In this IIT JEE physic video lectures, we are going to discuss refraction. In the above physics video we are going to discuss the following the topics;

  • Laws of refraction
  • Snell’s law and refractive index
  • Absolute refractive index
  • Speed of light in different medium
  • And some exemplar problems

So let’s begin with the laws of refraction. The phenomenon of refraction is very interesting. Newton had explained refection. He told that the light is made up of various corpuscles and they travel at different speeds in different mediums. On the basis of this fact he described the laws of refraction. So what is the phenomenon of refraction? It occurs when a light ray crosses from one medium to other medium, the direction of light changes. It usually bends towards the normal to surface or away from the normal. Irrespective of the nature of the surface, the normal can be drawn. In the above video, there is diagrammatic representation of refraction a for better understanding of the topic. Moving on to Snell’s law and refractive index, the laws of refraction is,

For a particular media, Sine of angle of the angle of incident to sine of angle of refraction is constant.

The incoming ray, the normal to surface, the returning ray and the refracted all lay on the same plane.

According to the law of reversibility of light, we will get two angles between the two media. Further, in the video, in these physics lecture we have discussed an exemplary problem. Next, we have discussed Absolute refractive index. Refractive index is the ratio of the sine of angles between tow medium. If one of the media is air then the refractive index is known as an absolute refractive index. The absolute refractive index is always greater than 1, i.e. sin function of incident ray is greater than the Sin function of reflected ray. Now if we take two different media, then the refractive index is known as the relative refractive index.  It can be more or less than one. The last topic in this video is Speed of light in the different medium. The definition of the absolute refractive index can be given in terms of speed of light.  μ is Used to denote absolute refractive index.

And thus, μ= (speed of light in vacuum)/(speed of light in medium) = c/v

And thus,

v = c/μ , where

The value of speed of light in air 3X108 m/s. Different colour will have different frequencies. Taking λ as the wavelength we get c=vλ. The frequency of the light does not change as it moves from one medium to another. This is because; wavelength keeps changing as light moves from one medium to another.

μ=  λ/(ϑ/v)  = (wavelength of light in vacuum)/(wavelength of light in medium)

And in the end there is another problem.