A ray is incident normally on the face of an equilateral prism of refracting angle of 60°. The refractive index of the prism is $\frac{2}{\sqrt{3}}$. The angle of deviation will be:
Answer & explanation
Correct answer: option 2
The correct answer is Option (3) → 30°
Using Snell's law,
$μ\sin r = \sin e$
and, for an equilateral triangle,
$r_1+r_2=A$ $[r_1=0°]$
$⇒r_2=60°$
$∴\frac{2}{\sqrt{3}}\sin 60°=\sin e$
$\frac{2}{\sqrt{3}}×\frac{\sqrt{3}}{2}=\sin e⇒e=90°$
and,
Angle of deviation $(δ)=(i+e)-A$
$=(0+90)-60=30°$