A ray of light incident on an equilateral glass prism of refractive index \( \mu=\sqrt{3} \), travels parallel to the base of the prism inside it. What is the angle of incidence for this ray?
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 60°
In an equilateral prism (\( A = 60^\circ \)) a ray travelling parallel to the base passes symmetrically through the prism, so the angle of refraction at the first face equals that at the second, \( r_1 = r_2 \). Since \( r_1 + r_2 = A \):
\( r_1 = \displaystyle\frac{A}{2} = 30^\circ \)
By Snell's law at the first face:
\( \sin i = \mu\sin r_1 = \sqrt{3}\sin30^\circ = \displaystyle\frac{\sqrt{3}}{2} \Rightarrow i = 60^\circ \)