Electromagnetic Spectrum - العلم نور

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الجمعة، 12 أبريل 2019

Electromagnetic Spectrum



Electromagnetic Spectrum




Definition       
         The electromagnetic spectrum is a wide range of radiation frequencies and their respective wavelengths. The electromagnetic spectrum covers a wide range of frequencies ranging from less than 1 Hz to about 1025 Hz, these frequencies have respective wavelengths ranging from thousands of kilometers to atomic size.  

         There are separate bands within this frequency range each of them have electromagnetic waves within it, these electromagnetic waves have different names which are classified according to their frequencies and wavelengths (from the low-frequency or long wavelength to the high-frequency or short wavelength) as follows: radio waves, microwaves, terahertz waves, infrared, visible light, ultraviolet, X-rays, and gamma rays.


Types and uses of electromagnetic radiation

§  Radio waves.
         Antennas are used to emit and receive radio waves. This can be done by the usage of some conductors or by using transmitter which is used to generate an AC current for the application to an antenna. The radio communication systems such as television, mobile phones, satellites and wireless networking use radio waves to transmit information across distances.

§  Microwaves.
         We can say that microwaves are a specific type of radio waves which have short wavelengths (from 10 cm to 1 mm). klystron and magnetron are used to generate microwaves and short antennas are used to emit and absorb microwaves.
         The most famous application in which microwaves are used is microwave oven which is used for heating the food in our homes. Microwaves are also used in radar, satellites and wireless networking.

§   Terahertz Radiation.
         It's located in the electromagnetic spectrum between infrared and microwaves. Terahertz radiation has wavelengths of sub-millimeters which enable it to be used in communications, imaging and armed forces applications. Atmospheric gases are widely used to absorb terahertz radiation.

§  Infrared Radiation.
         It covers the range between 1 mm and 750 nm wavelengths within the electromagnetic spectrum. Infrared radiation is divided into 3 parts i.e. far-infrared, mid-infrared and near-infrared.
         Far-infrared has wavelengths between 1 mm to 10 μm. Phonons in solids in addition to molecular motion in liquids are used to absorb this type of radiation. It's used widely for astronomy.
         Mid-infrared has wavelengths between 10 μm to 2.5 μm. This type of radiation can be radiated by hot objects and also by human skin at normal temperature. Molecular vibrations are used to absorb this type of radiation.
         Near-infrared has wavelengths between 2.5 μm to 750 nm. The shortest wavelengths in this range of radiation can be detected by image sensors so it's used for infrared photography and videography.

§  Visible Radiation.
         It's the visible light which covers the range of wavelengths between 760 nm and 380 nm within the electromagnetic spectrum. This type of radiation is easily detected by the human eyes. It's a part of radiation which is emitted by the sun.

§  Ultraviolet radiation.
         It has wavelengths shorter than that of the violet part of visible light and longer than that of x-rays. The exposure to the middle range of UV radiation can cause skin cancer.

§  X-Rays.
         It's located between UV radiation and Gamma rays within the electromagnetic spectrum. It's can be emitted by black holes and some types of nebulae. X-rays are widely used in medical field for diagnostic imaging. They are also used in high-energy physics.

§  Gamma Rays.
         They were discovered in 1900 by Paul Villard. There's no defined lower limit to gamma rays' wavelengths. They have a wide range of applications in astronomy, physics and medicine. They are used widely for medical imaging, irradiation of foods and radiation cancer therapy.







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