Optics is the wider branch of physics which deals with the study of behavior and properties of light, its interactions with material objects and particles, and also the design and construction of instruments related to light.

The major branches of optics are the Physical and the geometrical optics. The physical optics describes the nature and properties of light and the latter deals with the principles which governs the image forming properties of optical devices.

Optics is an important portion of school curriculum which starts from class 6th of CBSE and roars into Ray and Wave optics in class 12th.

The major properties which extends as laws are the reflection and refraction. The law of reflection, which states that the angle of incidence and angle of refraction are equal to each other, and the Snell’s law or law of refraction which states that the ratio of sine of angle of incidence to the sine of angle of refraction is a constant, find its significance as the two major and basic laws in optics.

There are several theories stating the nature of light and its composition.  The corpuscular theory of light states by Descartes in 1637 states that the light consists of small discrete particles called corpuscles which moves with a finite velocity in a straight line.

Later Isaac Newton the godfather in the theoretical approach towards optics, conceptualized the particle theory of light as the initial step towards the understanding of photon. As these doesn’t suffice to explain the properties such as refraction, diffraction, interference and polarization – which actually require an in-depth understanding of the wave theory of light by Christian Huygens.

Albert Einstein, one of the masterminds in the field of physics, in March 1905, put forward the idea of quantum theory of light which explains that the light exists as tiny packets or quanta of energy called by its founder as Photons. Later the breakthrough theory was put forward by he himself called the Special Theory of relativity, which proved that the matter and energy is linked with each other, and thus the famous relationship E=mc2.

Students learn the topic light with a simple definition – “light is a form of energy which enables us the sensation of vision”. But the approach towards the light from the normal viewpoint changes as the grades change.

The seven basic properties of light, reflection, refraction, diffraction, interference, polarization, dispersion and scattering, comes into the curriculum as the most important topics in class 12. For ease of learning, the basic explanations are given below.

Reflection of light

Reflection is the phenomenon in which light travelling in one medium, incident on the surface of another bounces back to the first medium. According to the laws of reflection

  1. The incident ray, the reflected ray and the normal to the surface at the point of incidence all lie on the same plane.
  2. The angle of incidence is always equal to the angle of reflection.

Refraction of light

Refraction is the phenomenon of light in which the speed of light changes as it travels from one medium to another and light ray bends.

  1. The incident ray, the refracted ray and the normal to the surface at the point of incidence all lie on the same plane.
  2. For the given pair of optical media and for the light of given wavelength, the ratio of the sine of the angle of incidence to the sine of the angle of refraction is always a constant, called the refractive index.

Diffraction of light

The phenomenon of bending of light around corners of small obstacles and hence it’s encroachment into the region of the geometrical shadow is called diffraction.

Interference of light

Interference is the phenomenon of modification or change in the intensity of light due to redistribution of light energy in the region of superposition of two or more light waves.

Polarisation of light

Light vibrates in all directions perpendicular to the propagation of light, which is called the unpolarised light. If the light is constrained to vibrate in only one particular plane, then the light is called polarised light. The phenomenon is called polarisation of light.

Dispersion of light

The splitting up of a white light into its constituent seven colours is called dispersion.

Scattering of light

The phenomenon of light in which the rays of light get deviated from the straight path on hitting an obstacle of size comparable to wavelength is called the scattering of light.

We will discuss about the various branches, devices and, higher education and job opportunities in the field of optics, in the next blog…