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Ultraviolet rays (UV-rays)
Explanation
1. Ultraviolet rays are electromagnetic waves of short wavelength ranging from nearly 10^-8 m to 3.9 ✕ 10^-7 m.
2. Their wavelengths are shorter than those of violet light.
3. They can be produced by the arcs of the mercury and iron. They can also be obtained by passing discharge through hydrogen and xenon.
4. The sun is the most important natural source of UV- rays.
5. UV- rays were discovered by Johann Wilhelm Ritter in 1801.
Properties
1. UV- rays can travel in vacuum with the speed of light.
2. They can undergo reflection, refraction, interference and polarization.
3. UV- rays can cause photoelectric effect.
4. They produce fluorescence in certain materials.
5. They cannot pass through glass but they can pass through quartz, fluorite, rock salts etc.
6. UV- rays possess the property of synthesizing vitamin D when the skin is exposed to sunlight.
Uses
1. UV- rays are used for checking the minerals samples.
2. They are used to study molecular structure.
3. UV- rays destroy bacteria and hence they are used for sterilizing surgical instruments.
4. Being invisible, UV- rays are used in burglar alarm.
5. They are used in high resolving power microscopes.
6. They are used to distinguish between real and false gems.
7. They are used in analysis of chemical compounds.
Visible light
Explanation
1. Visible rays are narrow part of electromagnetic spectrum which is detected by human eyes.
2. The wavelength range varies between 3.9 ✕10^-7 m to 7.5✕ 10^-7 m.
3. The frequency range of visible light is 8 ✕10^14 Hz to 4 ✕10^14 Hz.
4. Visible light is produced when excited atoms return to their normal states.
5. Visible light consists of different colours ranging from red to violet.
6. Different wavelengths give rise to different colors. The wavelength of red colour being largest while that of violet colour being least. The wavelength range of various parts of visible rays are as follows:
Infrared rays
Explanation
1. Infrared rays are electromagnetic waves which are responsible for heat radiation.
2. All hot bodies are sources of infrared rays.
3. The wavelengths ranges nearly from 4 ✕10^14 Hz to 3✕ 10^11 Hz
4. The frequency ranges from 4 ✕10^14 Hz to 3 ✕10^11 Hz.
5. About 60% of solar radiations are infrared in nature.
6. It was discovered by Sir Frederick William Hershell in 1800
Properties
1. Infrared rays obey laws of reflection and refraction.
2. They produce interference and polarization.
3. They affect the photographic plates.
4. When infrared rays are allowed to fall on the material surface, its temperature increases.
5. These rays are strongly absorbed by glass.
6. Thermocouple, thermopile, bolometer etc are used to detect infrared rays.
Uses
1. Infrared rays are used in long-distance Photography (photos taken in complete darkness).
2. They are used in diagnosis of superficial tumours and varicose veins.
3. They are used to cure infantile paralysis (polio) and to treat sprains, dislocations and fracture.
4. They are used in solar water heaters and solar cookers.
5. Used in medicine.
6. They use to keep green house warm.
7. They are used in remote controls of T.V., V.C.R., etc.
Microwaves
Explanation
1. Microwaves are electromagnetic waves of short wavelength ranging from nearly 1 ✕10^-4 m to 0.3 m.
2. Frequency range of microwaves is 5✕ 10^9 Hz to 10^12 Hz.
3. Microwaves are produced by special vacuum tubes called klystrons, magnetrons and Gunn diodes.
Properties
1. They obey the laws of reflection and refraction.
2. They travel in vacuum at the speed of light.
3. They heat an object on which they are incident.
4. Their absorption by water, fats, sugar, can produce heat.
5. They can penetrate haze, light rain and snow.
Uses
1. Microwaves are used in radar system for the location of the distant objects like ships, areoplanes,etc.
2. In wireless communications, long distance telephone communications system.
3. Satellite communications for T.V. broadcasting.
4. Microwaves oven are used for cooking.
5. For study of atomic and molecular structure.
Radio waves
Explanation
1. Radio waves are electromagnetic waves having a very long wavelengths ranging from about 10 centimeters to few hundred kilometres.
2. Radio waves are produced by oscillating electric circuits containing an inductor and a capacitor.
3. Radio waves have frequencies from 3kHz to 300GHz.
4. The frequency of the waves produced by thr circuits depends upon the magnitudes of the inductance and the capacitance.
Properties
1. They obey laws of reflection and refraction.
2. Radio waves get diffracted from the obstacles coming from their path. The size of the obstacles should be large as radio waves are having quite larger wavelengths.
3. They can penetrate throught rain, snow, clouds.
Uses
1. Radio waves are used for wireless communications purposes.
2. They are used for radio broadcasting and transmission of T.V. signals.
3. Cellular phones uses radio waves to transmit voice communications in the ultra high frequency (UHF) band.
4. Radio astronomy.
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