A ray of light, incident on an equilateral prism $(\mu=\sqrt{3})$, moves parallel to the base line of the prism inside it. Find the angle of incidence for this ray.

CBSE Class 12 · 2012 · Geometrical OpticsShort Answer

A ray of light, incident on an equilateral prism

(μ = 3)

, moves parallel to the base line of the prism inside it. Find the angle of incidence for this ray.

Answer: $i = 6 0^{\circ}$ .

When the refracted ray is parallel to the base, the prism is in the \emph{minimum-deviation} position, so

r_{1} = r_{2} = \frac{A}{2} = \frac{6 0 ^{\circ}}{2} = 3 0^{\circ}

μ = \frac{sin i}{sin r} \Rightarrow sin i = μ sin r = 3 sin 3 0^{\circ} = \frac{3}{2}

i = 6 0^{\circ}

CBSE Class 12 Board · 2012 · Subjective