A ray of light travelling through a rarer medium is incident at very small angle ' $i$ ' on a glass slab and…
A ray of light travelling through a rarer medium is incident at very small angle ' $i$ ' on a glass slab and after refraction its velocity is reduced by $25 \%$. The angle of deviation is
$\frac{3 \mathrm{i}}{4}$
$\frac{\mathrm{i}}{4}$
$\frac{\mathrm{i}}{3}$
$\frac{4 \mathrm{i}}{3}$.
Solution
$\begin{aligned} & n=\frac{\sin i}{\sin r}=\frac{i}{r} \quad \ldots(\because i \text { is very small, } \sin i \approx i) \\ & n=\frac{c}{v}=\frac{c}{0.75 c}=\frac{i}{r} \\ \therefore \quad r & =0.75 i=\frac{3}{4} i \\ \quad & \delta=i-r=i-\frac{3}{4} i=\frac{i}{4}\end{aligned}$