling electrons arc through the flame and across the gap, ionizing the air to a plasma (which itself can conduct electricity) and creating the bright flashes you see.
And that notion about poisonous gas tainting your roommate’s Hot Pocket? Well, the guy’s talking about the ozone generated when the air inside the glass is ionized. “Poisonous” might be too a strong word in this scenario (a little ozone definitely won’t kill you), although high concentrations of ozone can oxidize lung tissue and have been known to cause asthma in urban inversion-bowls like L.A. and Mexico City.
Again, DON’T TRY THIS AT HOME. Microwave ovens + biological capacitors = bad news. —Martha Harbison.
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