Why I don’t do fun science tricks with microwave ovens

Posted on by Matthew Wright

It occurred to me the other day that one dandy way to clean a microwave oven is to chuck a cake of soap into it and blast it on ‘high’ for a few minutes.

Artwork by Plognark http://www.plognark.com/ Creative Commons license
Artwork by Plognark http://www.plognark.com/ Creative Commons license

It was a better idea than my previous microwave-inspired trick which involved dismantling the rotating platter and using egg whites and a ruler to measure the speed of light in air.

Sound nuts? Actually, it’s a physics principle. Let me explain. A microwave oven only heats things when the wave is at maximum amplitude, so the platter spins so the food is evenly heated.

If you remove the rotating platter, you defeat that part of the design. Now add a flat plate spread with egg white and turn the machine on. The cooked parts appear as stripes. You then measure the peak-to-peak distance  with a ruler, which gives you the wavelength.

The thing is, if you know the frequency and the wavelength, you can calculate the velocity at which the wave propagates – and, conveniently, the operating frequency is usually written on the manufacturers’ tag at the back of the microwave. The magnetron emits electromagnetic radiation at lightspeed (light IS electromagnetic radiation) – so voila, you can calculate the speed of light in air armed with nothing more than a ruler, egg-white, a plate, and a microwave oven.

This trick also works with custard.

Why didn’t I do it? For obvious reasons it’s better not to do it with the main household microwave, so I had to wait until we replaced it. Then I never got around to setting up the old one for the experiment before we finally decided to throw it out.

But what about the soap idea? In case you’re wondering, microwaved cake soap foams. As in, if you have enough soap it fills the appliance and then starts spewing out every possible gap in the casing. Technically, it’s being boiled.

See? Clean. Sort of. A bit.

And also in case you’re wondering, no I didn’t actually do it – I’m sure my wife wouldn’t stop me, but I’d have to mop it up. Then I’d have to go and buy another microwave because, hey, who wants soap perfume all through the microwave forever?

Which probably means you shouldn’t do it either.

Copyright © Matthew Wright 2016

22 thoughts on “Why I don’t do fun science tricks with microwave ovens”

  1. Sounds like this is a good one to leave to Youtube enthusiasts. Although, there is one good way to clean a microwave. Half water, half white vinegar (roughly 1.5 to 2 cups) in a bowl, microwave five-ish minutes. Wipe down the inside. Easiest microwave clean ever.

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  5. Apparently, the reason water boils (aside from heat) is because of impurities. If water is absolutely pure it won’t boil. The Mythbuster guys tried this out and microwaved pure water. It didn’t boil as theorized. Then they stuck a fork in it…and the water exploded! Great stuff.

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    1. Must check that one out – I didn’t see that episode. I’ve had problems with reheating coffee that isn’t apparently boiling, but which erupts as soon as it’s moved. Probably a similar principle I guess.

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    1. Because the microwave is built as a Faraday cage which traps the radiation. That’s why the door has a metal grill inside the glass. The holes are smaller than the wavelength of the radiation. I gather there are rules about the scale of allowed leakage. It’s why a microwave shouldn’t be used with a broken or warped door.

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    1. No problem providing he didn’t turn it on for (say) 1 minute on ‘high’. Oops, did I mention that I want to set up a golf ball manufacturing company alongside my microwave repair business…😅

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