Question

The Figure below shows a ray of monochromatic light LM incident on the first surface AB of a regular (equilateral) glass prism ABC. The emergent ray grazes the adjacent surface AC. Calculate the angle of incidence. (Refractive Index of glass = 1.5)

Answer 1

Given A = 60°, n = 1.5, At the surface AC, r₂ is the critical angle

∴

`sin r_2 = 1/n`

= `1/1.5`

= `2/3`

= 0.6667

∴ r₂ = sin^-1 (0.6667)

= 41.8°

Also, r₁ + r₂ = A

r₁ = A - r₂

= 60° - 41.8°

= 18.2°

At the surface AB,

`sini/(sinr_1) = n`

sin i = 1.5 × sin 18.2°

= 1.5 × 0.31

= 0.465

∴ i = sin^-1 (0.465)

= 27.7°