14 Light undergoes successive total
internal reflections as it moves through an
optical fibre Rationalised 2023-24
Ray Optics and
Optical Instruments
233
 EXAMPLE 9 5
tan ÐNCM = MN
MC
tan ÐNIM  = MN
MI
Now, for DNOC, i is the exterior angle Therefore, i
= ÐNOM + ÐNCM
i = MN
MN
OM
+MC
(9