Question

For the same angle of incidence, the angles of refraction in media P, Q, R and S are ${50}^o,{40}^o,{30}^o,{20}^o$, respectively. The speed of light is minimum in medium :

• A. P
• B. Q
• C. R
• D. S

Answer 1

Answer: (D)

S

Velocity of light in air is $c$

$\therefore$ Velocity of light in a medium, $v=\frac{c}{n}$ ..........(1)

where, $n$ is the refractive index of the medium

Also from Snell's law of refraction: $1\times sini=n\times sinr$

$⟹$ $n=\frac{sini}{sinr}$

Thus equation (1) becomes: $v=\frac{c\times sinr}{sini}$

$⟹$$v\propto sinr$$(\because i=constant)$

As for medium $S$, $r={20}^o$ which is minimum

$⟹v$ is minimum in medium $S$