Q. A ray of light passes through an equilateral prism such that an angle of incidence is equal to the angle of emergence and the latter is equal to $\frac{3}{4}$ th the angle of prism. The angle of deviation is
A) $45{^\circ}$
B) $39{^\circ}$
C) $20{^\circ}$
D) $30{^\circ}$
Explanation
(d) Angle of incidence = angle of emergence
Ie, $i = i'$
Also, $i = \frac{3}{4} \times$ angle of equilateral prism = $\frac{3}{4} \times 60{^\circ} = 45{^\circ}$
Thus, angle of deviation
=$i + i - A$
=(45${^\circ} + 45{^\circ} - 60{^\circ}$) = 30${^\circ}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.