Question

A wave has velocity $u$ in medium $P$ and velocity $2u$ in medium $Q.$ If the wave is refracted from medium $P$ to medium $Q$ at an angle of incidence $30^\circ ,$ then the angle of refraction will be

• A. $30^\circ $
• B. $45^\circ $
• C. $60^\circ $
• D. $90^\circ $

Answer 1

Answer: (D)

From Snell's law,
$\mu _{P} \, sin 30^{o} = \mu _{Q} sin r$
$sin r = \frac{\mu _{P}}{\mu _{Q}} sin 30^{o}$
as $\mu \propto \frac{1}{v}$
$sin r = \frac{2 u}{u} \frac{1}{2} = 1$
$r = 90^{o}$