Cross-section view of a prism is the equilateral triangle $ABC$ shown in the figure. The minimum deviation is observed using this prism when the angle of incidence is equal to the prism angle. The time taken by light to travel from $P$ (midpoint of $BC$) to $A$ is ___________ $\times {10}^{-10} \mathrm{s}.$ (Given, speed of light in vacuum $=3\times {10}^8 \mathrm{m} {\mathrm{s}}^{-1}$ and $\cos 30°=\frac{\sqrt{3}}{2}$)

Region $\mathrm{I}$ and $\mathrm{II}$ are separated by a spherical surface of radius $25 \mathrm{cm}$. An object is kept in region $I$ at a distance of $40 \mathrm{cm}$ from the surface. The distance of
the image from the surface is:

A ray of light passes from a denser medium to a rarer medium at an angle of incidence $i.$ The reflected and refracted rays make an angle of $90°$ with each other. The angle of reflection and refraction are respectively $r$ and $r^{\text{'}}.$ The critical angle is given by,

A ray of light entering from air into a denser medium of refractive index $\frac{4}{3}$, as shown in figure.
The light ray suffers total internal reflection at the adjacent surface as shown. The maximum value of angle $\theta$ should be equal to: