Microwaves heat up food in an oven through a process called dielectric heating. Here's a simplified explanation of how this works:
Microwave Radiation: Microwaves are a form of electromagnetic radiation with a specific frequency range. In a microwave oven, a magnetron generates these microwaves.
Microwave Absorption: When you place food inside the microwave oven and start it, the microwaves are directed into the cooking chamber. Microwaves have a unique property - they are absorbed by certain materials, particularly those with high water content, fats, and sugars. These materials are called dielectric materials.
Interaction with Water Molecules: The microwaves are absorbed by water molecules present in the food. As the microwaves interact with the water molecules, they cause the molecules to vibrate rapidly. This vibration generates heat, which, in turn, heats up the surrounding food.
Uniform Heating: Microwaves penetrate into the food, rather than heating it from the outside like a conventional oven. This leads to more uniform heating throughout the food.
Now, as to why this method doesn't work effectively on certain materials like glass or metals:
Glass: While glass is generally transparent to microwave radiation and doesn't absorb microwaves, it can still get hot indirectly. The food in the microwave heats up, and then the heat is transferred to the glass container, causing it to warm up. However, some glass containers may have small impurities or air pockets that can absorb microwaves, making them prone to cracking or shattering if exposed to intense microwave radiation.
Metals: Metals are highly reflective to microwave radiation. When microwaves encounter metal surfaces, they reflect off them rather than being absorbed. This reflective property can lead to a concentration of microwave energy in certain areas, causing sparks or arcing and potentially damaging the microwave or the metal object. Moreover, as the microwaves don't get absorbed, they don't generate significant heat within the metal object, so it doesn't efficiently heat the food.
It's essential to use microwave-safe containers made explicitly for microwave cooking to avoid accidents and ensure even and safe heating of food. These containers are designed to handle the unique properties of microwave heating without becoming damaged or causing any safety issues. Always follow the manufacturer's guidelines and recommendations for microwave use to maintain safety and prevent damage to both the microwave oven and the cookware.