I’m sure it’s because the spoon is in liquid, by why doesn’t it spark and fizz and make noise, the way metals do otherwise when put in a microwave?
Metals don’t usually spark and fizz. Hell, the entire inside of the oven is metal.
If you put really thin metal, like plating on china, into the microwave oven, it can burn out because it can’t handle the current. Is that what you’re thinking of?
A spoon in liquid, if it’s big enough, can have the effect of focusing microwaves on a small region of the liquid. Spoons are sort of spherical in shape. But tablespoons and the like are too small relative to the microwaves, I think - you need something more like a ladle, or even a metal bowl.
I had heard that there were some new microwaves that would let you microwave metal - could it be one of those?
It’s a pretty common myth that you can never put any metal in any microwave ever, and it’s a pretty false myth.
The truth is, it all depends on the microwave, the type of metal, the shape and size of the metal, and where it might be in relation to other things.
For instance, Alton Brown once had on his show a method to making microwave popcorn involving a paper bag sealed with staples…metal staples, yet nothing bad happened. Why? One, the staples are very small, so the microwaves sort of “pass over” them, two, they never came close to another piece of metal (the wall of the microwave or the other staple.) That’s when arcing can occur. The electrons in a piece of metal get really excited and want to go someplace, and if a piece of metal at a different potential is nearby, they’ll jump to it. Since your spoon was in the middle, all by itself, there wasn’t any where for the electrons to arc to. But I wouldn’t recommend leaving a mug with two spoons in there.
Some newer microwaves aren’t as easily damaged by putting metal in them. That doesn’t mean you are supposed to just shove huge chunks of metal in there any old time you feel like it. It just means that the microwave isn’t as likely to be damaged if you do.
A microwave is just a magnatron (a little thing that spins around and makes radio waves) and a metal box. The radio waves go into the metal box and get absorbed by your food, which makes your food get hot. If there’s a chunk of metal in the microwave, some of the radio waves might end up getting reflected back into the magnatron. On older microwaves the magnatron was fairly delicate and could easily be damaged by this. Newer microwaves are a bit more robust.
Any bits of metal inside the box are going to act like radio receivers. In something relatively big and flat, the radio waves are just going to circulate around in the spoon. Because the spoon is reasonably thick, the currents induced in the spoon by the radio wave don’t cause much heating. But, if you have a very thin piece of metal, you’ve got a fair amount of current going through a much thinner piece of metal, and the metal will heat up accordingly. This is how those little metal foil sheets in things like microwave pizzas work. The metal foil gets hot, but because there aren’t any sharp edges and any place where charge can easily accumulate, you don’t get any sparks.
Steel wool, on the other hand, has lots of tiny bits of metal that will heat up and glow, and also has lots of little gaps that the charge can jump across and make arcs. Steel wool and CDs (don’t try to play it afterwards!) make some of the most spectacular light shows inside of a microwave. A grape cut in half makes a surprisingly good show as well. A spoon by itself won’t spark, even if it’s not in liquid. If it’s a very thin spoon though it might get really hot really quick.
I should probably insert one of those “DON’T TRY THIS AT HOME” disclaimers right about here. Not responsible for damage you do to your own microwave oven, etc. etc. or if you burn down your house or anything.
My microwave came with a metal shelf, and a metal thermal probe for meat. As others have posted, it is thin metal films where the issues arise.
I’ve made the mistake of reheating chinese in the take out cartons and touching the wire bails as I was removing it. Owie, owie!
I have a M/W that I purchased from Sears in 1980, I’ve accidently put metal objects in it and it’s still working after 27 years.
A few details on the magnetron: Imagine a metal post placed inside a hollow metal cylinder. Embedded in the walls of the cylinder are small holes leading to precisely-sized cavities in the metal; air is completely evacuated from the open part between the post and cylinder. A magnet is wrapped across the top and bottom of the cylinder such that the magnetic field is parallel to the central post, and a heating filament is used to get the post (and cavity-lined cylinder) very hot.
Now apply a high voltage between the surrounding cavity (+) and the post (-). Electrons from the heated post will “boil off” the center and fly toward the outside cylinder. However the magnetic field will deflect these electrons into a path such that they curve back and either slam into the post or move in an orbit around it. The cavities around the cylinder provide a resonance such that orbiting electrons begin to “bunch up” in a preferred pattern as they orbit (more or less) the center post. The bunched moving electrons will then produce and electromagnetic wave at resonance with the cavities; these are fed via waveguides to the open cavity where you cook your food.
A similar device called a klystron does the same job by using an electron gun, bunching electrons in a linear path and hence not requiring a heavy magnet (where most of the weight comes from in a microwave oven). However the klystron tube has to be much larger to achieve the same effect, so you trade size for weight. I believe (need a cite here) that industrial microwaves use a klystron rather than the more compact magnetron, but would prefer an expert weigh in on this fact…