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.
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science