In a microwave oven, the heating element is a device called a magnetron. The magnetron is a vacuum tube that generates electromagnetic waves in the microwave frequency range, usually around 2.45 gigahertz. These waves are known as microwaves.
Inside the microwave, the magnetron directs the microwaves into the cooking area. When you set the cooking time and power level on the microwave, the magnetron activates and emits these microwaves. The microwaves penetrate the food and cause water molecules within the food to vibrate rapidly. This vibration generates heat, which cooks or reheats the food.
It's important to note that the microwaves generated by the magnetron are not the same as radio waves used for communication, but they are a type of electromagnetic wave with a much higher frequency and shorter wavelength. The design of the microwave oven ensures that these microwaves stay confined to the cooking area and do not leak out during operation, making them safe to use when used properly and with intact door seals.