Why does a microwave oven heat food unevenly?
A microwave oven heats food by bombarding it with Microwave energy (a portion of the electromagnetic spectrum, much like visible light or radio waves). When water molecules are hit by a photons in the microwave frequency, they become excited, and move around faster – this is what causes them to heat up. Since the outer surfaces of the food are the ones exposed to the most microwaves, they tend to heat up faster than the insides. Basically, for a microwave to excite a molecule on the inside, it has to ‘miss’ all the molecules on the outside to get to it. The thicker your food is, the less likely that is to happen. What ends up happening is that the outside of the food gets heated by direct radiation, while the inside has to be heated by conduction – the transfer of heat from the outer surfaces to the inner ones directly. This process is much slower, and so you end up with food that is hot on the outside, and cold on the inside. That was longer than I anticipated, but hopefully it helps!
