The electromagnetic waves have wavelengths ranging from 10-15 m to 108 m. Human eyes are sensitive to visible light having wavelengths ranging from 4000 A° to 8000 A°. The classification of electromagnetic waves is referred to as the electromagnetic spectrum. The electromagnetic waves in increasing order of wavelengths and decreasing frequencies are ( i ) g-rays, ( ii ) X-rays, ( iii ) ultraviolet rays, ( iv ) visible light, ( v ) infrared rays, ( vi ) microwaves, ( vii ) short radio waves and ( viii ) long radio waves. g-rays have wavelengths less than 1 A° whereas radio waves have wavelengths more than 1 m. There are no sharp boundaries dividing the various sections of the electromagnetic spectrum.
Electromagnetic radiation and Earth’s atmosphere: -Processes like reflection, refraction, polarization, dispersion and absorption take place when electromagnetic rays coming from the Sun pass through different media in Earth’s atmosphere and reach the surface of the Earth. The Earth’s atmosphere consists of Troposphere (upto about 15 km), Stratosphere (15 to 50 km), Mesosphere (50 to 80 km) and Thermosphere (80 to 110 km). The important points to be noted about the Earth’s atmosphere are:
( 1 ) The density of the atmosphere decreases as we go higher. There is no sharp boundary between the different layers.
( 2 ) In the uppermost layer ( i.e., ionosphere ) there is a small amount of free electrons and positive ions.
( 3 ) The layers other than the ionosphere are electrically neutral.
( 4 ) Water molecules are present mostly in the lowermost layer ( Troposphere ).
( 5 ) Ozone gas ( O3 ) is present at the height ranging between 30 to 50 km. The O3 molecules are produced by dissociation of O2 molecules.
( 6 ) The Earth’s atmosphere is bound to the Earth due to the gravitational field of the Earth.
Green house effect: -
Of all the wavelengths of the electromagnetic waves, Earth’s atmosphere is transparent to the visible light. The infrared radiations from the Sun are absorbed in the atmosphere. During the day time, the Earth’s surface and various objects get heated and emit infrared radiations which are absorbed by molecules like CO2, H2O and re-emitted to the surface of the Earth. Thus heat energy is trapped in the lower atmosphere and its temperature is maintained. This is known as the Green house effect. Infrared rays are known as heat rays as they are responsible for producing warmth experienced during night. Some pollutants also contribute to the green house effect. In the absence of the green house effect, the average temperature of the lower atmosphere would have been much less. The harmful ultraviolet radiations and all wavelengths less than 3000 A° get absorbed in the Ozone layer which acts as a protective layer for us. Certain gases like Chloro-Fluoro Carbons (CFCs) used in refrigerator cause damage to the Ozone layer.
Electromagnetic waves and communication : -
Electromagnetic waves have revolutionized the field of communication. Waves of different frequencies interact differently with different media on earth and hence are used for different types of communications. They are broadly known as radio waves.
Electromagnetic radiation and Earth’s atmosphere: -Processes like reflection, refraction, polarization, dispersion and absorption take place when electromagnetic rays coming from the Sun pass through different media in Earth’s atmosphere and reach the surface of the Earth. The Earth’s atmosphere consists of Troposphere (upto about 15 km), Stratosphere (15 to 50 km), Mesosphere (50 to 80 km) and Thermosphere (80 to 110 km). The important points to be noted about the Earth’s atmosphere are:
( 1 ) The density of the atmosphere decreases as we go higher. There is no sharp boundary between the different layers.
( 2 ) In the uppermost layer ( i.e., ionosphere ) there is a small amount of free electrons and positive ions.
( 3 ) The layers other than the ionosphere are electrically neutral.
( 4 ) Water molecules are present mostly in the lowermost layer ( Troposphere ).
( 5 ) Ozone gas ( O3 ) is present at the height ranging between 30 to 50 km. The O3 molecules are produced by dissociation of O2 molecules.
( 6 ) The Earth’s atmosphere is bound to the Earth due to the gravitational field of the Earth.
Green house effect: -
Of all the wavelengths of the electromagnetic waves, Earth’s atmosphere is transparent to the visible light. The infrared radiations from the Sun are absorbed in the atmosphere. During the day time, the Earth’s surface and various objects get heated and emit infrared radiations which are absorbed by molecules like CO2, H2O and re-emitted to the surface of the Earth. Thus heat energy is trapped in the lower atmosphere and its temperature is maintained. This is known as the Green house effect. Infrared rays are known as heat rays as they are responsible for producing warmth experienced during night. Some pollutants also contribute to the green house effect. In the absence of the green house effect, the average temperature of the lower atmosphere would have been much less. The harmful ultraviolet radiations and all wavelengths less than 3000 A° get absorbed in the Ozone layer which acts as a protective layer for us. Certain gases like Chloro-Fluoro Carbons (CFCs) used in refrigerator cause damage to the Ozone layer.
Electromagnetic waves and communication : -
Electromagnetic waves have revolutionized the field of communication. Waves of different frequencies interact differently with different media on earth and hence are used for different types of communications. They are broadly known as radio waves.
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