WEBVTT - How Do Microwave Ovens Work?

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<v Speaker 1>Welcome to brain stuff from how stuff works. Hey, brain stuff.

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<v Speaker 1>This is Christian Sager. There is no denying it. Microwave

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<v Speaker 1>ovens are super convenient. They can heat food much more

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<v Speaker 1>quickly than a conventional oven, although not always with the

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<v Speaker 1>same results. And there's an entire industry of food made

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<v Speaker 1>specifically for these nifty gadgets. But how do they work? Yeah,

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<v Speaker 1>of course you're saying right now, well microwaves. Sure, yeah, microwaves.

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<v Speaker 1>But what the heck are microwaves? Good question, Christian. Microwaves

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<v Speaker 1>are a type of wave on the electro magnetic spectrum,

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<v Speaker 1>and their sandwiched between radio waves and infrared radiation. In

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<v Speaker 1>the case of microwave ovens, the most common wave frequency

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<v Speaker 1>is roughly two thousand, four hundred and fifty mega hurts.

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<v Speaker 1>That's about two point four or five giga hurts. Waves

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<v Speaker 1>in this frequency range have an interesting property. They're absorbed

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<v Speaker 1>by water, fats, and sugars, and once absorbed, they're converted

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<v Speaker 1>directly into atomic motion, which we like to use as heat.

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<v Speaker 1>These waves have another convenient property. They're not absorbed by

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<v Speaker 1>most plastics, glass, or ceramics. Metal, however, does reflect microwaves,

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<v Speaker 1>which is why it's a bad idea to leave a

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<v Speaker 1>spoon and you cheese dip when the oven's on. It's

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<v Speaker 1>also why the devices have metal walls for reflection. You'll

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<v Speaker 1>often hear people say microwave ovens cook from the inside out, right,

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<v Speaker 1>that's the key to the speed. Think about it like this.

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<v Speaker 1>Let's say you're baking a cake in a conventional oven.

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<v Speaker 1>Normally you would bake it at three and fifty degrees

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<v Speaker 1>fahrenheit or a hundred and seventy seven degrees celsius. But

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<v Speaker 1>this time you accidentally set the oven at six hundred

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<v Speaker 1>degrees fahrenheit. The outside of the cake will burn before

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<v Speaker 1>the inside even gets warm, and you'll have ruined somebody's birthday.

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<v Speaker 1>In a conventional oven, the heat has to grate by

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<v Speaker 1>conduction from the outside of the food toward the middle. Hot,

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<v Speaker 1>dry air on the outside evaporates moisture, so the outside

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<v Speaker 1>can be crispy and brown like the crust unbread while

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<v Speaker 1>the inside is moist In microwave cooking, the radio waves

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<v Speaker 1>penetrate the food and excite water and fat molecules more

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<v Speaker 1>or less evenly throughout. No heat has to migrate toward

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<v Speaker 1>the interior by conduction. There's heat everywhere all at once

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<v Speaker 1>because the molecules are all excited together. There are limits

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<v Speaker 1>to this, though. Microwaves penetrate unevenly in thick pieces of food.

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<v Speaker 1>They don't make it all the way to the middle,

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<v Speaker 1>and there are also hot spots that are caused by

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<v Speaker 1>wave interference. But you get the idea. The heating process

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<v Speaker 1>is different because you are exciting atoms rather than conducting heat.

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<v Speaker 1>Inside a microwave oven, the air is at room temperature,

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<v Speaker 1>so there's no way to form a crust. That's why

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<v Speaker 1>microwaveable pastries or hot pockets sometimes come with a little

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<v Speaker 1>sleeve made out of foil and cardboard. The sleeve reacts

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<v Speaker 1>to microwave energy by becoming very hot. This exterior heat

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<v Speaker 1>lets the crust become crispy, as it would in a

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<v Speaker 1>conventional oven. Check out the brainstuff channel on YouTube, and

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<v Speaker 1>for more on this and thousands of other topics, visit

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<v Speaker 1>how stuff works dot com.