Question

Find the angle of incidence at which a ray of monochromatic light should be incident on the first surface AB of a regular glass prism ABC so that the emergent ray grazes the adjacent surface AC. (Refractive Index of glass = 1 .56)

Answer 1

Let i be the angle of incidence on the face AB so that the refracted ray is incidence on the face AC to emerge along the face AC.

Now, sin C = `1/mu = 1/1.56 = 0.6410`

∴ C = 39.87°

If r is the angle of refraction at the surface AB, then

r + C = 60°

r = 60° - 39.87° = 20.13°

Now, `mu = "sin i"/"sin r"`

or sin i = 1.56 ×  0.3442 = 0.5369

∴ i = 35.47°