Question

In total internal reflection when the angle of incidence is equal to the critical angle what will be the refraction

Answer 1

f µd is the refractive index of the denser medium then, from Snell’s Law, the refractive index of air with respect to the denser medium is given by,

µa/ µd = sin i /sin r

1/ µd = sin i/sin r       (Since, µa = 1 for air)

If r = 90o, i = c

sin c/sin 90o = 1/µd  

Or, sin c = 1/µd

Or, c = sin-1(1/µd)

If the denser medium is glass, c = sin-1(1/µg)

Hence for total internal reflection to take place (i) light must travel from a denser medium to a rarer medium and (ii) the angle of incidence inside the denser medium must be greater than the critical angle i.e. i > c.