But it seems the used microwave was rather old indeed, for the one we have where I work, does not even make a fuss out of metal put into it. And it is running with just dry air rather often, and someone once accidentally tested it on metal, putting in a Can of some soup.
Some liquid nitrogen to play around with might be nice though… Might freeze the circuits if someone tripped the cup… 
And may I be the first to say, “Huh?”
Welcome to the Straight Dope Message Board, The_Mac, glad to have you with us.
When starting a thread, it is helpful to others if you provide a link to the appropriate Staff Report or Column upon which you are commenting. Helps to keep folks more or less on the same page.
In this case, the Staff Report will appear on Tuesday, 14 January, and is What would happen if you put liquid nitrogen in a microwave?
If you do any further experiments, be sure to report back!
There would have been no fireworks in the microwave oven if you had put in one cup of water along with the one cup of liquid nitrogen.
Now I’m confused. How does he respond to a staff report not yet out?!
The link was published in advance in the weekly mailing as usual. Sign up here: http://www.straightdope.com/index.html#maillist
Ah, no kidding. Thanks.
Can someone please tell me what the Leidenfrost effect is.
I have to agree with Mac’s statement here – I was confused when Chronos’s report said there was a minor lighning storm in the empty microwave – our oven wouldn’t do that. It’s be interesting to try this with a newer oven, just for kicks.
Can someone please tell me what the heck Chronos is saying when he claims:
Since when does a microwave containing only air result in sparks and flashes?
I believe that the results of the Leidenfrost effect is that the liquid N2 essentially floats along as little droplets that float along the ground. I believe that since the relative temperature between the droplets and environment are so great, the outgassing results in a “cushion” of N2 gas that allows the droplet to float and bounce around like an air hocky puck. The same effect can be found by dropping drops of water on a hot frying pan.
Chronos,
I was under the impression that, ideally, a diatomic molocule had three modes of rotation; two of them would be a “spin the bottle” effect, whereas the third would be a spin about their common axis. As for the other mode wouldn’t there be some additional vibration modes such as “stretching”, “bending”, and “twisting” mode. If I recall, real N2 at room temperature only allows for the former two for spin and the “bending” for the vibration aspect as a result of quantum effects. Am I correct, or am I suffering from uncertainy in this area.?
As for odd things in the microwave, an AOL CD zapped for a second produces some beautiful “lightning” fractal patterns within the CD.
Uh…“Dropping drops of water”… how about “placing drops of water” :smack:
Ditto on minty green’s comment. The only time I’ve seen “lights and flashes” in a microwave is when I put a compact disc in one. I’ve run microwaves many times without the presence of water or anything else in them without ever seeing such a light show. 
That’s what brought me here to this little hidden cove of the boards.
What’s the deal with the light show? The only light I get from an empty microwave is the standard incandescent one that show me what’s inside?
You can rotate in three different dimensions, it’s true, but I think he was saying that they have the same frequency. A diatomic molecule has only one stretching mode, with its one frequency. There isn’t a “bending” mode – how do you bend a diatomic molecule? I did my own thesis work on cyanide – another diatomic molecule – and I used it precisely because it was so simple – only one stretching mode, along with rotational modes. Water is tri-atomic, with lotsa modes, especially if you allow combinations.
If it wasn’t clear from my post above, I’ve been asking the same question everyone else has been – why is Chonos’ microwave oven acting so weird when there’s nothing in it?
I’m not surprised that the nitrogen-in-microwave behaved about the same whether it was turned on or not (I don’t know about that “light show” thing, but that’s another matter), but there is this important tidbit:
enough liquid nitrogen in a small enough space will, if left alone for a few minutes, explode spectacularly.
So a small amount of liquid nitrogen in a large microwave will just boil off; but with the right amount (sorry, I don’t know offhand how to calculate this), the microwave will explode if its seal is airtight. This effect is best demonstrated with a 2-liter bottle to which a bit of liquid nitrogen has been added: as my chemistry teacher explained, you “do this in the middle of a football field, and run like hell”. This same teacher did it inside the chem lab (he told us to kinda hide behind the desks, and put an overturned trash can on top of the explosion-to-be).
When the nitrogen boils off, it becomes vapor; but there is a point where the pressure from all this vapor can get to be too much for the walls of the container to hold. Then again, if done in a microwave, it would probably just slam the door open violently. If you’re lucky.
