Microwaves heat food primarily through a process called dielectric heating, which relies on the interaction between the electromagnetic waves generated by the microwave oven and the water molecules in the food. Air can also be indirectly heated by microwave through this process.
Here's how it works:
Microwave generation: The microwave oven produces electromagnetic waves, which are a type of high-frequency radio wave. These waves have a specific wavelength that is designed to be absorbed by water molecules.
Absorption of microwaves: When you place food containing water in the microwave oven, the electromagnetic waves penetrate the food and are absorbed by the water molecules present in the food.
Vibrational energy: As the microwaves are absorbed, they transfer their energy to the water molecules, causing them to vibrate rapidly. This rapid molecular movement creates friction and generates heat.
Transfer of heat: The heat produced by the vibrating water molecules is then conducted throughout the food, gradually increasing its temperature.
Now, you may wonder how air gets heated in a microwave. While air itself does not directly absorb microwave radiation as effectively as water, it can still get heated in the microwave indirectly through a secondary process:
Conduction from food: As the food inside the microwave gets heated, it also heats the surrounding air through conduction. The hot food comes into contact with the air molecules, transferring some of its heat energy to them.
Radiation: Some of the microwaves generated by the oven may interact with air molecules and cause them to vibrate slightly, although this effect is much weaker than the direct interaction with water molecules. Nonetheless, this contributes to the heating of the air to a lesser extent.
It's worth noting that microwave ovens are generally designed to focus the majority of the microwave energy on the food and not the air. As a result, while the air in the microwave may get warmer due to the processes described above, it won't get as hot as the food being heated. The primary purpose of a microwave is to cook or heat food efficiently, and the heating of the air is a side effect rather than its main function.