Question

A prism ABC of angle 30° has its face AC silvered. A ray of light incident at an angle of 45° at the
face AB retraces its path after refraction at face AB and reflection at face AC. The refractive index of
the material of the prism is


1​

Answer 1

ANSWER

At the mirrored surface, light must fall normal to the surface to retrace its path.

Using geometry

(90°−r

1

)+90°+30°=180°

∴r

1

=30°

Now using Snell's law at refraction

1×sin45°=μ×sinr

1

∴μ=

2

1

×2=

2