Wave Nature of Light:-

• The propagation of the waves bitween the medium is desined by the refractive index of the medium.
• The refractive index is defined as the ratio of velocity of light in vaccume to the velocity of light in the medium.
• It is a unit less and dimension less quantity hence, referred as index number.
• If a wave is tavelling from one medium to an other then it bends due to the change in medium and this phenomenon is known as reflaction of light i.e bending of light.

• Refrective Index(RI)= c/v
  • Where c= Velocity in vaccume , v= Velocity in medium
• The reflaction of light is defined by snell’s law:-

Case1:-   n1>n2
 Sin r = n1/n2 Sin i,    
         >1
 Sin r>Sin i  
 n1 Sini/k = n2 Sin r  
 < r > < i 
 If  a wave is travelling from deuser 
to rearer medium then it moves away 
from the normal. 

 Case 2:-    n1>n2 ,    i=ic,    r = 90 
 
Critical angle:-   Critical angle is the
 minimum angle of incidance at which 
the wave emerges parallel to the interface
 i.e. angle r =90
n1Sin i=n2Sin r
n1Sin ic=n2Sin r
i=ic, r=90, ic= Critical angle
n1Sinic=n2Sin90
n1Sinic=n2
Sinic=n2/n1
ic=Sin^-1(n2/n1),  i.e. ic<90

• If a wave is is launched at angle greater than crirtical angle then it will return back to the original medium with very high efficiency.
• Case 3:- Conditional for total internal reflaction:-
  1. The wave should travel from denser to rearer medium that is why in optical fiber the refactive index of the core is greater than the refractiove index of the cladding.
  2. The light should be launched at an angle greater than critical angle.