Microwave takes double the time as conventional

Mattman: How come when I put two potatoes in my microwave it takes twice as long to cook them as to cook one? When I put two potatoes in my conventional oven, it doesn’t take twice as long to bake. I know that microwaves irradiate the potatoes, but exactly how do they do it? Why does it take longer for more food? — Paradigm, the Net

Think of that electronic cooking box as a big field of beams. The wave generator, the magnetron, cranks out tiny (micro-) waves. They travel in a straight line and pinball around inside the box (and off any hard or bony things) until they hit something cookable and penetrate its outer layer by an inch or so. Heat’s generated when the beams’ rapidly reversing electromagnetic field sets the water and any other polar molecules in the taters to oscillating. When you have a whole batch of spuds in the box, they shield one another from the rays, so some get more, some get less, and it takes longer for everything to cook to the same degree of doneness. Put enough grub in there and it will probably take as long to cook as it would in a standard oven. If you insist on ruining a bunch of perfectly good Idahos in a microwave, put them in a circle rather than bunched together. It won’t help a lot, but nuked food is pretty lame anyway, so the longer you postpone eating it, the better off you are.