Why Can’t I Put Metal in the Microwave?

Why Can’t I Put Metal in the Microwave?


You’ve probably been told, or maybe learned
the hard way after heating a burrito wrapped in tinfoil, that you shouldn’t put metal in
the microwave. But your curious scientific mind might have noticed that your microwave
is…made of metal. And there’s even that metal mesh covering the window. And isn’t
that Hot Pocket pouch lined with aluminum? So what the heck? When do microwaves and metal
play along fine, and when do they end up burning down your house? Well, the heart of your microwave
oven is a magnetron, a high-powered vacuum tube that generates microwaves. The magnetron
sends microwaves, which, like radio waves, are a type of electromagnetic radiation, into
that little box where your food rotates around. And the little window on the door is covered
with a metal mesh because that forms what’s called a Faraday cage. The holes in the mesh
are smaller than a microwave’s wavelength, so they keep those waves from passing through
the door and cooking off your face. Safely contained in the box, these microwaves
can pass through glass, paper, and plastic until they’re absorbed by the water molecules
in your food. They heat up until, suddenly, your burrito is no longer frozen. But metals…metals
are a different story. They’re full of free-moving electrons, so they conduct electricity like
nobody’s business. How microwaves respond to metal, though, can depend on the metal’s
thickness and shape. The walls of your microwave oven, for instance, are thick and flat, so
when microwaves strike them, the electrons in the metal vibrate back and forth, but the
microwaves just bounce off. But when a piece of metal is really thin, like a piece of foil,
it’s less able to withstand all of that electron activity, and it heats up really fast. Before
you know it, it can ignite. Plus, most metal objects like forks and wads of foil have curves
and corners. These features can cause microwaves to produce concentrated electric fields along
the points and edges. This charge buildup can ionize the air around the object, which
is what makes that terrible popping noise, and if the buildup gets high enough, it’ll
shoot out a powerful arc of electricity to the nearest metal object: usually, the wall
of your microwave. And then you have to go appliance shopping. And yet, some processed foods like pies, soups,
and Hot Pockets take advantage of the fact that thin sheets of microwaved metal can turn
super hot super fast. These foods are packaged with a thin metallic layer that’s coated with
a nonmetallic material on the outside, so the food that touches the metal inside browns
up quickly. But even those foods need to be watched carefully because if they’re left
inside for too long, they could burst into flames. So in the end, it turns out you can put some
metal in the microwave, if you’re careful. But, I mean, why risk it? You could ruin your
kitchen. Or your burrito. Thanks for asking, and thanks to our Subbable
subscribers who keep these answers coming. If you have a quick question, let us know
on Facebook and Twitter or in the comments below, and don’t forget to got to youtube.com/scishow
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100 thoughts on “Why Can’t I Put Metal in the Microwave?

  1. Not all magnetrons are vacuum tubes! ones I pulled from microwave ovens were not. they're just fancy diodes with external magnetic fields and internal resonant cavities made of copper 😉 eh close enough.

  2. I leave the wire whip in the glass bowl when I make lemon curd and hollandaise sauce and I''ve never had a problem. I also leave the spoon in the cup when making cocoa, again no prob. I have left forks in things also, but they were specific to a recipe and only done at the suggestion of a cook who designs recipes for microwave cooking. My lemon curd is super btw.

  3. him: ''you could ruin your kitchen…''
    me: ''pfff like I care…''
    him: ''…or your burito.''
    me: ''NNNNOOOOOOOOOOOOOOOO''

  4. I put a metal cup in the microwave and turned it on and the handle touched the wall and burned the microwave wall and it turned black

  5. I hate how people on science channels insult others when they bring up topics about God, I mean many famous scientist believed in God like Michael Faraday.

  6. My little sister set a Capri Sun on fire in the microwave… It was frozen and she was trying to thaw it out. Well, the pouch had just enough metal that "blue lighting" went off inside and it started to burn. I had no idea they were even flammable. I'm glad I was there because she was freaking out lol

  7. Who else thinks when they talk about the micro waves in the microwave you think teeny tine little microwaves

  8. Interestingly, I asked my incompetent physics teacher this question and she gave the vaguest answer I ever heard.

  9. what about the microwaves with the metal rack in the middle? like an oven would have? Thats small and curved metal, why wouldn't it have the same effect?

  10. I think the real question I want answered is why the microwave I used as a child had a metal shelf in it and had zero issues with metallic substances being present during operation and why I haven't seen one like it in years.

  11. We had this dude at my work that microwaved tinfoil and caught the microwave on fire. Our boss ran in with a fire extinguisher. The foil guy thought was hilarious.

  12. People say we literally stick to a live wire when electricity catches us or the other way round.But…..
    Does that actually happen?

  13. I would really like to understand how microwaves work.

    Nothing I've read has explained it in a way I understand.

  14. I like how you said, “It could run your kitchen, or your burrito,” because the burrito is obviously more dramatic and important! : )

  15. One time I wanted ro make a hot dog but i wanted it on a stick so I got a metal rod and put I in the got dog nothing happened until the rod thouched the edge it make sparks and burn marks and sounded like a Jacobs ladder

  16. Learned that when I tried to thaw out a chocolate bar in its wrapper. No damage done, but my candy was ruined.

  17. I wonder, if you put the All Spark inside a microwave, would it start shouting "Prime!" and calling for his Decepticons.

  18. A girl put a entire metal thing in the microwave once at Wal-Mart and it worked for a bit till she closed the microwave after she was done an that was when the fun started happening, it would not shut off and sparks started happening inside it with nothing inside.

  19. I've only microwaved metal once in my life. I was at work and needed to warm up some burger buns. We put them in the microwave all the time to do the initial defrost. I forgot to undo the twist-tie. The metal inside heated up and set fire to the paper part of the twist-tie. Melted plastic and a fire slightly larger than a candle. NBD.

  20. So how exactly do microwaves work and, if they send out a type of radiation, how do they supposedly NOT irradiate food?

  21. I used to have old dishes with a thin gold rim. When I used them in the microwave, purple sparks danced around the edge.

  22. I put spoons in the microwave all the time because they have no crinkles to set up high voltages. Forks are another story though. Wouldn't risk it with them.

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