When you microwave food, the primary heating mechanism is the absorption of microwave radiation by water molecules within the food. Microwaves are a form of electromagnetic radiation that excites the water molecules, causing them to vibrate rapidly and generate heat.
The plate or container holding the food in a microwave generally does not contain significant amounts of water molecules. Instead, it is typically made of materials like glass, ceramic, or plastic, which are not easily heated by microwaves. These materials are transparent to microwave radiation, meaning that they do not absorb it as readily as water does.
Since the plate or container does not absorb much of the microwave energy, it doesn't heat up significantly during the cooking process. However, it's worth noting that if the food itself becomes extremely hot, it can transfer some of its heat to the plate through conduction. In such cases, the plate may get warm, but the primary source of heat is still the food itself, not the microwave radiation directly.
It's important to remember that different types of containers or plates may behave differently in the microwave. Materials that do absorb microwaves, such as certain metal objects or containers with metallic accents, can cause sparking or even damage the microwave. Always make sure to use microwave-safe dishes and follow the manufacturer's instructions for safe use.