________________
other was that it was made of waves. A proper theory of the propagation of light did not come until 1865, when Maxwell succeeded in unifying the forces of electricity and magnetism. Maxwell's equations predicted that electomagnetic waves travel at a fixed speed. Thus, light is a rapidly alternating electromagnetic field travelling through space in the form of waves at a fixed speed.
In due course, it was established that radio-waves, light and X-ray are all waves forming the electromagnetic spectrum, a tiny fraction of which--the visible spectrum is visible in the form of light. This remained the accepted and proven theory of light upto 1905. Einstein's theory of light was that it is composed of tiny particles called photons. A beam of light is analogous to a stream of bullets. To prove his theory, Einstein referred to a phenomenon called the photo-electric effect, in which when light impinges on a metal surface, it sends electrons flying off. If a photon hits an electron, it knocks it away just as one billiard ball hitting another one knocks it away. It was also found that the velocity of the rebounding electrons did not depend upon the intensity of the impinging light, but on its
colour." Satish K. Gupta, op.cit., p. 739– “Human eye is sensitive to only visible part of the electromagnetic spectrum. Different types of detectors are used to detect and study the different parts of the spectrum The follwing table gives the wavelength range of different colours of visible light:
Visible Spectrum Colour Wavelength (m)
Colour
Wavelength (m) Violet 3.9 x 10-7-4.5 x 10-7 Yellow 5.7 x 10-75.9 x 10-7 Blue 4.5 x 10-2 - 5 x 10-7 Orange 5.9 x 10-7 - 6.2 x 10-7 Green 5 x 10-7- 5.7 x 107 | Red 6.2 x 10-7-7.8 x 10-2
53.
54
(a) Ibid., p. 736–
Hertzs Experiment "In 1865, Maxwell had predicted the propagation of electromagnetic waves in the form of varying electricand magnetic fields, which produce each other. It was concluded that the accelerated charges the source of electromagnetic waves. In 1887, Hertz experimentally demonstrated the production of electromag
98
C
J
TG 4511 310 120-121
Jain Education International
For Private & Personal Use Only
www.jainelibrary.org
