Almost all electromagnetic radiation can heat up objects.
Why do microwaves heat up food, but other electromagnetic waves with higher energies (like UV and visible light) do not?
Microwaves do a better job of heating food for two simple reasons:
- They penetrate. Microwaves in a consumer microwave oven have a wavelength of 5 inches, whereas visible light or UV has such a short wavelength that it only heats up the skin like a conventional oven.
- They are absorbed by water. Visible light passes right through water.
Also, since the frequency used in microwave ovens is chosen to be good at heating up water, it is also a frequency that will not interfere with any microwave radio or TV communications. A frequency that is absorbed by rain is not useful for communications.