Optics

It is a branch of physics that deals with the study of optical phenomenon like reflection, refraction, dispersion, interference, diffraction, etc.

Furthermore, this branch is divided into two parts:

1. Ray optics
2. Wave or physical optics

Wave Optics

It is defined as the branch of optics that deals with the production, emission and propagation of light, its nature and the study of the phenomenon like interference, diffraction and polarization.

In the early times, scientists have made a discussion on the nature and propagation of light and proposed various theories. Some of them are as follows:

i. Newton’s Corpuscular Theory

According to this theory, Newton in 1678 proposed that light consists of very tiny particles called corpuscles. These particles are tiny, massless, elastic and travels in a straight line. They travel with speed of 3 x 10⁸ ms^-1. This theory successfully explained:

1. Rectilinear propagation of light
2. Reflection of light as the corpuscles bounce back when it strikes the reflecting surface.
3. Refraction of light because these corpuscles when travels from rarer to denser medium the particles in the denser medium pulls the particles with greater force. And they bend towards the normal.

This theory failed because:

1. It claimed that the velocity of light in denser medium is greater than rarer medium.
2. It could not explain the phenomenon of light like interference, diffraction, polarization, etc.

ii. Huygen’s Wave Theory

In 1690, a Dutch scientist Christian Huygen proposed a new theory of light on the basis of wave nature. According to this theory, light propagates from the source in the form of a wave where a medium is required for propagation. For the propagation in space, it was assumed that there is a highly dense, elastic medium called ether medium. This theory successful explained: