Microwave ovens cook things by shooting radio waves at food, right? So if I put something small in the microwave, and it doesn’t catch many… microwaves, are the other microwaves wasted, or do they play some other role?

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Microwave ovens cook things by shooting radio waves at food, right? So if I put something small in the microwave, and it doesn’t catch many… microwaves, are the other microwaves wasted, or do they play some other role?

In: Physics
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Microwaves bounce around the interior very quickly so your item has a lot of opportunities to “catch” those waves. But some proportion of them are instead going to be absorbed by things like the walls of the microwave or the magnetron itself. Heating up the magnetron is usually considered to be a waste so those waves are not useful.

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Microwave ovens create what are called standing waves. Basically they’re pockets of high energy areas throughout your microwave, and the fact that they’re called “standing” means they aren’t moving, or are moving slowly, which is why there’s a turntable in most modern microwaves. As the table turns, it moves your food through the pockets of high energy where the water in your food absorbs some of it, heating it up. Surrounding the entire cooking area is a thing called a Faraday cage, which is shunted to ground. This gives the excess/unused energy a place to go (to ground). So yes, the energy not being absorbed by your food is wasted.