It is known that the Foucault currents prevent the microwaves to leave a microwave oven (MWO). The waves can not pass tru several times smaller openings than their wavelength because the grid of the door is metallic. But how is then explained that the meal covered by Al folio can cook in MWO? I read that is dangerous but nevertheless meal is warmed up.
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1$\begingroup$ Covered by, or fully enclosed in? $\endgroup$– Jon CusterCommented May 13, 2022 at 19:46
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$\begingroup$ The oven (if it survives your experiment) doesn't just direct microwaves into the food from above, it applies then from all directions. If you did actually completely surround the food with foil, the food would not heat up (except from conductive heating from the now-hot foil) $\endgroup$– The PhotonCommented May 13, 2022 at 19:47
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$\begingroup$ Will it heat up when covered with cook paper? The holes in the paper are smaller then the microwaves I suppose. Will the radiation pass tru smaller openings that its WL? $\endgroup$– MercuryCommented May 14, 2022 at 8:49
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1 Answer
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If you completely enclose food in aluminum foil in a microwave oven, the microwaves will not penetrate the foil but will be reflected off it instead. the food inside will not be heated, and microwave radiation will build up inside the oven to levels which may be sufficient to cause the magnetron tube to fail and the oven to be ruined.
Electrical arcing will occur at places in the foil covering where the layers of foil are not in good electrical contact with each other.
Do not try experiments like this at home!
answered May 13, 2022 at 23:57
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$\begingroup$ Then how do you comment this: iforgotitswednesday.com/can-you-boil-food-wrapped-in-foil $\endgroup$– MercuryCommented May 14, 2022 at 8:45
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$\begingroup$ for conducted heat a thin layer of aluminum foil is not a barrier to the passage of heat. Heating by microwaves is NOT conductive, it is radiative. $\endgroup$ Commented May 14, 2022 at 17:44