How Microwave Ovens Work

does on these occasions, is senior writer Jonathan Strickland. And we're coming to you alive, even though a blizzard of epic proportions is going on directly outside the studio of how stuff Works dot com, or at least it's snowing,

and in Atlanta, that's like the snow apocalypse. Yeah, so um as, as the world breaks down outside and we see the angry mobs set fire two cars and raided all the grocery stores for all the milk and bread that they have, eggs and eggs and toilet paper, we will we will soldier on and bring you another fresh, hot, tasty episode of tech Stuff. And in this case, the episode comes to a courtesy of a little listener mail. This listener mail comes from Timas and I hope I'm

saying that correctly. It could also be Timas or some other pronunciation of which I'm unfamiliar, and it goes like this. Hi, I'm Timas from Taiwan. I'm in eighth grade. I just started listening to your podcast and I already love it. I have a quick question for you. How do microwaves work? Please answer it if you have time, preferably in a podcast. Thanks. Keep up the awesome work. Ps. Please reply so I can make sure I have the right email address. Well,

I did reply, so he knows he has alright email address. Uh, we are going to talk about microwave ovens. We're assuming that's what he means by microwaves, because microwaves themselves are a form of electro magnetic radiation. Yes, they are a particular kind that their wavelengths can measure from anywhere from a few centimeters to about a foot long. Uh, that's huge for radio waves. Visible light is actually in the

pnenometer scale four seven hundreds or nanometers. I did it the way you like, specifically, so we wouldn't have to do that, Yeah, which is which is why? Yes? Where Yeah? So either either either either? Yeah? This is ah. This is all thanks to a guy named Percy Spencer. Yes, back in nine, which, Uh, it's kind of a funny story. I actually saw an episode of I can't even remember

what it was. It's one of those those history of mechanics shows, probably something, but anyway, it was talking about different inventions, and the way he discovered microwaves could cook was very very interesting. I mean, he was already working with microwaves, but for radar purposes, because he was working his candy ball. He didn't melt this candy bar. He was working with a radar system, yes, which uses a

device called a magnetron. Yes. He was working on it for the Raytheon Corporation, Yes, and still is involved with a lot of defense stuff. Yes, exactly. Yeah. So during his his experiments, I mean, the magnetrons have been in use for for several years up to that point, he just noticed that when he took it out of its uh of its casing and it was working on it

with some other experiments. He knows one day that the candy bar he had in his pocket had mysteriously melted, and he thought, I wonder if this has anything to do with this magnetron do hickey, Except he probably thought of it in much more scientific terms. He then decided to try and experiment. He placed some kernels of unpopped popcorn next to it. He read that sucker up by pulling the little chain, getting that diesel engine going. Um.

Actually that's not exactly how it worked. But he turned it on and watched as the unpopped popcorn became popped popcorn and said ah ha. And then of course he did the next logical step. He put an egg next to it and watched it explode. It's true, it's totally

I know it was. I know, it's totally true. That's the funny thing is it's just amazing that he didn't immediately like put a grape next to it, and then maybe an incandescent BOWLB But I mean, all the things that you see on YouTube of people putting stupid stuff in the microwave, it's amazing he was the one that was discovering that it was stupid. Perhaps perhaps he was doing it and we just haven't don't have the record of it. And then and then he did a compact disc.

He invented the compact disk. So no, he did not invent the compact disc. No, no, no, But it is kind of funny because you figure if the microwave. The microwave emissions from the Magnatron were cooking the candy bar and the popcorn and the egg. Probably wasn't doing him very much good. But as I used to joke about that, but as it turned out, he lived a very long life,

so well, apparently I didn't do him too much. He would you would feel the effects pretty quickly, because I mean, it does heat up tissue very It's it's not like it just magically goes from from uncooked to cooked. But we'll get into that. We'll talk about the actual sequence that happens when microwaves encounter, um, anything that happens to have some sort of moisture in it. Well, um Percy Spencer. His discovery led Raytheon to release the world's first microwaveve

