How does it work?
Perhaps we should start by wrapping our heads around the work mechanism behind our dearly beloved microwave oven. The idea is actually pretty simple. Your microwave is essentially a big magnetron that creates electromagnetic waves at a certain frequency called the microwave range (0,3-300 GHz). Your oven only uses a certain width of that spectrum. Different materials absorb different wavelengths, which enables your microwave to magically heat food, but not the plate it is placed on. Modern microwaves are usually calibrated to heat water, fat and sugar particles. This design characteristic allows for great consumer convenience, but it also this same characteristic which can compromise your health and security.
The most common warning given by manufacturers is not to put anything containing or made of metal in your microwave. But isn't the microwave itself made of metal? It certainly is. So what's going on here? If you look closely at the door of the microwave, you can see it is covered with a metal lattice consisting of a web of holes. Microwaves aren't narrow enough to pass through these, where as the waves of light are. This is why you can see inside, but your head isn't turned into brain soup when held next to a working oven. The metal casing actually creates what is called a Faraday Cage. This helps keep the microwaves contained. However, if you nuke something like a metal spoon or a cup with golden lining you are almost certainly going to see sparks. This is due to the structure of all metals, which lets electrons run free between ions. Subjecting these electrons to high-energy microwave beams will easily over-excite them, thus creating electric arcs, sparks or even explosions. Microwaving metal is also a good way to destroy the magnetron inside your appliance.
Another thing I'd advise you to refrain from doing is using your microwave when empty. Running it empty for too long might fry your magnetron, just like with metal. This is so because microwaves have nothing to be absorbed in and start building up a static charge inside the cage. Something analogous can happen when you try to microwave a piece of food that has been tightly packaged in aluminum foil or other microwave-reflecting material. The energy created by the magnetron has to have an outlet for it to turn into heat. This is why I advise against covering your food with materials that have high reflective properties.
Microwaving eggs, grapes and extremely dry foodstuffs
Some types of food just don't work with the microwave. One of such are eggs. If you try to heat a whole egg, it is bound to explode, because the inside and outside of the egg take different time to heat up - and again - if energy can't escape it will build up until it finds a way out. Eggs can, however, be effectively prepared in a microwave. You only need to scramble them first.
Would you believe me if I told you that microwaving grapes creates a ball of plasma? Well it does. It might be fun to look at (there are a plethora of videos out there, check them out) but it does run a serious risk of damaging the components of your home appliance.
Microwaves need water (or other similar) molecules which to jiggle to slowly heat the food up. If your product is extremely dry, though, the heat generated by molecular resonance can be so great as to actually set the thing on fire.
- dry ice (explodes)
- CDs (plasma and fireworks)
- matches (plasma and ball lightning, will ignite)
- soap (mountain of bubbles that re-solidifies afterwards)
- lightbulbs (extremely toxic mercury and lead fumes)
- Foods high in vitamin B12 (diminishes the concentration by more than a third)