Microwaves heat an object through a process called dielectric heating, also known as microwave heating or radiofrequency heating. Here's a step-by-step explanation of how microwaves heat food or other objects:
Generation of microwaves: Microwaves are electromagnetic waves with a specific frequency range, typically around 2.45 gigahertz. In a microwave oven, these microwaves are generated by a device called a magnetron. The magnetron converts electrical energy into microwave radiation.
Penetration of microwaves: The microwaves generated by the magnetron pass into the cooking chamber of the microwave oven. The microwaves are designed to be transparent to most materials, such as glass and certain plastics, but they can be absorbed by certain substances, particularly water, fats, and some other molecules with dipole moments.
Interaction with polar molecules: When microwaves encounter polar molecules in the food (or object), such as water molecules, the electric field of the microwave causes these molecules to oscillate or rotate. Polar molecules have an uneven distribution of electric charge, resulting in a positive and negative end (a dipole). The oscillating electromagnetic field of the microwave causes these polar molecules to constantly try to align themselves with the changing field.
Molecular agitation: As the polar molecules attempt to align with the rapidly changing electric field, they undergo rapid vibration and rotation. This agitation generates kinetic energy, increasing the internal energy and, consequently, the temperature of the material.
Transfer of heat: The kinetic energy generated by the molecular agitation is transferred as heat to the surrounding material. In the case of food, this heat is what cooks or heats the food.
Uniform heating: Microwaves can penetrate the food from multiple directions, which contributes to more uniform heating compared to traditional cooking methods, where heat is primarily conducted from the surface inward.
It's important to note that not all materials are equally affected by microwaves. Substances with polar molecules, like water, fats, and some other compounds, are more effectively heated by microwaves. Materials with non-polar molecules, such as certain plastics and glass, are generally transparent to microwaves and do not heat up significantly when exposed to microwave radiation. This is why microwave-safe containers are chosen based on their ability to withstand microwave energy without absorbing or releasing harmful substances.