The refractive index of air with respect to glass is expressed as

${}_g{\mu }_a=\frac{\sin i}{\sin r}$.

Write down a similar expression for ${}_a{\mu }_g$ in terms of the angles $i$ and $r$.

The refractive index of air with respect to glass is expressed as ${}_{\mathrm{g}}\mathrm{\mu }_{\mathrm{a}}= \frac{\sin \mathrm{i}}{\sin \mathrm{r}}$ . If angle r is given as$90°$, then find that what the corresponding angle$\mathrm{i}$called and it will be equal to what?

The given figure shows a point source P inside a water container three rays A, B and C starting from the source P are shown up to the water surface. Show in the diagram the path of these rays after striking the water. The critical angle for water-air surface is $48°$. 

The given figure shows a point source P inside a water container three rays A, B and C starting from the source P are shown up to the water surface. Name the phenomenon which the rays A, B and C exhibit.

In the given figure PQ and PR are the two light rays emerging from an object P. The ray PQ is refracted as QS. State the special name given to the angle of incidence $\angle \mathrm{PQN}$of the ray PQ.

In the given figure below PQ and PR are the two light rays emerging from an object P. The ray PQ is refracted as QS. What is the angle of refraction for the refracted ray QS?

In the given figure PQ and PR are the two light rays emerging from an object P. The ray PQ is refracted as QS. Name the phenomenon that occurs if the angle of incidence$\angle PQN$ is increased.

In the given figure PQ and PR are the two light rays emerging from an object P. The ray PQ is refracted as QS. The ray PR suffers partial reflection and refraction on the water-air surface. Give reason. Draw in the diagram the refracted ray for the incident ray PR and hence show the position of image of the object P by the letter P’ when seen vertically from above.