COLD COOKING

The two household appliances with the highest power consumption are the kitchen range and the clothes drier. (Freezer and refrigerator consume more energy, since they run continually.)

But most of the heat produced by the kitchen range is wasted. The heat creeps with excruciating slowness into the pot, from there into the water, and from there into the egg that is being boiled. Why heat the pot and the water when only the egg needs to be heated?

Heat is the random motion of molecules. At absolute zero, if we could reach it, they would sit still; as the temperature is increased, their vibrations become wilder and wilder. A "hot" or vibrating molecule will bump into a "cold" molecule and kick it into vibrations, too; that is essentially how heat is conducted. The molecules of the pot bump into the molecules of the water, which bump into other water molecules, until they bump into the molecules of the eggshell. The heater keeps the pot molecules vibrating, and the heat transfer continues until the egg is boiled.

That is a stone age process, for there are ways to kick the molecules of the egg without the intervening pot and water. Almost all materials have free electrons, orphans wandering about in the material without being attached to any atom. When the material is struck by an electromagnetic wave, these electrons oscillate in harmony with the impinging wave and bump into the molecules of the material, heating them by kicking them into vibrations.

Some materials (insulators) have very few free electrons, so that the heat caused by an electromagnetic wave is negligible. Others (conductors) are full of them, but they cannot be heated this way, either, because the dense layer of free electrons oscillating on the surface will reflect the wave and will not let it get into the interior of the conductor. The only type of material that can be heated this way is one that lies in-between: Its free electrons are neither abundant nor scarce. It is called a "poor conductor".

Now by a quirk of nature, all foods are poor conductors; and by a quirk of custom, plates and many food containers are insulators (porcelain, plastic, glass, paper). So if a strong electromagnetic wave hits an egg on a plate, it will heat the egg and leave the plate cold. No heat is wasted. Any other food can be heated this way in cold surroundings, which saves a lot of energy (half or more).

Which is exactly what a microwave oven does. And besides energy, it saves time. It takes 1 minute to "boil" a cold egg, dinner can be warmed up in a few minutes right on the plate as it stood in the refrigerator, frozen food can be unfrozen in a few minutes, etc.

The electromagnetic wave is produced by an electronic tube called a magnetron, which produces radiation close to the frequencies of UHF TV stations. The oven is a box lined by metal; the wave bounces around the inside of the box and cannot get out - opening the door turns off the magnetron. The energy is entirely absorbed by heating the food in the oven.

In energy savings per investment cost ($350 or so), let alone in convenience, a microwave oven is hard to beat. It seems destined to become an essential part of the American household.