Refraction of Light

INTRODUCTION

When light  ray travels in a homogeneous medium, it follows a straight line path. But as light ray passes obliquely from one transparent medium to another, it deviates from its original path. This phenomenon is called refraction of light. The deviation of light "occurs because light travels at different speeds in different media. The medium in which the speed of light is less is called denser medium  while the medium in which the speed of light is more is called rarer medium . When light goes from one medium to another, the frequency of light does not change However, the velocity and wavelength of light change. 

REFRACTION OF LIGHT

The 'phenomenon of change in the path of light ray as it passes obliquely from one transparent medium to another is called refraction of light. 

§  When a ray of light goes from a rarer medium  to a denser medium, it bends towards the normal .

§  When a ray of light goes from a denser medium to a rarer medium, it bends away from the normal .

§  No refraction takes place if the ray enters from one medium to another normally .

During refraction some changes occurs :

 (i) When a light ray goes from one medium to another, the frequency of ray does not change. 

(ii) The speed of light ray  and wavelength of ray  change. 

(iii) The intensity of the refracted ray is less than that of the incident ray. It is because there is partial reflection and absorption of light at the surface. 

LAWS OF REFRACTION:

The phenomenon of refraction of light ray takes place according to the following two  laws: 

1. The incident ray, the normal at the point of incidence and the refracted ray all lie in the same plane. 

First law of refraction

2. The ratio of the sine of angle of incidence to the sine of angle of refraction is constant for the two medium.

Second law is known as Snell's law and holds good for all angles of incidence.

i.e  Angle of incidence and angle of refraction may be vary  but their ratio is always constant

Where  ' n ' is constant and called Refractive index  of second medium w.r.t  first medium.

Note : 

•  The medium having incident ray is called first medium .
• The medium having refracted ray is called second medium.