The critical angle for light ray going from medium-1 to medium-2 is $i_{c}$. What will be the speed of light in medium-2, if its value in medium-1 is u?

$\frac{u}{\sin i_c}$

The correct answer is Option (3) → $\frac{u}{\sin i_c}$

The refractive index (u) of a medium is related to the speed of light in the medium (v) by -

$u=\frac{c}{v}$

$∴u_1=\frac{c}{v_1}$ [Medium 1]

$u_2=\frac{c}{v_2}$ [Medium 2]

and,

$\sin i_c=\frac{u_2}{u_1}$ [$i_c$ = critical angle]

$\sin i_c=\frac{\frac{c}{v_2}}{\frac{c}{v_1}}=\frac{u}{v_2}$ [$v_1=u$]

$v_2=\frac{u}{\sin i_c}$$