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Dr. Anil Kumar Jain
wave theory of light. Light was shown by Maxwell to be a component of the electromagnetic spectrum. Light travels in the form of waves. All these waves are electromagnetic in nature and have same spead ( = 3 x 1010 cm/sec. ) in free space.
Thus, the light is defined here as the radiations that can affect the eye which shows the relative eye sensitivity of an assumed standard observer to radiations of various wavelengths. The lower and upper limits of visible spectrum (wavelength ) are not well defined, but they are about 4300 Å and 6900 Å respectively ( 1 ) = 108 cm). The eye can detect radiation beyond these limits, if it is intense enough. In many experiments in physics, one can use photographic plates or light sensitive electronic detectors in place of human eyes.
Each wavelength of visible spectrum of the electromagnetic radiations corresponds to a definite colour. As this wavelength changes, the colour will also change. The lowest wavelength which one can see corresponds to violet colour and the maximum wavelength which one can see corresponds to red colour.
The normal white light from the sun contains the whole visible spectrum. When white light falls on any material object, it absorbs some of the radiations and reflects the rest. The reflected radiations when reach our eyes, we perceive the colour of that object corresponding to the wavelength of these radiations. Thus, when the light from the sun falls on the grass, it absorbs radiations of all wavelength except one representing green colour. Consequently, only radiation of wavelength representing green colour reaches our eyes. They stimulate the optic equipment and we see the grass as green.
It is obvious that the reflection of wavelength corresponding to green colour and absorption of the rest of the wavelengths by grass is due to its own specific structural properties. Thus, on the basis of scientific theory of colour, it becomes clear that the perception of grass as green or rose as red depends upon the fact as to which wavelength is reflected and not absorbed by the object, and this in turn, is decided by something inherent in the object-some structural peculiarity of the object itself.
We perceive the sense of colour, not only by the reflection of some particular wavelength by an object, but sometimes body itself radiates the light of some specific colour. As the temperature of a body is raised, first of all it emits infra-red radiation, then red light, then yellow light and finally white light. If we could obtain even higher temperature in the laboratory, we could make bodies blue hot as is
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