In particular,
NM will be taken to be nearly equal to the length of the perpendicular
from the point N on the principal axis We have, for small angles,
tan ÐNOM = MN
OM
FIGURE 9 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