Question

The refractive index of air with respect to glass is expressed as ${\displaystyle {}_g{\mu }_a=\frac{\sin i}{\sin r}}$.

1. Write down a similar expression for _aμ_g in terms of the angles i and r.
2. If angle r = 90°, what is the corresponding angle i called?
3. What is the physical significance of the angle i in part (b)? 

Answer 1

1. R.I of glass w.r.t. air ${\displaystyle ={}_a{\mu }_g=\frac{\sin i}{\sin r}}$
   ∠r is angle of incidence in air
   ∠i is angle of refraction in medium
2. When angle r = 90°
   ∴ sin 90° = 1 in air
   Angle i in medium is called the critical angle.
3. The significance of ∠i = i_c = critical angle is:
   

   The refractive index of the denser medium relative to the rarer medium can be computed using the critical angle value.