Reflection of Light

REFRACTION OF LIGHT

When a beam of light is travelling from one medium to another medium, a part of light gets reflected back into firstmedium at the inferface of two media and the remaining part travels throguh second medium in another direction. The change in the direction of light take place at the interface of two media.

Deviation or bending of light rays from their original path while passing from one medium to another is called refraction.
                    (or)
The phenomenon due to which light deviates from its initial path, while travelling from one optical medium to another optical medium is called refraction.

Refraction of light is due to change in speed of light as light passes from one medium to another medium.

In case of refraction of light frequency(colour) and phase do not change. But wavelength and velocity will change.
                     

i)Refracted ray: A ray of light which deviates from its path on entering in an another optical medium is called refracted ray.

ii) Angle of refraction(r): The angle which the refracted ray makes with normal, is called the angle of refraction.

iii) Angle of deviation due to refraction(\( \delta \)): It is the angle between the direction of incident light ray and refracted light ray.

iv) Emergent ray: A ray of light which emerges out from another optical medium as shown in the above figure is called emergent ray.

v) Angle of emergence (e): The angle which the emergent ray makes with the normal is called the angle of emergence.

Reflection of Light

II) Laws of Refraction

                 
        
i) Incident ray, refracted ray and normal always lie in the same plane.
ii) The product of refractive index and sine of angle of incidence at a point in a medium is constant.
    µ \(\times\) sini = constant
      \( \mu _1 \sin i_1 = \mu _2 \sin i_2 \)
    If \( i_1 = i \) and \( i_2 = r \) then  \( \mu _1 \sin i_1 = \mu _2 \sin r \) 
This law is called snell's law.

According to Snell's law,
       \( \frac{{\sin i}} {{\sin r}} \) =constant \( \left( { = \frac{{\mu _2 }} {{\mu _1 }}} \right) \)  for any pair of medium and for light of given wavelength.

Reflection of Light

III)When a light travels from optically rarer medium to optically denser medium obliquely

     

a)it bends towards normal.
b) angle of incidence is greater than angle of the refraction.
c) angle of deviation \(\delta\)=i-r.

Reflection of Light

IV) When a ray of light travels from optical denser medium to optical rarer medium obliquely
                   
a) it bends away from the normal at the point of incidence.
b) angle of refraction is greater than angle of incidence.
c) angle of deviation  \(\delta\)=r-i.

        

Reflection of Light

V) Condition for no refraction

i) When an incident ray strikes normally at the point of incidence, it does not deviates from its path. i.e., its suffers no deviation.
                     

In this case angle of incidence (i) and angle of refraction(r) are equal 
If the refractive indices of two media are equal
From snell's law,
µ sini =µ sin r,
sin i = sin r  ; \( \angle i = \angle r \)
Hence, the ray passes without any deviation at the boundary.

Note:
Because of the above reason a transperant solid is invisible in a liquid if their refractive indices are same.