Physics - Geometrical Optics Question with Solution | TestHub

According to Snell's law, $\mu =\frac{\sin i}{\sin r}$

The refractive index is also given by $\mu =\frac{c}{v}$

Equating the two expressions, we get $\frac{c}{v}=\frac{\sin i}{\sin r}$

$v=c\frac{\sin r}{\sin i}$

For a given angle of incidence $i$, the speed of light $v$ is directly proportional to $\sin r$.

Since the sine function is increasing in the interval $(0^{\circ },90^{\circ })$, the minimum value of $r$ will result in the minimum speed of light.

The minimum angle of refraction is $20^{\circ }$, which corresponds to medium D.

Therefore, the speed of light is minimum in medium D.

Answer: D