i.e. ₁m₂ = Refractive index of medium 2 w.r.t. medium 1 =

Note :

(1) If we reverse the path of the light ray, i.e. take RP to be the incident ray from the denser medium 2 and PI to be the refracted ray in the rarer medium 1.

Critical Angle

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The ray of light entering the rarer medium from the denser medium bends away from the normal; i.e. angle of refraction (r) in rarer medium > angle of incidence (i) in denser medium. Therefore as shown in fig. 10, as i increases, r increases and since r > i; the ray I₂P incident at angle 'C' is just emerging out into the rarer medium and its path is parallel to the boundary. This angle 'C' is called the critical angle of the given denser medium in relation to the given rarer medium. The critical angle can be defined as the maximum angle of incidence possible in denser medium for the ray to just emerge out into rarer medium.

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