This 'thermal imaging' is useful for detecting people in the dark. Visible light is the light we can see. It is used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver.
Radio waves, microwaves, infrared and visible light The behaviour of an electromagnetic wave in a substance depends on its frequency. Radio waves Radio waves are used for communication such as television and radio. The electromagnetic spectrum Radio waves - Higher Radio waves are transmitted easily through air. Microwaves Microwaves are used for cooking food and for satellite communications. Microwaves - Higher High frequency microwaves have frequencies which are easily absorbed by molecules in food.
Infrared Infrared light is used by electrical heaters, cookers for cooking food, and by infrared cameras which detect people in the dark. Infrared - Higher Infrared light has frequencies which are absorbed by some chemical bonds. Astronomical objects that have a changing magnetic field can produce radio waves.
Data pictured below show emissions from a variety of sources including radio bursts from the Sun, the Earth, and even from Jupiter's ionosphere whose wavelengths measure about fifteen meters in length. Radio telescopes look toward the heavens to view planets, comets, giant clouds of gas and dust, stars, and galaxies. By studying the radio waves originating from these sources, astronomers can learn about their composition, structure, and motion.
Radio astronomy has the advantage that sunlight, clouds, and rain do not affect observations. Since radio waves are longer than optical waves, radio telescopes are made differently than the telescopes used for visible light. Radio telescopes must be physically larger than an optical telescopes in order to make images of comparable resolution. But they can be made lighter with millions of small holes cut through the dish since the long radio waves are too big to "see" them. The Parkes radio telescope, which has a dish 64 meters wide, cannot yield an image any clearer than a small backyard optical telescope!
In order to make a clearer, or higher resolution, radio image, radio astronomers often combine several smaller telescopes, or receiving dishes, into an array. Together, these dishes can act as one large telescope whose resolution is set by the maximum size of the area.
The VLA consists of 27 antennas arranged in a huge "Y" pattern up to 36 km across roughly one-and-one-half times the size of Washington, DC. The techniques used in radio astronomy at long wavelengths can sometimes be applied at the shorter end of the radio spectrum—the microwave portion. The VLA image below captured centimeter energy emissions around a black hole in the lower right and magnetic field lines pulling gas around in the upper left. If we were to look at the sky with a radio telescope tuned to MHz, the sky would appear radically different from what we see in visible light.
Instead of seeing point-like stars, we would see distant pulsars, star-forming regions, and supernova remnants would dominate the night sky. Radio telescopes can also detect quasars. The term quasar is short for quasi-stellar radio source. Non-ionizing radiation does not have enough energy to remove electrons from an atom. Visible light is another type of non-ionizing radiation. RF radiation has lower energy than some other types of non-ionizing radiation, like visible light and infrared, but it has higher energy than extremely low-frequency ELF radiation.
If RF radiation is absorbed by the body in large enough amounts, it can produce heat. This can lead to burns and body tissue damage. Although RF radiation is not thought to cause cancer by damaging the DNA in cells the way ionizing radiation does, there has been concern that in some circumstances, some forms of non-ionizing radiation might still have other effects on cells that might somehow result in cancer.
Some people can have significant RF exposure as part of their jobs. This includes people who maintain antenna towers that broadcast communication signals and people who use or maintain radar equipment. Most people are exposed to much lower levels of man-made RF radiation every day due to the presence of RF signals all around us. They come from radio and television broadcasts, WiFi and Bluetooth devices, cell phones and cell phone towers , and other sources. Microwave ovens work by using very high levels of a certain frequency of RF radiation in the microwave spectrum to heat foods.
When food absorbs microwaves, it causes the water molecules in the food to vibrate, which produces heat. Microwaves do not use x-rays or gamma rays, and they do not make food radioactive. Microwave ovens are designed so that the microwaves are contained within the oven itself. The oven only makes microwaves when the door is shut and the oven is turned on. When microwave ovens are used according to instructions, there is no evidence that they pose a health risk to people.
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