If light travels a distance $x$ in $t_1 \, s$ in air and $10x$ distance in $t_2 \, s$ in a medium,the critical angle of the medium will be

The phenomenon of reflection of radio waves by the ionosphere is similar to:

$A$ light wave enters from medium $1$ to medium $2$. Its velocity in the $2^{nd}$ medium is double that in the $1^{st}$ medium. For total internal reflection,the angle of incidence must be greater than.......$^o$.

What will be the minimum angle of incidence $i$ such that total internal reflection takes place at both interfaces (in $^{\circ}$)? (Given: $\mu_1 = \sqrt{2}, \mu_2 = 2, \mu_3 = \sqrt{3}$)

$A$ ray of light travelling in water is incident on its surface open to air. The angle of incidence is $\theta$,which is less than the critical angle. Then there will be

$A$ cylindrical transparent rod of refractive index $\mu = \frac{2}{\sqrt{3}}$ is surrounded by air. $A$ light ray is incident at the midpoint of one end of the rod as shown in the figure. The angle of incidence $\theta$ for which the light ray undergoes total internal reflection at the side wall of the rod is: