The ray I3P is incident at an angle greater than
the critical angle 'C' and hence it cannot emerge the rarer medium ( angle
of refraction would be > 900) ; such a ray is reflected back into the denser
medium ; obviously Ð I3P N' = Ð R3P N' .
Therefore the critical angle can also be defined as the minimum
angle of incidence in denser medium for which, total internal reflection
will take place.
Relation between Critical angle and Refractive Index (R.
For the ray I2P , i = c in denser medium 2 and the corresponding
refracted ray PR2
r = 900 in rarer medium = 1 (See Figure 10)