Inside a microwave oven, the waves used for cooking are called "microwaves." These microwaves are a type of electromagnetic radiation, similar to radio waves, but they have a much higher frequency and shorter wavelength. Microwaves have a frequency range between 300 megahertz (MHz) and 300 gigahertz (GHz), with the microwaves in ovens typically operating at a frequency of 2.45 GHz.
The reason why you can't see microwaves is that they are outside the visible spectrum of light. The visible spectrum is the range of electromagnetic radiation that our eyes are sensitive to, and it includes colors from violet to red. Microwaves have a much lower frequency than even the lowest frequency visible light (red light), so they lie beyond the violet end of the spectrum. This means our eyes are not equipped to detect microwaves.
While you can't see microwaves directly, you can still observe their effects when they interact with certain materials, such as food. When microwaves enter the oven and come into contact with food, they cause water, fats, and sugars in the food to vibrate. This molecular vibration generates heat, which cooks the food.
The design of microwave ovens is also a crucial factor in preventing the microwaves from escaping and being visible to the human eye. The oven's metal enclosure acts as a Faraday cage, which contains the microwaves inside, ensuring they don't leak out and potentially harm people nearby.
So, while you can't see the microwaves themselves, you can certainly observe their practical effects in cooking your food efficiently and quickly.