How Do Microwave Ovens Work? : Short Wave Introducing Micro Waves: low-calorie episodes featuring bite-sized science, mail from our listeners, and...maybe other stuff in the future? We'll figure it out.

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Micro Wave: The Science Of Microwave Ovens + Listener Mail

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Micro Wave: The Science Of Microwave Ovens + Listener Mail

Micro Wave: The Science Of Microwave Ovens + Listener Mail

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  • <iframe src="https://www.npr.org/player/embed/891565434/892081528" width="100%" height="290" frameborder="0" scrolling="no" title="NPR embedded audio player">
  • Transcript

(SOUNDBITE OF MICROWAVE DOOR CLOSING, BEEPING, WHIRRING)

MADDIE SOFIA, HOST:

Maddie Sofia here with our trusty SHORT WAVE reporter Emily Kwong. 'Sup, Kwong-song (ph)?

EMILY KWONG, BYLINE: Hey, Sofia.

SOFIA: Are you excited, ma'am?

KWONG: Aren't I always, ma'am?

SOFIA: (Laughter) So today we are introducing a new occasional type of episode we are calling a Micro Wave.

KWONG: Each Micro Wave, we will explain a little science nugget - just a tiny little brain snack - and then maybe read some listener mail, too.

SOFIA: Today's inaugural Micro Wave topic is microwave ovens. And yeah, we know that isn't super creative. But this is a daily show, y'all, and we're tired.

KWONG: And we're stuck inside, inspired by what's most around us. So after the break, we'll tell you a bunch of stuff about the science behind your favorite kitchen appliance.

(SOUNDBITE OF MICROWAVE DOOR CLOSING, BEEPING, WHIRRING)

SOFIA: Honestly, I don't really think we needed the sound again. You know?

KWONG: I don't know. It sounds like dinner to me.

(LAUGHTER)

SOFIA: OK, Kwong - so how often do you use your microwave?

KWONG: Oh, I'm sorry. I can't hear you. I'm heating up a burrito. What do you want?

SOFIA: How often would you say you think about how it actually works?

KWONG: Actually never. Why are you asking (laughter) me this question?

SOFIA: Listen, there's no shame. Not a lot of people think about how their microwaves actually work. But...

KWONG: No.

SOFIA: ...You know who does?

KWONG: Who?

SOFIA: Ramaswamy Anantheswaran.

RAMASWAMY ANANTHESWARAN: I'm a food scientist and a food engineer.

SOFIA: Ramaswamy works at Penn State University. He's a big-time food engineer. And honestly, Kwong, I felt a little weird calling him just to ask him how a microwave works.

KWONG: It's not the weirdest thing you've ever done.

SOFIA: It's a little weird. But there was nothing to fear, as he is a man after my science communication heart.

ANANTHESWARAN: In addition to doing teaching and research, our outreach responsibility is connecting with the public. So helping people like you is part of our mission.

KWONG: I love that.

SOFIA: I know. Me, too.

OK. Let's get to it.

ANANTHESWARAN: So basically, this mechanism of heating is different than conventional heating. Conventional heating...

SOFIA: So microwave ovens work by shooting energy in the form of waves called microwaves at your food. And those waves are made by a tube in the oven called a magnetron.

(LAUGHTER)

KWONG: One of the most underappreciated Transformers - never got any screen time in the movies.

SOFIA: Truly - you hadn't even heard of him until today.

KWONG: (Laughter).

SOFIA: But microwaves are used for, like, all types of technologies. We use them to send information via communication devices all the time.

ANANTHESWARAN: That energy is the same energy used by your cellphones but a higher power.

SOFIA: Wow. So these waves essentially create, inside your little microwave, an electromagnetic field. Ramaswamy says microwaves interact really well with molecules that are positively charged on one side and negatively charged on another. Those are called polar molecules.

KWONG: So sort of like those bar magnets we used to play with in high school with one...

SOFIA: What do you mean used to? You know what I'm saying?

KWONG: (Laughter).

SOFIA: Are you done playing with bar magnets?

KWONG: I have other things to do in my free time.

SOFIA: Wow. Wow, wow, wow - fancy pants. Too fancy for magnetism but fine.

KWONG: OK. So bottom line - the molecules are polarized like magnets basically.

SOFIA: Yeah, basically.

ANANTHESWARAN: And the most dominant polar molecule in food is water.

KWONG: So most of the way microwaves work is by messing with the water molecules in our food?

SOFIA: So this is how it goes down. The microwaves oscillate, which means the current inside the oven kind of alternates back and forth.

ANANTHESWARAN: When it alternates, the charge shifts from left to right. And as a result, the water molecule starts to rotate clockwise and anticlockwise millions of times.

