Nature of light - Corpuscular theory of light - Wave theory of light

Nature of light

In those days scientists could explain light with some other light theories. We just know about the theory of light from the beginning search of nature of light.

Corpuscular theory of light

       The corpuscular theory was put forward by Sir Isaac Newton to account for the propagation of light energy through space. According to this theory a luminous body or source of light emits continuously, extremely tiny particles called corpuscles in all directions. These corpuscles travel in straight lines in space with enormous velocity. 

           These particles are so small that the luminous body does not suffer any loss of weight by emitting them even for a long time. Their mechanical impact on the retina of our eye produces the sensation of sight. On approaching the surfaces of material media their paths are modified depending on the nature of the medium. Differences in the size of corpuscles lead to the different colours produced by them.  Using this theory we can understand reflection and refraction also. 

            However, Foucault’s experiment showed that the velocity of light in water is less than that in air. This result was conclusive evidence against the corpuscular theory. Moreover, this theory was not able to explain the phenomena of interference, diffraction, and polarization of light.

Wave theory of light

The wave theory was put forward by Huygens. According to this theory, light is propagated as a wave motion from a luminous body in a medium called ether. 

           Light waves are transverse in nature. Every particle in the path of a light wave executes periodic vibrations about its position of equilibrium. A point source of light emits a wave that spreads out equally in all directions with the velocity of light. Such a disturbance is called a spherical wave. 

          Each particle in the path of a light wave being set into motion acts as a fresh source, giving rise to secondary waves. The envelope of these secondary waves after any interval gives the position of the wavefront at that instant. When the wavefront strikes the retina, the sensation of sight is produced.

There is a lot of confusion about light theory which is neither wave nor particle. But quantum theory reconciles the particle properties of light with the wave nature.