and in which incredibly compact. Right. Oh yeah, it was the size of a refrigerator five and a half feet tall. So yeah, the first microwave was just a little shorter than my wife. But that sucker was a lot more powerful than the ones that they have out now because that it was it was essentially an industrial microwave machine. It was you know, very very early on and very

very expensive cook an entire deer in just five seconds. Wow. Um, anyway, they were they ran between two thousand and three thousand dollars yea, and the very first one cost about five grand. They're very very the very first one five thousand dollars, which in ninety seven was about the same price as you could get for Poland you are just on a roll today anyway, it's snowing outside. It's a snow day,

right anyhow. Um, so you know, this was a little bit out of the price range of the average American household, right, So Raythoon licensed the technology to t Happen. Uh, and in nineteen fifty five, T Happen introduced the first domestic microwave oven, which was still out of the price range of the average uh, you know household, um, but you know, as considerably cheaper than those giant industrial models. Um. And then uh, Raytheon inquired Amana, so there you go to

the Amanda radar range. The two names came together and uh, you know it's in sixty seven, Raytheon did their first domestic hundred volt microwave oven, which was under five and of course now they're you know, approximately seven dollars if you really wanted to. You could go out buy one ruin it by putting one of the things you're not supposed to put in it, and then watch go out and buy another one, and you're really only out likes. So not that you should put anything uh weird in

your microwave. You shouldn't. You really shouldn't. Don't do it. You could end up burning down the apartment. Besides, it's more fun to watch it on YouTube because then you let somebody else ruin their microwave and you get to keep yours right, and you also get to hear all the hilarious comments that go on in the background. Oh my god, and wow and this is stupid. Yeah, and then you're thinking, and you videotaped it, and not only that, but then went to the next step of uploading it

to the internet to share it with everyone. So microwaves cook. Oh yeah, let's get what they do using a They have a hurts or two point five gigga hurts h frequency. Yes, these are radio waves, remember so, um, let's that's specifically the kind of electromagnetic radiation we're talking about in the radio wave spectrum. And uh, they the thing waves of this this frequency can be absorbed by water and fat

and sugar and some other stuff. Yeah, and uh, when they do get absorbed by these materials, those materials begin to generate a lot of atomic motion, which we also can refer to as heat. So there you go. The material absorbs these these waves, which then makes the material heat up and that can cook a um, well, whatever it is you put in there that happens to have water, bad, sugar or whatever in it. But it also means that certain other kinds of materials do not absorb these microwaves

as metal. Metal metal actually reflects it, which is which is why you don't stick a fork or some aluminum foil in your microwave oven, you know. But you know what, uh, here's here's the thing is that if you do put metal in your microwave, like regular metal, not not like a foil, but something that has got more substance to it, so like a pot or whatever or it can, it's

not necessarily gonna spark um Ith. The sparking comes from things that if you were to have it too close to one of the walls of the microwave, where the differential between the metal that's in the whatever it is that you put in there and the metal of the wall that could possibly create a plasma that would end up sparking. But in most cases, what's really gonna happen is the metal is going to just reflect the microwaves off of whatever it is you're trying to nuke, and

then you're not gonna have a hot dish. It's the food itself is not gonna get is not gonna absorb enough microwaves to heat up properly because the metal has reflected it all. And you know, just to to let you guys know, I mean, yeah, you're not supposed to put metal in the microwave, but it's because it inhibits the food from heating up rather than anything else. It's just like the the screen that's on your microwave door. You know, you look through a microwave and you see

that little grid. It's a mesh. It's that's made out of metal. It's there. It's there to reflect microwaves back into the oven so that they don't go shooting out and nuking everything in your house. Yes, actually that's uh, the mesh is actually uh. I'm glad you mentioned that because I was interested in the mash because I had heard some people talking about why it was mesh and why it was there. You know, it's very important to have that mesh on there. Um. But you may wonder

why it has little holes in it. Well, actually I um um. Funnily enough, I was at how Everything Works dot org, which being not really a competitor of ours actually sort of. Uh. You may know Lou Bloomfield who uh used to be on the Discovery Show. Um some assembly required. Um. He he wrote a piece. He actually answered several questions about microwaves and um. One of those

is why the holes are there in the mash. Now, um, the holes you need the metal reflective surface on the door to keep the microwaves inside the oven and from you know, coming out of there and nuking your head. Should you be checking on the condition of your dinner? Um? Well, you know, and somebody's gonna bring up the fact that we're using the word nuke when it's not actually nuclear, but that it's it's colloquial. We're using nuke in the

colloquial to microwaves something. Yes, but you need that mesh there for one to do that. But you also have to see the condition of your food or whatever. It

is that you put in their coffee popcorn. Um, and uh, the holes are in there and you would think, well, maybe those are gonna let the microwaves out well as uh, as Luke Bloomfield explains, the microwaves are actually at a have a larger wavelength than the holes in the mash, so you can see in, but they can't come back out, which is really cool that it's and they're actually they can, uh, the wavelengths being you know, few centimeters to even feet

in size. That's um, that's pretty cool. It's a lot like the prison I drive by all the time. You can see in, but they can't get out. Okay, So anyway, moving on to talking more about how these microwaves heat up material and cook them because microwaves are absorbed by this whatever material you've put into the microwave itself. Um, not necessarily because the foods that you put in there to be to have them absorbed, right, Yes, yes, that's

what I mean. Specifically, I'm not talking about the plates or whatever, because some of those don't. Yes, okay, So the stuff you put in the microwave to actually heat up, Mr Pellette, the stuff you nuke in the microwave. Okay, anything that anything that has these materials that do absorb microwaves. They do so uniformly right, well, assuming that there's not

too thick. If if the material is too thick, like if you were to put an entire chicken breast, for example, in there, and the chicken breast was a particularly meat each can breast, that might not be the best idea because you might not the microwaves might not be able to penetrate deeply enough to really heat up the chicken breast in a uniform way, and then you could end up with some raw chicken in the middle, and that's

not good. Raw chicken in the middle, And depending on how long you cook it, it could be so you know, crunchy on the outside that you couldn't even eat it. Yeah, it'll be in it rubberized. So a normal oven cooks through uh you know the whole convection conduction thing. Yes, it's where you're conducting heat from one area to another. So you're cooking from the outside in. Heat is being applied to the outside of whatever the food is. That heat slowly moves inside and then eventually you have a

cooked meal. And usually that means the outside is crispier or as as more well done if you prefer, then the middle is has has had heat applied to it for a longer time and uh and in a more direct way. Microwaves accord s don't do this. The material absorbs the microwaves, and microwaves are being bounced all around the the oven so that it's hitting. Ideally, it's hitting the food from pretty much every direction possible at that point,

but of course it doesn't. Each microwave is a little bit different and they changes the age, which is why they have that carousel in the middle to spin the food to try to make sure that everything gets heated. People who use older microwaves often have to stop halfway through and rotate the food and then started again because just because the way the microwaves are are are the microwave ovens are designed, microwaves do tend to hit one

side more frequently than another. I mean, it's because they go through this little microwave trough and then they come into the oven itself. They're not completely randomized, so if you aren't, if you don't have a carousel in your microwave, you may have to turn the food once or twice in order to have it heat evenly. Um and um. Yes, I was going to say the the microwaves are hitting the food and they're heating it up, but the air inside the microwave oven is staying at relatively the same

temperature because the air is not absorbing the microwaves. Um. And this is another something interesting I found by reading our article about microwave and something site um that uh. I always wondered about those little silvery sleeves that you get with certain kinds of food like hot pockets. Yes, not that we're not we're not sponsored by them or anything. It's not. That's a good example. Without them, I would

have died in college. But yes, things that you want crispy on the outside, because things when I was talking about the chicken breast earlier, when I said crispy, it's not We're not talking like the crust on a slice of bread. We're talking rubbery and hard and black in some cases from carbonization. Um. Now this, if you want something like that, like something with a uh that has been fried to be sort of crispy on the outside, you're gonna have to heat up the outside more than

