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I often "touch test" microwaved food to see if it is heated up enough to my preference. In doing so, I sometimes notice the characteristic tingle of a static discharge between the food and my finger (pretty sure I've at least once or twice seen a tiny spark). This comes as a bit of a surprise because I would not have expected there to be any way a static potential could have accumulated between myself and the contents of a plate in the oven from the time I put it in to the time I open the door and "touch test". I notice this often with foods that have a moderate amount of moisture - a piece of meat, cooked vegetables, mashed potatoes, etc.

This leads me to wonder whether the action of the microwaves could somehow induce a static charge - large enough to notice as either visible spark or at least feel - and that could linger after the oven shuts off for the amount of time it takes to open the door, reach in, and touch it. I don't believe I've picked up and retained a charge on my person - I've just opened the oven's door - I should be at the same electrostatic potential as the oven itself.

My understanding of electronics and physics tells me that microwaves are an alternating electromagnetic field - not something that could produce a static charge without at least something to act as a rectifier. I can't imagine that such a mechanism could "just happen" to exist in food on a plate.

Could microwave energy continue to resonate within the oven even after power has shut off? If so, could this explain the small but noticeable discharge? I would expect any such resonances to decay to practically nothing almost instantaneously, but could this be wrong?

Since the microwave oven in question has a turntable, is the explanation unrelated and more mundane: triboelectricity from the action of the turntable?

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  • $\begingroup$ en.wikipedia.org/wiki/Non-ionizing_radiation $\endgroup$ – Phoenix87 May 23 '15 at 16:31
  • $\begingroup$ Have you tried microwaving one of the same frozen foods the same amount of time in the same dish but without the turntable? If the turntable is involved one way or the other then you shouldn't feel a discharge without it... (It could be some sort of triboelectric effect.) $\endgroup$ – user42076 May 23 '15 at 16:46
  • $\begingroup$ @NoEigenvalue no, but thanks... you've helped me to improve the wording in my question. $\endgroup$ – Anthony X May 23 '15 at 17:22
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    $\begingroup$ have a look here gizmodo.com/… "Sometimes the electromagnetic field within the microwave can get a little mixed up and generate small arcs of electrical discharge. This can be caused by innocuous items like carrots (when grown in mineral rich soil) and hot dogs (when the salt and additives aren't properly mixed). " So electric fields do build up possibly because of inhomogeneities in the distribution of salts or whatever within the organic material. $\endgroup$ – anna v May 23 '15 at 18:18
  • $\begingroup$ I think an experiment to rule out triboelectric it's should be easy. I must say I am surprised at your observation - especially since moist food tends to generate vapor which will "bleed off" static electricity. Experiments are needed... $\endgroup$ – Floris May 23 '15 at 20:22

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