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56. (a) Text book of Physics (Part-II), p. 100 —
The Electromagnetic Spectrum After successful generation of electromagnetic waves by Hertz, scientists were convinced of the reality of electromagnetic waves, thus a study of the electromagnetic waves of different wavelengths began. The X rays discovered by Rontgen in 1898 were shown to be electromagnetic waves in 1906. Subsequently, the spectrum of electromagnetic waves has been studied over a range of wavelengths covering 10-8 meter on the short wave side to around 10-15 meter on the long wave over the entire region. Our vision is limited to a very small part of this spectrum covering the waves with wavelengths of 4000 X 8000 Å, which we recognize as visible light. Our eyes do not respond to the electromagnetic radiations
our side this range. (b) Modern's A.B.C. of Physics, by Satish K. Gupta, pp. 737, 738
Electromagnetic Spectrum 1. Gamma Rays - Highly energetic radiations.
X-rays have frequencies in the range 10-16 to 3 x 10 Hz. Xray possess a high penetrating power. Ultra-violet rays. Ultra-violet rays were discovered by Ritter in 1801. The ultra-violet rays are part of solar spectrum. They can be produced by the arcs of mercury and iron. They can also be obtained by passing discharge through hydrogen and xenon. The frequency of ultra-violet rays lies in the range of 8 x 10 to 1016 Hz. Visible light. It forms a very narrow part of the electromagnetic spectrum and its frequency ranges from 4x10 to 8 x 10 Hz. The visible light is emitted due to the atomic excitation. Human eye is sensitive to only visible part of the electromagnetic spectrum. Infra red rays. Infra-red rays were discovered by Herschell. Infra-red rays are heat radiation and therefore all hot bodies are the sources of infra-red rays. About 60% of the solar radiation is infra-red in nature. The frequency range of infra
red rays is 1013 - 4 x 104 Hz.
6. Microwaves. The microwaves are produced by oscillating der EU 37001 - mar, 2003
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