NEET Physics Notes Electromagnetic Wave – Various Electromagnetic Radiations
Various Electromagnetic Radiations
Various Electromagnetic Radiations Gamma rays
They were discovered by Becquerel and Curie in 1896. Their wavelength is of the order of 10-14m to 10_10m The main sources are the natural and artificial radioactive substances. These rays affect the photographic plate. These rays are mainly used in the treatment of cancer disease.
X-rays
They were discovered by Roentgen in 1895. Their wavelength is of the order of 10-12m to 10-8m. X-rays are produced, when highly energetic cathode rays are stopped by a metal target of high melting point. They affect the photographic plate and can penetrate through the transparent materials.
They are mainly used in detecting the fracture of bones, hidden bullet, needle, costly material etc., inside the body, and also used in the study of crystal structure.
Ultraviolet Rays
They were discovered by Ritter in 1801. Their wavelength is of the order 10-9 m to 4 x 10-7m. In the radiations received from sun, major part is that of the ultraviolet radiation. Its other sources are the electric discharge tube, carbon arc etc.
These radiations are mainly used in excitation of photoelectric effect and to kill the bacteria of many diseases.
Visible Light
This was first studied in 1666 by Newton. The radiations in the range of wavelength from 4 x 10-7 m to 7 x 10-7 m fall in the visible region.
The wavelength of the light of violet colour is the shortest, and that of red colour is the longest. Visible light is obtained from the glowing bodies, while they are white hot. The light obtained from the electric bulbs, sodium lamp, fluorescent tube is the visible light.
Thermal or Infrared Waves
They were discovered by Herchell in 1800. Their wavelength is of the order of 7 x 10-7 m to 10-3 m. A body on being heated, emits out the infrared waves. These radiations have the maximum heating effect. The glass absorbs these radiations, therefore for the study of these radiations, rock salt prism is used instead of a glass prism. These waves are mainly used for therapeutic purpose by the doctors, because of their heating effect.
Microwaves
They were discovered by Hertz in 1888. Their wavelength is in the range of nearly 10-4 m to m. These waves are produced by the spark discharge or magnetron valve. They are detected by the crystal or semiconductor detector. These waves are used mainly in radar and long distance communication.
Radiowaves
They were first discovered in 1895 by Marconi. Their wavelength is in the range of 0.1m to 105m. They can be obtained by the flow of high frequency alternating current in an electric conductor.
These waves are detected by the tank circuit in a radio receiver or transmitter.
Applications of Electromagnetic Spectrum
The different regions of the total electromagnetic spectrum have been put to the following uses
- Radiowaves are used in radar and radio broadcasting.
- Microwaves are used in long distance wireless communications via satellites.
- Infrared, visible and ultraviolet radiations are used to know the structure of molecules.
- Diffraction of X-rays by crystals, gives the details of the structure of crystals.
- The bones are opaque to X-rays but flesh is transparent. X-ray pictures of a human body are used in medical diagnosis of fractures and cracks of bones.
- The γ – rays are used in the study of the structure of the nuclei of atoms.