you heat up the the middle and do that. They use this foil. That foil is designed to absorb those microwaves, and it heats up faster than the rest of the food, which heats at the outside of the food in addition to cooking the rest of it, so it makes the outside crispy. It's kind of it's kind of simulating what would happen if you put it in a regular oven. Yes, because it's not an approximation. I mean it is an approximation. It's not the real thing. Yeah, exactly, you can only

kind of sort of fake it. Um and uh, let's let's talk a little bit about what actually is going on here when you when you switch your microwave on. So what's going on here? You plug your microwave in. Now, First of all, microwaves have a switch that um will only remain shut if you close the door, So the microwave will not operate while the door is open, because the circuit is not is not complete until you close the door. It's very important for the safety of everybody

on the outside of the microwave. People inside the microwave, you're kind of screwed. So the door closes, that completes

the circuit. No no. I. Uh, you close the door, You've completed the circuit, and then the electricity from your from the power outlet comes in through the microwave, and uh, it goes through first a regular Uh, it goes through a low voltage UM section of your microwave, which this is what powers everything from like uh, your timer, the circuitry, everything that the fan that will turn as the microwave is going, or the carousel that turns as the microwave

is going, UM, all the low voltage stuff. UH takes that. That's what hits first. After that, it goes into the high voltage transformer and this boosts the voltage significantly because it turns out the magnetron um not the leader of the Decepticons. As I will discovered, you were just talking about transformer. This is true, um, but yeah, that's what confused me. I was like, it goes into a high

voltage transformer and it's called magnetron. Is it a Decepticon? No. Uh. The high voltage transformer then feeds energy into the magnetron, which is what converts the electricity into radio waves known as microwaves. Uh. The microwaves are there's a fan that's blowing and the reason the fan blows is to kind

of break up the microwaves so that they go in. Uh, it randomizes it a little bit so that you don't just have a stream of microwaves hitting a very specific spot on the in the oven, because otherwise you would just have one really hot spot and the rest of it wouldn't be very effective, which would mean you would have to place food in a very specific point in the oven um, which kind of you know, defeats the purpose. So uh, it goes. The microwaves go through essentially a trough. Really,

it's it's a guidance system. They come into the oven, they get randomized a bit, they bounce around until they are absorbed by something um or they just fizzle out, and then then you get your hot, tasty popcorn, which I can't stand because it gives me migraines. Yeah, I'm sorry, but stove cooked popcorn is so much better the microwave popcorn. It just is. Yeah. Oh, and although it is a quick sack, I agree. I should say that the trough I'm talking about, it's it's a metal channel. It's actually

called the wave guide. The name just totally jumped out of my brain. While I was talking about it. But as I looked on in my notes, I realized, hey, I actually did write that down wave guide and so yeah, I'm Steve. Will be your wave guide today. Right on your left you will see the microwaves. Actually you won't because it's outside the range of visible light. Yeah, and uh, if you want to know how magnetron's work, wow, this gets this gets pretty complicated. Yeah, you know, I didn't

into that in my research. So they are made up of an anode, a cathode, a filament, and a couple of magnets and um. The idea here is that you're generating a flow of electrons that go from the cathode to the anode. You use the magnets to alter the path of the electrons so that they spin in a Instead of going in a straight line, they go in a curve, and this curve gets tight and they start spinning.

This is what generates the radio frequencies, the microwaves. And um, it's you know, I've I've read this description three or four times and then I realized, you know what we need to do send an email to stuff from the science lab and have them explain how magnetrons work because I think it's more science than tech at this point. Um, it's actually pretty cool. There's some great illustrations on the web in various places that show you what the anode

and the cathode look like. Um, the anode actually has chambers in it. Uh. And I read the technical description, like I said, three or four times, and I'm still not entirely certain exactly what the mechanics are or you know, the physics are behind this. But yeah, you uh, you pump the high voltage through and uh, you generate the electron flow. The magnets alter the the path of the electrons.

