$A$ fish at a depth of $12 \, cm$ in water is viewed by an observer on the bank of a lake. To what height the image of the fish is raised? $....... \, cm$ (Refractive index of lake water $= 4/3$)

What is the time taken (in seconds) for light to cross a glass slab of thickness $4 \ mm$ and refractive index $\mu = 3$?

$A$ container is half-filled with a liquid of refractive index $\mu$. The other half is filled with an immiscible liquid of refractive index $1.5\mu$. If the apparent depth of the container is $1.5$ times the actual depth, find $\mu$.

$A$ small pin fixed on a table top is viewed from above from a distance of $50 \, cm$. By what distance would the pin appear to be raised if it is viewed from the same point through a $15 \, cm$ thick glass slab held parallel to the table? (Refractive index of glass $= 1.5$)

$A$ man standing in a swimming pool looks at a stone lying at the bottom. The depth of the swimming pool is $h$. At what distance from the surface of water is the image of the stone formed? (Line of vision is normal; Refractive index of water is $n$)

The observer at $O$ views two closely spaced spots on a vertical wall through an angled glass slab as shown. As seen by the observer,the spots appear