Light

Light is the form of electromagnetic radiation that is visible to the human eye, responsible for the sense of sight. The wavelength of visible light is in a range from about 380 or 400 nanometers to about 760 or 780 nm with a frequency range of about 405 THz to 790 THz. The term light often comprises the adjacent radiation regions of infrared (at lower frequencies) and ultraviolet (at higher), not visible to the human eye.Many theories regarding the nature of light have been proposed from time to time, in order to explain the observed properties of light. In the seventeenth century, two theories of light – (i) Newton’s corpuscular theory and (ii) Huygens wave more widely accepted than suffered from many drawbacks and led to conclusions which were contradictory to the experimental result. Therefore Newton’s theory was discarded in favor of Huygens theory.

Wave Theory of Light:

The wave theory of light was proposed in 1678 by a Dutch physicist, Christian Huygens. According to this theory, light is propagated in the form of waves. These waves are emitted by a source of light and travel with a uniform velocity in homogeneous medium. Different waves enter our eyes and we get the sensation of light. In order to explain the propagation of waves of light though vacuum, Huygens suggested the existence of a hypothetical medium call ‘Luminferous ether’, which is all pervading i.e. present Huygens, light travel through ether in the form of waves. All attempts do not exist. This is the main drawback of the wave theory. Nevertheless, the different phenomena in light such as refection, refraction, interference, diffraction etc. can be satisfactorily explained on the basis, interference, diffract in etc. can be satisfactorily expanded on the basis of Huygens wave theory.

The explanation of refraction of light on the basis of the wave theory leads to the conclusion that the velocity of light in a rare medium is greater than that in denser medium. On the contrary, the explanation on the basis of Newton’s corpuscular theory leads to the conclusion that the velocity of light in rarer medium is less that in a denser medium. Later on, when velocity of light in different media was experimentally determined, it was proved that the velocity of light in a rarer medium is greater than that in a denser medium. As the theoretical conclusion obtained from the wave theory was in perfect agreement with the experimental result, it was conclusively proved that Huygens wave theory was correct.