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. I)

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)

Index

Light

16.1 Laws of Reflection at plane surfaces
16.2 Mirrors
16.3 Laws of Refraction at plane surfaces, Refractive Index and Critical Angle
16.4 Refraction at curved spherical surfaces and Lens maker’s formula
16.5 Lenses
16.6 Refraction in Prisms, Prism Formula
16.7 Dispersion of Light, Angular Dispersion and Dispersive Power
16.8 Optical Instruments and Magnifying Power

Chapter 17