SOFIA: And that superfast flipping of the water molecules back and forth creates friction between the molecules. And friction, of course...

KWONG: Creates heat....

SOFIA: You got it, Kwong. OK.

KWONG: It's like a little molecule dance floor.

SOFIA: That's right (laughter). So each vibrating - dancing water molecule acts as, like, this little localized heater throughout the food.

KWONG: OK. But my most pressing microwave question is, why does food stay cold in the middle? - 'cause it's not like water molecules are only on the outside of food. You know?

SOFIA: Yeah. Right. No. So of course it depends on the makeup of the food you're heating. And one thing that contributes to uneven heating is the presence of salt. So you know, like, super salty foods like soup don't actually heat as evenly as foods that have barely any salt in them. Like, I'm sure you've noticed that when you're out there souping. Right?

KWONG: Oh, sure. Sure, all the time.

SOFIA: OK. So that's partially because these little salt ions on the surface or along the sides of the bowl absorb a lot of that initial microwave energy and heat up really fast. But that means that there's not kind of enough energy left over to penetrate all the way into the middle. That's why when you look at the microwave and you're like - what's up, soup? - and you look in there and you see, like, the surface is boiling and then you dip your little spoon in there and it's all a lie - soup still cold.

KWONG: It happens. So what are you supposed to do about that?

SOFIA: Yeah. Well, it's pretty complicated. You just stir it.

KWONG: Oh, jeez.

SOFIA: You just stir the soup halfway through, Kwong. That's it.

KWONG: OK. We got it.

SOFIA: (Laughter) But really, Ramaswamy says besides, you know, like, safety, that's actually why a lot of foods suggest that you let the food sit in the microwave for a minute after it's done, which helps that heat kind of even out a bit.

KWONG: Oh, wait. Most important question from my childhood - is it safe if I look directly into the microwave as I wait for my burrito to be done?

SOFIA: You absolutely may look in the microwave, Kwong, as long as your little microwave isn't broken and has passed all its little, like, microwave baby check-ups and it's all perfectly safe. I mean, in Ramaswamy's words...

ANANTHESWARAN: The only danger is if the microwave dropped on your foot.

(LAUGHTER)

KWONG: I love food scientists.

SOFIA: Oh, I know. I know.

KWONG: OK.

Before we go each Micro Wave will also share some listener mail.

SOFIA: Yes. You can write us at shortwave@npr.org. A couple of weeks back, Craig (ph) wrote us. Subject line - appreciation from the desert...

KWONG: (Reading) Hi, Maddie. I really enjoy your podcast, and it helps me start each day while I make coffee on my tailgate. I think this fact has served as additional positive reinforcement because I tend to associate your daily episodes with my daily dose of caffeine, and I'd be a fan either way.

SOFIA: I'm fine with that.

KWONG: (Reading) I'm a field biologist working primarily with desert tortoises and the common ravens who prey on them in the Mojave Desert. We work mostly in the middle of nowhere by ourselves, so we are kind of always in some state of social isolation. However, this season has been particularly difficult, not being able to see co-workers or my family, and your podcast has really meant a lot to me.

SOFIA: I love that. That's really nice.

KWONG: (Reading) P.S. - Here are a couple pictures of a little tortoise who refused to leave the shade of my tire the other day. He was kind of grumpy when I explained to him I needed to drive away.

Craig sounds really nice.

SOFIA: I mean, aren't we all a grumpy little tortoise under a tire right now, Kwong? You know?

KWONG: And don't we all need a little Craig to be nice to us?

SOFIA: Oh, I agree. OK. All right. So here's one more that we'll read that I really love. This is about our recent episode on helium where we played with some balloons and, yeah, I bit into one and sucked the helium out because I'm a human being.

And it reads, hi, I enjoyed the helium episode until the very end. Teeth should be used for smiling and eating, not as tools to pop a balloon, et cetera. Teeth...

Wait, wait, wait - this is the best part.

KWONG: (Laughter).

SOFIA: Teeth are jewels, not tools, signed Brenda Berkal (ph), DMD - aka a dentist.

KWONG: A dentist. This is because you called your teeth nature's scissors, isn't it?

SOFIA: I said what I said, Brenda.

KWONG: OK. Well, we appreciate you, Brenda. And everyone, this has been our first-ever Micro Wave episode. If you have a question for us or suggestions for a future Micro Wave, email us at shortwave@npr.org.

SOFIA: This episode was produced by Brent Baughman, edited by Viet Le and fact-checked by the tortoise under Craig's tire.

(LAUGHTER)

SOFIA: JK - it was checked by Yowei Shaw. Thanks, Yowei.

I'm Maddie Sofia.

KWONG: And I'm Emily Kwong. Thanks for listening to SHORT WAVE from NPR.

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