@Philip Wood says that microwaves cook food through because of water- https://physics.stackexchange.com/a/426958/147307

I know that microwaves excite water, and I know form experience that radiative heat transfer can leave food burnt on the outside and frozen on the inside. But I never really thought about why different EM radiation behaves differently with different materials. If I used infrared radiation to heat water (and somehow "disabled" conductive/convective heat transfer) could I have an ice cube surrounded by boiling water?

Is there a material property that can be used to predict what wavelengths will be absorbed, reflected, or pass right through?

Does visible light pass around air and water molecules, or does it pass through them?


Microwaves happen to have a frequency that is resonate with the bonds between the hydrogen atoms and the oxygen in the water molecule. The microwave energy goes into exciting that resonate mode, causing heat. Other molecules will have different bonds that resonate at different frequencies and not have the same response.

If you had a different material with known molecular structure, specifically the resonances, you could probably predict which materials would respond to a given wavelength of light. In doing so, you also need to consider the degree to which the material is transparent to the wavelength you choose so that you know how much of the volume is directly heated versus, say, the surface getting heated and the conducting to the interior.

As for why some many things absorb microwaves, it's because many things (especially the food that you put in your microwave oven) have relatively large amounts of water. It's the water that's getting heated directly.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.