Final answer:
Microwave ovens use electromagnetic waves to generate heat in food through the absorption of microwaves by water molecules. This absorption causes the water molecules to rotate faster, producing heat that cooks the food.
Step-by-step explanation:
When using a microwave oven to cook food, electromagnetic waves are used to generate heat. The microwaves in a microwave oven have a specific frequency, typically around 2.45 GHz, that is absorbed by water molecules present in the food. This absorption causes the water molecules to rotate faster, generating heat that cooks the food.
For example, when microwaves at 2.45 GHz are produced by accelerating electrons, they create an alternating electric field in the oven. The oscillating electric field exerts a torque on the water molecules, causing them to align in different directions and vibrating their thermal motion, which results in the heating of the food.
It is important to note that most plastics and glass do not become hot in a microwave oven because they lack water molecules, which are the main source of absorption for the microwave energy.