Question

If the microwaves that a microwave creates can't penetrate the mesh on the window looking into the microwave, how does it supposedly penetrate and cook food from the inside out?

Answer 1

Microwaves used in microwave ovens are a form of electromagnetic radiation, specifically in the microwave frequency range. They are designed to penetrate and interact with food to heat it from the inside out. The process involves several key principles:

1. Microwave Frequency: Microwaves operate at a frequency of around 2.45 gigahertz (GHz) or 2,450 megahertz (MHz). This frequency is chosen because it matches the resonant frequency of water molecules, which are present in most food items. When microwaves at this frequency are generated and directed into the oven, they interact with the water molecules present in the food.

2. Dielectric Heating: Water molecules have a positive end (hydrogen) and a negative end (oxygen), which makes them polar molecules. The alternating electric field of the microwaves causes the water molecules to rapidly switch direction, resulting in friction and the generation of heat. This phenomenon is known as dielectric heating.

3. Penetration: While microwaves can easily penetrate most common food items, they have difficulty passing through metals. The metal mesh on the window of a microwave door acts as a Faraday cage, which blocks the microwaves from escaping and protects the user from direct exposure to the radiation. However, the holes in the mesh are much smaller than the wavelength of the microwaves, preventing them from passing through.

Inside the microwave oven, the microwaves are generated by a component called a magnetron. These microwaves are then distributed throughout the cooking cavity by a waveguide, which is a metal channel that directs the waves into the oven. The microwaves bounce off the metal walls and are absorbed by the food, heating it from within.

It's important to note that although microwaves penetrate and heat food from the inside, they don't necessarily cook food uniformly. Uneven distribution of microwaves and differences in food composition can lead to hot and cold spots within the food. That's why it's often recommended to stir or rotate food during microwave cooking to ensure even heating.