That's what creates the radio frequencies, which will eventually cook whatever it is, you know, your Rama noodles or whatever that you're thrown in there. I've thrown out a lot of brand names. Yeah, you know today, I didn't mean to do that. Well again, I'm thinking, like I don't. I don't use microwave ovens as often as I used to. If I do use microwave oven it's to heat up

something that I cooked in a more conventional method. Um. Mostly because the foods that tend to come design specifically for microwaves also don't tend to be very healthy, and I'm trying to eat healthier now because I want to last a nice long time to to hunt your every waking moment. You know, I've seen green friendly websites talk about using microwave ovens because they use less energy, they are very efficient, um than conventional ovens, so you know

there is an advantage in that. That is true. Um, However, I can't stand what they do to bread. Yeah, well I can eat this for the next two seconds, so I guess we can talk very quickly about some of the stuff that you shouldn't put in a microwave. Um. And honestly, people don't put this stuff in a microwave. Um. If if it doesn't hurt you, it will probably hurt your microwave. Yeah, if nothing else, you may end up damaging your microwave, which is not gonna win you any

points in any household. But damaging yourself is certainly not good either, so please don't. So, for instance, have you seen any videos of someone who's cut a grape almost all the way in half and then microwaved it? Um? You know no, But I actually read a one of those questions by Mr Bloomfield. Um. Actually probably Dr Bloomfield. Um I was talking about blueberries because they were wondering why they're blueberries were catching on fire. He was saying, well,

actually the blueberries are not technically catching on fire. But I'm thinking, I'm thinking, what I think I know what's happening here. So you cut a grape almost in half until it's just being held together by the skin on one side. So you cut them long ways, put them on, say like an upturned coffee mug. You put set the microwave for you know, fifteen seconds or something, and then you'll start to see the grape spark and sometimes you'll see some pretty impressive sparks fly up out of the grape.

Sometimes it might even catch on fire, and you're thinking, what the heck is happening here? Why are grapes doing this? The theory here is that the microwaves hit the grape, which then heat up very the grape. He's very quickly. There's a lot of moisture in that grape which ends up gasifying. It turns into a gas exactly. Well, that's the thing is that first it's a gas, but the microwaves excite the gas, turning it into a plasma. So

a plasma is an ionized gas. It's a gas in which free electrons are roaming around and it is uh, it's it's one of them. It is the most common form of matter in the universe. The sun is plasma. So you're you're technically turning a bit of that grape into plasma. It's it's the evaporation from the grape ends up being excited by the microwaves. That becomes an ionized gas and that's what you see when it sparks. Um and a lot of other materials will do similar things

when you put them into a microwave. That will give off this um, this gas that can get excited by the microwaves. So yeah, don't do grapes um, don't put don't put eggs. Just like an egg in its shell, don't do that. Don't put that in the microwave. It will explode the the internal part of the egg will heat up to the point where the steam generated will be too great for the egg to maintain structural integrity. And then you have a massive mess. Bar of soap

ivory soap, but there's another brand name for you. Put a bar of soap in there, and it ends up turning into a big foamy mess. But fortunately it's easy to clean because it's soap. Um actually might end up cleaning your entire microwave in the process, but I still don't recommend you to do it because you could end up burning yourself very badly. Um. Let's see what other things lightbulbs do. Not put any kind of lightbulb into

a microwave. Yes, the microwaves can heat it up and make it light up in your microwave and it looks neat, but they will explode, which, first of all, that's incredibly dangerous. You're talking about shards of glass flying around. Uh. Second, well, if you're using a fluorescent light bulb, you've got some really nasty chemicals in there, like mercury that can be uh they're very toxic, and you don't want to release that into your environment. Peppers, you don't want the nuke

peppers if you can help. But you know why, why not because they give off plasma, but because they will possibly release some steam that has kept say us in it and then you've just tear gas yourself. Nice ask me how I know this? Oh yeah, and you know our producer of the day, Matt it's also nodding and owning up to Mr Frederick and I apparently both enjoy these spicy foods. And we can tell you by the way nuking dried peppers particularly bad as I discovered. Yeah,

you don't want to do that. If you don't, if you value things like your eyesight and um and the love of those around you, because nothing, there's nothing quite like spraying pepper spray across an entire living area to really, um, you put a strain on relationships. You know. One other thing you don't want to do is overheat stuff you like, like a like a type of water superheating, yes, like quid And people think this is some kind of a myth.

