>> Study Material >> IIT JEE Physics >> Ray Optics A prism has
two plane surfaces AB and AC inclined to each other as shown in
following figure. A is called the angle of prism or refracting
angle. (i) Refraction Through A A light ray striking at one face
of a triangular glass prism gets refracted twice and emerges out
from the other face as shown above. The angle between the
emergent and the incident rays is called the angle of deviation
(D). The angle between the two refracting faces involved is
called the refracting angle (A) of the prism. From AXY, we have:
A + (90° – r1) + (90° – r2) = 180° As r1 + r2 = A (i) Deviation
D = (i – r1) + (e – r2) D = (i + e) – (r1 + r2) D = i + e – A A
+ D = i + e (ii) We also have two equations from Snell's Law at
X & Y. (i) Angle of Deviation It can be easily seen that if we
reverse the emergent ray, it goes back along the same path. The
angles of incidence and emergence get interchanged but the angle
of deviation remains same. Hence the same angle of deviation D
is possibl