Physics 2000 Einstein's Legacy Microwave Ovens

Tile Analogy

I'm having trouble understanding all this stuff about how waves bounce around in a microwave oven and what the wavelength has to do with it. Don't you have any of your wacky analogies for this one?

Sure! Imagine you're putting tile down on a bathroom floor...


Hang with me for a second here, you're putting this tile down, and when you finish the first row, you find that the tiles fit exactly. So you start going back the other way, and happily discover that the tiles line up perfectly.


Uh, Dr. Hellman...I don't think that's how they put tile down...

It's just a physics analogy, Kyla, not a home improvement tutorial.

OK, you were saying...

Right. But now let's think about what happens if the tiles are just a little smaller. Now there's a little gap left at the end of the first row, so we have to cut a piece from a whole tile to make it fit. Now, if you think of the tiles as light waves, you can't just "throw away" a piece; so we have to use our leftover piece at the beginning of the next row. But by using this shorter piece, we've now thrown the whole row out of line from the first row.


I get it! And when you get to the end of THAT row you find that you have to chop off a little more than before. And on each row you more and more off from the original! If it's even a tiny bit off at first, with enough rows you'll eventually see how far off it is.

Exactly. And the same thing happens when microwaves don't fit evenly inside the oven. After bouncing back and forth a bunch of times they end up so "out of phase" with the first wave that they end up cancelling each other.

So THAT's why any microwaves that don't fit an "integer" number of times in the oven end up cancelling themselves. NOW I get it! Good analogy, Dr. Hellman!

Below is an applet you can play with. Use the buttons to adjust the size of the floor, and see what happens to the layout. The digital counter tells you how many tiles will fit across for the current floor size.

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