Electromagnetic waves include: radio waves, microwaves, infrared rays, visible light, ultraviolet rays, X-rays, and γ-rays.
According to the length of the wavelength and the different wave sources, the electromagnetic spectrum can be roughly divided into:
(1) Radio waves - the wavelength ranges from several kilometers to about 0.3 meters. General TV and radio broadcasting bands use this kind of wave;
(2) Microwave - wavelength from 0.3 meters to 10-3 meters, these waves are mostly used in radar or other communication systems;
(3) Infrared rays - wavelengths from 10-3 meters to 7.8×10-7 meters; the thermal effect of infrared rays is particularly significant;
(4) Visible light - this is an extremely narrow range of light that people can detect a band. The wavelength range of visible light is very narrow, about 7600 ~ 4000 (Angstroms are often used as the unit of length to express wavelength in spectroscopy, 1=10-8 cm). It extends from visible light to both sides. The wavelength longer than it is called infrared ray. From about 7600 up to a few tenths of a millimeter. Wavelength ranges from (78~3.8)×10-6 cm. Light is an electromagnetic wave emitted when the motion state of electrons in atoms or molecules changes. Because it is the very small part of the electromagnetic wave that we can directly feel and detect;
(5) Ultraviolet light - the wavelength shorter than visible light is called ultraviolet light, and its wavelength ranges from 3×10-7 meters to 6×10-10 meters, it has significant chemical and fluorescent effects. The cause of this wave is similar to that of light waves, and is often emitted during electrical discharges. Because its energy is similar to the energy involved in general chemical reactions, ultraviolet light has the strongest chemical effect;
Both infrared and ultraviolet rays are invisible to humans and can only be detected with special instruments. Whether it is visible light, infrared or ultraviolet light, they are excited by microscopic objects such as atoms or molecules. In recent years, on the one hand, due to the development of ultra-shortwave radio technology, the range of radio waves has continued to develop in the direction of shorter wavelengths; on the other hand, due to the development of infrared technology, the range of infrared rays has continued to expand in the direction of longer wavelengths. The boundary between ultrashort wave and infrared rays no longer exists these days, and their ranges overlap to a certain extent.
(6) Roentgen rays - This part of the electromagnetic spectrum has wavelengths from 2×10-9 meters to 6×10-12 meters. Roentgen rays (X-rays) are emitted when the inner electrons of an electric atom jump from one energy state to another or when the electrons decelerate in the electric field of the nucleus; X-rays are emitted by the inner electrons in the atom. , its wavelength range is about 102 ~ 10-2. As X-ray technology develops, its wavelength range continues to expand in two directions. At present, the long-wavelength band has overlapped with ultraviolet rays, and the short-wavelength band has entered the gamma ray field. The wavelength of radioactive radiation gamma rays ranges from about 1 to infinitesimal wavelengths.
(7) Gamma rays - electromagnetic waves with wavelengths from 10-10 to 10-14 meters. This kind of invisible electromagnetic wave is emitted from the nucleus of an atom. This kind of radiation is often accompanied by radioactive substances or nuclear reactions. Gamma rays have strong penetrating power and are very destructive to living things.
Because the radiation intensity decreases sharply with the decrease of frequency, the intensity of low-frequency electromagnetic waves with a wavelength of several hundred kilometers (105 meters) is very weak and usually goes unnoticed by people.