CalMeacham
Thanks for the update. I was trying to cover all the modes I could think of. Still, would twisting or bending be possible?
Can a microwave put on it’s own light show? Get enough power inside of the cavity and you’ll get the sparkies. Having worked with people using 5 cm waveguides before, if you put enough power into the box the E fields can get so high as to cause arcing (always sounded like a muffled ring) within the waveguide. Of course I was working with 100 kW pulse sources so results will vary with the geometry, the the impedance of the termination load (we used a piece of maple enclosed inside of a finned cooling device; why maple? I would guess that it was an idea load for that frequency), and the power fed into the load, etc.
Would a commercial available oven do this? It’s unlikely, because more power translates to more expense (i.e., bigger magnetron) and safety concerns would increase (will the food catch on fire?).
One of the guys I worked with 20 years ago told me they use to demonstrate microwave popcorn in the 60’s during open houses. They would take a couple of cups of popcorn, put it in grocery bag tape the top and flatten the bag and put under a feed horn in the other room. When enough people came in they have a kid press the pulse button off the 100 kW source, and, ka-bamm, the bag would expand instantly. Sometimes the tape didn’t hold and it “snowed” instead. Anyway they would offer the “microwaved” popcorn to anyone who wanted it. People thought this was really cool at the time.
I wanted to ask him later if they provided any shielding for the visitors when they did this, but I’m guessing that figured that they, along with everyone else would be far enough away. I was aware of the dangers at that time because long before my Dad told me when he was in the Army in the early 50’s he worked on a fire control radar. One day he experimented by by inserting the back of his hand in front of live radar horn. He told me that nothing happened then, but the next morning, he has a hugh blister on the back of his hand. :rolleyes:
CalMeacham
Thanks for the update. I was trying to cover all the modes I could think of. Still, would twisting or bending be possible?
Can a microwave put on it’s own light show? Get enough power inside of the cavity and you’ll get the sparkies. Having worked with people using 5 cm waveguides before, if you put enough power into the box the E fields can get so high as to cause arcing (always sounded like a muffled ring) within the waveguide. Of course I was working with 100 kW pulse sources so results will vary with the geometry, the the impedance of the termination load (we used a piece of maple enclosed inside of a finned cooling device; why maple? I would guess that it was an idea load for that frequency), and the power fed into the load, etc.
Would a commercial available oven do this? It’s unlikely, because more power translates to more expense (i.e., bigger magnetron) and safety concerns would increase (will the food catch on fire?).
One of the guys I worked with 20 years ago told me they use to demonstrate microwave popcorn in the 60’s during open houses. They would take a couple of cups of popcorn, put it in grocery bag tape the top and flatten the bag and put under a feed horn in the other room. When enough people came in they have a kid press the pulse button off the 100 kW source, and, ka-bamm, the bag would expand instantly. Sometimes the tape didn’t hold and it “snowed” instead. Anyway they would offer the “microwaved” popcorn to anyone who wanted it. People thought this was really cool at the time.
I wanted to ask him later if they provided any shielding for the visitors when they did this, but I’m guessing that figured that they, along with everyone else would be far enough away. I was aware of the dangers at that time because long before my Dad told me when he was in the Army in the early 50’s he worked on a fire control radar. One day he experimented by by inserting the back of his hand in front of live radar horn. He told me that nothing happened then, but the next morning, he has a hugh blister on the back of his hand. :rolleyes:
I also want to know why/how the ‘empty’ microwave caused flashes. I was under the impression that the glass plate at the bottom of the chamber was to provide a minimum load.
What gives Chronos?
Did you take the plate out? Are you using a souped up microwave? (pun intended) Did you buy the microwave from the same guy that sold jack his magic beanstalk beans?
-Sandwriter
Once, when I was in college (UC San Diego), my chemistry professor, evidently at a loose end, came into the lab, cracked the stopcock on a canister of liquid nitrogen, and invited me to dip my finger in the stream. I told him he was crazy, my finger would freeze solid and crack off. He said, no, it’s perfectly safe, see? and stuck his own finger in. So I tried it, and sure enough, with the stuff dribbling out (not gushing), the heat of my finger vaporized it before it could touch the skin and it just flowed around. Meanwhile, blobs of liquid N2 were whizzing all over the lab floor, as described above.
College was fun.