On Food and Cooking

by microwaves. But the oven air, composed of
nonpolar nitrogen, oxygen, and hydrogen
molecules, and nonpolar container materials
like glass, stoneware, and plastic (made of
hydrocarbon chains), are unaffected by the
microwaves; the food heats them as it heats
up.
Here’s how a microwave oven works. A
transmitter, very much like a radio
transmitter, sets up an electromagnetic field
in the oven which reverses its polarity some 2
or 5 billion times every second. (It operates at
a frequency of either 915 or 2,450 million
cycles per second, compared to wall socket
currents at 60 cycles, and FM radio signals at
some 100 million cycles per second.) Polar
water molecules in the food are pulled by the
field to orient themselves with it, but because
the field is constantly changing, the molecules
oscillate back and forth with it. The water
transmits this motion to neighboring
molecules by knocking into them, and the