Q. A transparent solid cylindrical rod has a refractive index of 2/√3. It is surrounded by air. A light ray is incident at the midpoint of one end of the rod as shown in the figure. The incident angle θ for which the light ray grazes along the wall of the rod is
(a) sin-1(√3/2)
(b) sin-1(2/√3)
(c) sin-1(1/√3)
(d) sin-1(1/2)
Ans:(C)
Sol:Applying Snell’s Law for Air & medium inside the cylinder
1× sinθ = (2/√3)×sinr
Sinr = (√3/2 )sinθ —-(i)
Again by applying snell’s law for medium inside cylinder & Air
(2/√3 )sin(90-r) = sin90
cosr = √3/2 => r = 30
From (i) sin30 = √3/2 sinθ
sinθ = 1/ √3 => θ= sin-1(1/√3 )