Why Do Grapes Spark In The Microwave?

Segment Transcript

IRA FLATOW : This is Science Friday. I ’ megabyte Ira Flatow. Physicists work to answer some of the biggest questions out there, like what is colored matter ? Can we unite relativity and quantum mechanics ? And why do grapes produce a fireball when you microwave one ?
What, you haven ’ thymine hear of that mystery ? Yes, if you microwave a grape it can explode in a violent, dangerous fireball in your microwave oven. And there are dozens of YouTube videos and scientists who have wondered about this fruitful question .
now a team of scientists, having experimented and destroyed several microwaves in the process, has an answer. And we do not recommend that you try this at home. Their results were published this week in the journal The Proceedings of the National Academy of Sciences.

My next guest is one of the authors on that analyze. Aaron Slepkov is an associate professor of physics and astronomy at Trent University in Peterborough, Ontario. Welcome to Science Friday .
AARON SLEPKOV : thank you for having me, Ira .
IRA FLATOW : You know, I had no mind that– so how many physicists have been thinking– specially you– about this motion for, what, over 20 years ?
AARON SLEPKOV : Well, I ’ ve been thinking about it for over 20 years. I was an undergraduate at a small university in 1995. And I saw a web site in 1994 that mentioned this. And we ’ ve been playing with it kind of always since as a party trick. But we haven ’ thymine been doing research on it for very long– only about five years .
IRA FLATOW : then your team decided to last put this to the test .
AARON SLEPKOV : I wouldn ’ t say we decided. I ’ five hundred say we kind of fell into it. The project actually started as a busywork visualize for some undergraduate volunteers to keep them away from my laser and my laser lab. And they made headway correct away. And it ’ s blossomed to a project that involved over seven undergrads in the last six years, or five years. And now we take it reasonably seriously .
IRA FLATOW : And you destroyed a couple of microwaves in the process. A grape can do that .
AARON SLEPKOV : Well, some were destroyed on purpose, and some were destroyed simply in the summons of taking the measurements .
A microwave oven doesn ’ deoxythymidine monophosphate like to be run empty. It ’ s a cavity that builds up department of energy. And so normally you need some kind of load– a bowl of soup, or a steak. And so if you equitable run a couple of grapes in a microwave, it can hurt the magnetron in the microwave after a while .
But we ’ ve run thousands and thousands of trials before a microwave– it doesn ’ t truly break. It just becomes less knock-down. And it moves into the food room .
IRA FLATOW : indeed give us the answer. Why does the grape explode so violently ?
AARON SLEPKOV : well, so it turns out that water is very particular as an optical fabric at microwave frequencies. So microwaves which operate at 2.5 gigahertz, urine has an index of refraction of 10, which is identical, identical high. And what that means is that microwaves can be trapped inside of a grape .
And therefore a grape is just the veracious size. It turns out to be precisely one wavelength of microwave radiation sickness farseeing. And outside of the grape, the microwave is much, much longer. So it kind of gets trapped and sucked into the grape .
so an disjunct grape has these resonant modes inside of it where it ’ mho blistering in the middle. And they don ’ thymine flicker. But when you bring two of these evocative modes close together– two grapes close up together– they kind of shackle. There ’ mho an energy hotspot– an electric plain hotspot– correct between them that can be many orders of magnitude higher than the electromagnetic energy that ’ s inside of the grapes .
so they kind of kind a bonding mode properly between them at the charge of contact. And that seems to have a gamey enough electric playing field to ionize potassium and sodium that ’ randomness in the grapes .
IRA FLATOW : Amazing. I have a tweet from Darren, who says, OK, unplayful wonder. Would carrots do this, besides ?

AARON SLEPKOV : absolutely. The carrots would have to be sliced or balled up into something roughly the size of grapes. Any fruit that ’ south water-rich .
actually, it ’ s the water. That ’ randomness one of the things that we discovered, that grapes were a moment of a loss herring. We were able to do this with hydrogel beads, which is just the lapp stuff that ’ mho in superintendent absorbent material diaper material. It grows to about the size of a grapeshot, at which point it ’ mho over 98 % saturated water. It ’ second got no skin. And just the water bottle alone is able to do that. well, two, of them in contact are able to do this. thus grapes are fine. Melon, olives, and blueberries .
IRA FLATOW : Can people at home safely set this up and try it in their microwaves ?
AARON SLEPKOV : then I ’ ve been advised not to say yes, because everybody seems to say no. I have done it at home plate hundreds of times to no ill effect .
IRA FLATOW : And tell us precisely what you did that did not produce a smash success, indeed to speak .
AARON SLEPKOV : Well, no, I ’ ve done it, and it works. If you ’ re going to try it at dwelling, the best advice is to cut the grape in half, and leave a fiddling sting of the clamber bridge. now that ’ s the traditional way of doing this experiment. And a lot of the scientists over the by few years believe that the skin bridge had something to do with the effect mechanistically .
But in truth, I think what we discovered is the skin bridge is just a way to keep the two hemispheres close in concert so that the grapes could bond in the same way that two whole grapes do work. But if you merely put two wholly grapes in a microwave, they ’ re going to roll apart, and they ’ re going to separate. vitamin a soon as the grapes are more than a millimeter or two apart, they ’ ll no long form this effect. so in all of our experiments, the grapes are in a little watch glass to bring them closer together .
But if you want to do it at home, just cut a grapeshot in one-half, leave the two hemispheres kind of bonded with a little bite of skin, and run the microwave for 10 seconds. It normally should spark within five to six seconds. If it doesn ’ deoxythymidine monophosphate spark after 10 seconds, turn off the microwave. If it does spark, turn off the microwave after about a second base or two of forming plasma .
The biggest risk is that the plasma, it can grow in a microwave, because it ’ s resonant with the microwave radiation itself. And so it can leave the region of the grapes. Hot publicize rises. The blistering plasma rises to the ceiling of the microwave. You don ’ thymine see it there. And it ’ s burrowing through the alloy, and it ’ second doing bad things. But we ’ ve never had any explosions or anything. The key is to turn off the microwave right away .
IRA FLATOW : Are there any follow up acts for you on this one ? What do you do next ?
AARON SLEPKOV : well, so Hamza Khattak, who is the undergraduate student who brought this past the finish pipeline, he ’ mho been doing some very interest simulations trying to see if this is a dynamic process that ’ sulfur running away towards resonance or running far from resonance. The point is that the water, being then matter to, changes its ocular properties as it heats up. So the fact that locally, near the point of contact, it heats up differently than everywhere else could mean that this phenomenon is self-tuning, or possibly detuning, depending on the size of a grape. So we ’ re doing some simulations .
And we ’ re besides, if you see some of the video recording that are on-line, you ’ ll notice that frequently the grapes or the hydro gels, they bounce. They vibrate very debauched. And so we ’ ra investigating this mechanical motion. We feel that there ’ s some very concern physics in the mechanical apparent motion .
IRA FLATOW : So it ’ mho actually barely a pure research plan at this consequence .
[ CHUCKLES ]
AARON SLEPKOV : Yeah, it indisputable is .
IRA FLATOW : nothing ill-timed with that. Thank you very much for taking the prison term to be with us today, Dr. Slepkov.

AARON SLEPKOV : I ’ m therefore please to be on the usher. Thank you very much for having me .
IRA FLATOW : You ’ re welcome. Aaron Slepkov, an associate professor of physics and astronomy at Trent University in Peterborough, Ontario .
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