Question

A light is travelling from air into a medium. Velocity of light in a medium is reduced to $0.75$ times the velocity in air. Assume that angle of incidence '$i$' is very small, the deviation of the ray is

• A. $i$
• B. $\frac{i}{3}$
• C. $\frac{i}{4}$
• D. $\frac{3i}{4}$

Answer 1

The correct option is C $\frac{i}{4}$

Let speed of light in air be $c$.

Thus speed of light in medium $v=\frac{3}{4}c$

Using $c\sin r=v\sin i$

As $i$ and $r$ are very very small.

$\therefore$ $c\times r=\frac{3}{4}c\times i$

We get $r=\frac{3i}{4}$

Deviation of the ray $\delta =i-r$

$⟹$ $\delta =i-\frac{3i}{4}=\frac{i}{4}$