That mysterious and useful little box in your kitchen — the microwave — is a marvel of modern science and engineering. How does something so complicated help you heat up leftover pizza with the touch of a button?
Microwave ovens work by emitting electromagnetic radiation. This is the very same radiation that produces light and radio signals, with the difference being that microwaves are a wavelength of 12.2 cm and oscillate at a specific frequency of 2.45 gigahertz (GHz). In a microwave oven, this radiation is generated by a small and somewhat complicated device called a magnetron. Briefly, a magnetron works by causing a spinning vortex (like a hurricane, or whirlpool) of negatively charged particles called electrons, that when moving within the magnetron, create a continuously changing electric field — these are the microwaves.
Many molecules that are present within food (especially water) interact with the electric field such that they try to align themselves with it, and when this happens, the molecules move very rapidly back and forth to try to keep in sync with the changing microwaves. The moving molecules bump into other nearby molecules and make them move as well.As more and more molecules start moving faster and faster, the substance (say, your leftover mashed potatoes) starts to heat up. This is why frozen food takes much longer to heat up in a microwave oven because many of the molecules are frozen in place so they cannot move as easily back and forth.
Did you know? Raytheon, an American military contractor working on radar systems, made the first commercial microwave ovens.
Unlike conventional heating, using an oven that relies on the movement of hot air to heat your food from the surface to the inside, microwaves can actually penetrate into the food leading to it being more evenly heated.Although the food does get cooked on the inside, microwave ovens do not heat food from the inside out, contrary to popular belief.
Did you know? The inner walls of a microwave oven are made of metal that reflects the microwaves, keeping them contained in the appliance.
You've probably heard that putting metal in a microwave isn't such a great idea. There's two reasons for this. First of all, since metal actually reflects microwaves, any metal that is put in microwave (like tinfoil around your food) would reflect the microwaves and keep them from cooking the food. Secondly, there's a chance that the metal can build up an electric charge, caused by the electric field of the microwaves. If enough charge builds up, it can cause “arcing” with electrical discharge and sparking. Though not necessarily dangerous, arcing can damage the microwave oven.
HowStuffWorks "How Microwaves Work"
Suite 101.com: Why no metal in microwaves
An explanation of how magnetrons work
Seeing where the microwaves are in a microwave oven
Article first published March 18, 2011.