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When you cook food in a microwave oven, why doesn't the plate get cooked?

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closed as unclear what you're asking by AccidentalFourierTransform, user191954, Bill N, ZeroTheHero, Jon Custer Nov 28 '18 at 3:30

Please clarify your specific problem or add additional details to highlight exactly what you need. As it's currently written, it’s hard to tell exactly what you're asking. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ What is an uncooked plate? $\endgroup$ – JMac Nov 27 '18 at 13:36
  • $\begingroup$ Do you think a sample of water in a microwave gets 'cooked'? $\endgroup$ – user191954 Nov 27 '18 at 14:53
  • $\begingroup$ @Chair Regarding putting on hold, I respectfully feel it is common for people to wonder why the food in a microwave oven gets hot but the plate not nearly so. The plate getting "cooked" is probably a poor choice of words, but I think we know what is meant. $\endgroup$ – Bob D Nov 28 '18 at 22:18
  • $\begingroup$ @BobD If that was the intended meaning, I would think there's somewhat poor prior research since every article regarding the functioning ov microwave ovens would cover that. There's also a high likelihood that there's a duplicate out there somewhere. That being said, this question is somewhat borderline, so you could feel free to make a meta post to ask if it can be reopened. $\endgroup$ – user191954 Nov 29 '18 at 0:33
  • $\begingroup$ @Chair I agree.But I find there are a lot of questions that could be answered by doing good prior research, but they are not all put on hold. Understand it is a judgement call. $\endgroup$ – Bob D Nov 29 '18 at 0:45
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Microwave ovens primarily operate at 2450 MHz, which corresponds to a photon energy level about $10^{-5}$ eV. This energy level is within the range that separates molecular rotation and torsion quantum states. The photon energy associated with molecular vibration is in the range of 0.001 to 1.7 eV (ref: Hyperphysics Interaction of radiation with matter), well above the microwave energy level.

The wavelength of the microwaves is about 12 cm. The peak absorption of water (due to dielectric loss) occurs at a lower wavelength, but the range is broad and encompasses 12 cm. The design of a microwave oven’s frequency is more about the need for the FCC to assign values taking into account the needs of other equipment, than it has to do with ideal water absorption. However, water absorption is the primary mode of increasing the temperature of food items.

Finally, the dielectric loss of water is greater than the dielectric loss of glass (a primary component of a plate). Thus the increase in temperature of water is significantly greater than that of the plate exposed to microwaves.

Hope this helps.

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Water is a polar molecule (it has positive and negative charged parts) and interacts with microwaves (exciting vibrational and rotational modes) very much better than the non-polar molecules of which the containers are made. In effect the containers are transparent to microwaves whereas the food which contains water molecules is not.

The container etc will get hot by the conduction of heat from the food which is a relatively inefficient process.

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  • $\begingroup$ if the container is made of something which is even slightly electrically conductive, then the microwaves will set up current flow in that material and it will get hot as well. I have several homemade ceramic platters and bowls that have enough conductivity that they get very hot in my microwave under conditions where my pyrex cookware will not get hot at all. $\endgroup$ – niels nielsen Nov 27 '18 at 19:03

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