How how could water explode on you? Well, the thing is if you make a liquid too hot past the point at which it's going to boil, and if the container it's in is so smooth that there are no nuclayic sites there for the water to actually boil. Yeah, I mean something generally, a liquid that boils needs something to boil on, like a pebble or something to introduce some some kind of irregular surface for it to start

boiling on. If you uh, you know, NUCA cup of coffee and then decided to put sugar in it, you may suddenly have boiling coffee. What you've just done is you have introduced a nuclaic site into a superheated liquid, and then it's going to boil spontaneously, which looks a lot like an explosion um and can severely burn you.

It can happen now most of the time. For this to happen, like I said, you need to have used some sort of very smooth vessel to hold the liquid because otherwise it's going to find nuclayic sites find not like find in a intelligent way. This is it's gonna latch onto any nuclei, excite and boil within the within

the microwave itself. But if if it's like a very smooth ceramic mug and then you put some like non dairy creamer in it or some sugar something, it'll it'll use as a nucleay e site and just boil immediately. And sometimes just moving the cup will do it. Yeah, because then you know the liquid is now moving and it's it's incredibly dangerous. So yeah, you do need to be careful with that. A lot of microwaves now come with settings that are preset for certain things, including things

like reheating a cup of coffee. Um, and this is stuff that the manufacturer has determined to be within the safe zone. So even then you should still be careful. But um yeah, good point. Glad you brought that up. Thank you. Well, do you have anything else to say about that? Now? I find myself excited by microwaves too, so it was it's pretty cool. Oh well, you know, it ended up being an interesting subject. I'm actually I originally had a one way to wrap this up, but

I'm gonna change it up. I'm so just like just warning you, Pullette. Our listeners have no clue what I'm talking about. But we're gonna end with a little listener mail. This listener mail comes from Matt from Marietta, Georgia, so right up the street. Hey, hey, Matt, I hope you've got enough bread and milk and toilet paper because I don't know if you know this, but it's snowing outside. Matt, says Chris and Jonathan, thank you very much for the

informative podcast. I'm a new listener and have been trying to catch up on your previous episodes. I enjoyed your November eleven, two thou nine podcasts and was hoping to get a little more exposure to some of the topics discussed. First, could you explain a little about plasma generators while not cold fusion? You're back to the future reference made me

think of trash consuming technology. Also, as of yet, time travel is not possible, and I'm gonna cut the rest of Matt's email because we're probably gonna use these for future episodes. Time travel is also probably something from stuff in the science lab, but he wanted to know about plasma generators and UH and trash. I actually wrote an article about plasma waiste converters a long time ago. It's one of my first articles while I was writing here

and how stuff works. So um. In general, what you have is a plasma torch, which is again an ionized gas. You have a gas that's being UH that goes between two very powerful electrodes, which generates an electrical current. It ionizes the gas, and it generates an incredibly hot torch, a torch that's so hot that it can actually be

hotter than the surface of the sun. You apply this torch to garbage and it either gasifies the garbage if it's all carbon based, or it turns it into it a it turns into slag, so you get too byproducts style of this. You get a gas and you get UH. First it's a liquid slag, but if you cool it it becomes solid um. It's pretty fascinating stuff. I would

recommend reading the article. It goes into a lot more detail, but you can learn all about how ahaps using plasma torches, we could even create fuel from our garbage and UH eventually have something like a mr fusion, although again it's plasma plasma fication, not not called fusion. So thanks a lot. If any of you have any questions or suggestions, write us. Our email address is text uff at how stuff works dot com. We have articles about microwaves and other nifty

gadgets on the site. To check that out and Chris and I will talk to you again, possibly when it's snowing really soon. Plasma for moralness and thousands of other topics. Is that how stuff works dot com and be sure to check out the new tech stuff blog now on the house stuff Works homepage, brought to you by the reinvented two thousand twelve camera. It's ready are you