How Do Microwaves Cook Food?
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Microwave ovens cook food incredibly fast, warming up refrigerated leftovers in minutes or less. But how does this great invention work?
Here, we explore the science behind one of the most revolutionary household appliances of the 20th century.
Microwaves Are A Form Of Energy
Microwaves are electromagnetic waves that fly through space at the speed of light. We can't see microwaves, but if you could, you would see the microwave cooking chamber light up with an intense glow.
Microwaves are shorter than radio waves but longer than infrared radiation. The microwave used for cooking is about 12 centimeters from crest to crest, says Louis Bloomfield, a professor of physics at the University of Virginia. At this wavelength, microwaves are readily absorbed by most foods. But the particles in a microwave, known as photons, don't have enough energy to damage molecules and cause cancer like ultraviolet rays or X-rays.
The Microwave Oven
A component called the magnetron generates microwaves from electricity inside the microwave oven. To power the magnetron, a transformer converts the standard household electricity from a wall socket of 120 volts to about 4,000 volts or higher. The voltage heats a filament at the center of the magnetron, boiling off electrons.
Most microwaves have a glass turntable that moves the food around like a carousel so that it heats evenly. If the food wasn't being rotated, parts of your meal would get stuck in the microwave's hot and cold spots.
How Microwaves Cook Food
When you hit the start button "it usually takes about 2 seconds to heat up a filament inside the magnetron tube," says Schiffmann. The microwaves are then blasted into the food compartment.
Microwaves heat food, like a cup of coffee or a slice of lasagna, by twisting water molecules back and forth. Water molecules are positively charged at one end and negatively charged at the other. A single water molecule looks like Mickey Mouse's head, says Bloomfield. You can think of the negatively charged oxygen atom as Mickey's face and the two smaller positively charged hydrogen atoms as Mickey's ears.
The positively charged end of the water molecule tries to align itself with the microwave's electric field while the negatively charged end points the other way. But because the field reverses 2.5 billion times a second, Mickey's ears and face are being twisted back and forth rapidly.
As the molecules twist back and forth, they rub into each other. This creates friction, which produces heat.
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