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In the big lines, this what I understand :


    • Why do grapes contains ions ?

    • How is that link broken ?

    • What is this gas made of ? water ? sugar ?


Is that correct ?




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Variation on the theme. If you put carbon fibers in a microwave, they immediately burn. If you put them in an evacuated tube, they glow like a light bulb filament. –  mmesser314 Mar 5 at 14:30

4 Answers 4




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""Plasma means a large population of free electrons and ions, as opposed to a flame which just has a large population of excited-state electrons."" What are "exited-state-electrons? Most flames contain a lot of ions! –  Georg Sep 20 '12 at 15:57

Plasma is a state of matter which is composed entirely of charged particles or ions. By this definition, a flame is a plasma in itself because it consists of charged particles. This can be demonstrated by placing a flame in a uniform electric field. The flame bends to a side in presence of a field. It may also be due to the fact that an electric field ionizes some constituents in the flame, causing it to be affected by the electric field itself. In either case, it is not wrong to call a flame some sort of a "cold plasma". If a grape bursts into flame when put in the microwave, I do not think that people are wrong to call it plasma by any standards. As far as your question is concerned, you already have your answer.

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There are quite a few questions here:

1a) Because any living organism contains ions. (Scientist can not answer the question "why" they answer the question "how").

1b) From the video, it seems to be working for any size of grape (you can try at home). The microwave frequency used in oven is the water molecule rotation frequency.


That must weaken the link.

The arc can be up to a few thousands volt.


3b) An electric arc through a gas is a plasma. Plasma temperature varies from a thousand degrees to several millions. Joule effect and microwave heating are responsible for this temperature.

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Nonetheless, it is a myth that microwave ovens operate at any resonant frequency of water. –  user27118 Mar 6 at 19:55
another myth? . A link to a doc by Popa, Adrian (23 December 1997). "Re: Why do grapes spark in the microwave?". MadSci Network. Retrieved 23 February 2006. –  Helder Velez Mar 14 at 2:35

Usually, the microwaves are too weak to heat anything to a plasma state. However, if you bypass the manufacturer’s instructions and turn on the microwave with nothing in it to absorb energy, the microwave energy density will be much higher than normal.

Now, the reason you cut the grape in half is:

"Now it turns out that grapes are just the right size to further focus the electric fields in the oven. Two grapes placed close but not quite touching will produce a large field between them, sometimes enough to make a plasma."

source: https://van.physics.illinois.edu/qa/listing.php?id=818

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protected by Qmechanic Apr 17 '14 at 6:42


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