Brief introduction to optics

Light is a from of energy stimulates the sensation of vision and makes us see objects around us. Light is emitted by bodies which are heated to very high temperature,such as glowing electric bulb,burning candles,sun,etc.Light can travel through vacuum, It does not require material medium to travel from one place to other.
When light falls on an object,it is party reflected. We see the objects only when the light reflected from the objects enters into our eyes. Regarding the nature of light,Newton put forward the corpuscular theory of light. According to this theory, light consists of tiny elastic particles called corpuscles. A light source emits such corpuscles in all directions when these cor pules strikes an objects, they are partly reflected and the reflected corpuscles enter into our eyes and we see the objects. On the basis of this theory, phenomena like rectilinear propagation,reflection and refraction of light can be explained. At about the same time Huygens proposed wave theory of light. According to this theory, light is propagated in the form of wave through either which was assumed to be present everywhere.This theory explain besides reflection, refraction of light other phenomena like interference,diffraction and polarisation of light. But because of newton's popularity at that time, his corpuscular theory prevailed, and the wave theory remained in the black ground for over a century.
Later, experiments on the measurements of the velocity of light in different media showed that the velocity of light in denser medium, like water or glass, is smaller than the velocity of light in air. According to Newton's corpuscular theory, the velocity of light in denser medium should be greater than that in rarer medium with these experimental results, wave theory of light become general acceptance from scientific communities.
Still latter, it was found that when light of suitable frequency is incident on certain metals, electrons are emitted. This phenomenon could be explained only by assuming that light is absorbed or emitted in the form of quantum of energy .Each quantum of energy is a packet of energy called photon .Photons behave as particles.