Hot, dry air on the outside of the food evaporates moisture, so the outside can be crispy and brown for example, bread forms a crust while the inside is moist. In microwave cooking, the radio waves penetrate the food and excite water and fat molecules pretty much evenly throughout the food. No heat has to migrate toward the interior by conduction. There's heat everywhere all at once because the molecules are all excited together. There are limits, of course. Microwaves penetrate unevenly in thick pieces of food they don't make it all the way to the middle , and there are also "hot spots" caused by wave interference, but you get the idea.
The whole heating process is different because you are "exciting atoms" rather than "conducting heat. In a microwave oven, the air in the oven is at room temperature, so there's no way to form a crust.
That is why microwavable pastries sometimes come with a little sleeve made out of foil and cardboard. You put the food in the sleeve and then microwave it. This increased voltage is needed to power the magnetron, causing a filament to heat up at the core of the device.
As this filament heats up, electrons are released. The microwave oven puts these electrons to work. A circular magnet is located near the heated filament. Normally, the electrons that are released by the filament would become attracted to the anode, but because of the positioning of the magnet, the electrons loop back to the filament itself. This looping of electrons is what actually creates microwaves. All of that may have sounded a little bit complex, and it can be when explained without diagrams.
For a deeper dive into the understanding of how magnetrons and, ultimately, microwaves work, take a look at the video below. One popular myth about microwaves is that they can give you cancer. This may stem from the use of the word 'radiation' in describing how they work, as well as a fear that this microwave radiation can leak out of the microwave.
Radiation, in this case, refers to energy that radiates from a source, and not to radioactivity. However, microwaves do not contain enough energy to chemically change substances through ionization - they are an example of non-ionizing radiation. Other types of electromagnetic waves such as ultraviolet and x-rays possess more energy per photon and thus can cause cancer.
Microwaves can, of course, cause heating and burns, but microwave ovens are all designed with a metal mesh on the door of the appliance to keep the microwaves from leaking out.
These metal meshes are large enough for you to see your food cooking, but the holes aren't large enough for the microwaves to slip through. Microwave ovens also have built-in safety devices that do not allow the oven to work while the door is open.
So, at the end of the day, you won't get cancer from standing too close to a microwave because the rays aren't ionizing, and you won't get cooked either. So, we've gotten through the basic science, but we still haven't covered why exactly microwaves work so well to heat food quickly.
The microwaves used in a microwave oven are sent out through a type of antenna that channels them into the cooking area of the appliance. The waves are contained inside of the appliance thanks to the solid metal walls and mesh door. Chad Mueller, assistant professor of chemistry at Birmingham-Southern College in Alabama, replies: "A microwave oven cooks food because the water molecules inside it absorb the microwave radiation and thereby heat up and heat the surrounding food.
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