ENTRODUCTION a. Fig. 8.1 shows the path of a ray through a prism, ABC. 7, is the angle of refraction for air/glass, e
is the angle of refraction for glass/air or the angle of emergence for the whole prism. D is angle
of deviation, i. e. the angle between the original and final directions of the ray, and A is the
refracting angle of the prism. The ray will always emerge from AC as far as lz is less than the
critical angle for glass ( 41.5° ). It has been found that a ray emerges from the face AC for angles
ly between 30° and 70°. For small angles of incidence e. g.4= 5, 10, 150, the ray does not
emerge from the face AC but through the face BC. For these small angles, the corresponding
value of lz are greater than the critical angle for glass, so the rays become totally internally
reflected, and emerge from the face, BC
b. The variables that can be measured are l, r, D, and e. Also, A, which does not vary can be traced
out and measured. The above, listed quantities are connected as follows: By principle of
reversibility of light, the point of minimum deviation occurs when the light passes symmetrically
through the prism. Let the angle of minimum deviation be D and the refracting angle of the
prism be A.
:: A=T + T2=2r (le. r =T2=T)
From Snell's law n =
8.2
Also D= (1-7)+(12-2)
Since i = 12 = i and 11 = 72 =r
D=21 - 27 = 21-A
D+A
i = = DIA
84
And r=4
Put equation 8.4 and 8.5 in equation 8.2, we have,​