Q. The critical angle for refraction from medium 1 to air is θ1 and that from medium 2 to air is θ2 . If medium 2 is denser than medium 1. Find the critical angle for refraction from medium 2 to medium 1.

(a) sin^{-1} (sinθ_{2}/sinθ_{1} )

(b) sin^{-1} (sinθ_{1}/sinθ_{2} )

(c) sin^{-1} (sinθ_{2} )

(d) sin^{-1} (sinθ_{1} )

Ans: (a)

Sol:

sinθ_{1} = 1/μ_{1 }and sinθ_{2} = 1/μ_{2}

sinθ = 1/^{1}μ_{2} = μ_{1}/μ_{2} = sinθ_{2} / sinθ_{1}

θ=sin^{-1}(sinθ_{2} / sinθ_{1})