Microwaves are used for cooking, weather mapping, radar and satellite communications, as well as cellular phones, over-the-air television signals, GPS navigation and long-range telescopes. The longest frequencies are used in telescopes, while the shortest frequencies are used in GPS and cellular phones.
Microwaves are lower in frequency than infrared radiation, but higher in frequency than radio waves. They fall in the lower-energy end of the electromagnetic spectrum, while only radio waves carry less energy than microwaves. Their low energy makes them useful in detecting objects that are too dim or cool to detect through other forms of electromagnetic radiation, hence their utilization in astronomy.
Microwave ovens cook by transferring energy to the water found in food. The microwaves excite the water, which, in turn, heats the rest of the food. Non-lethal weaponry based on microwave technology uses the same principle. The microwaves heat the surface of human skin to an uncomfortable temperature, causing the target to move away. Microwaves are also used in this manner to heat fuel in nuclear reactors.
Microwaves are a form of non-ionizing radiation, and they do not carry sufficient energy to damage human DNA. Acute exposure to high-energy microwave frequencies can cause ordinary thermal burns, which are identical to those caused by any other heat source.