The time required for light to pass through a glass slab of $2 \ mm$ thickness is $({\mu _{glass}} = 1.5)$.

Time taken by the sunlight to pass through a slab of $4 \ cm$ and refractive index $1.5$ is . . . . . . $s$.

$A$ glass slab of thickness $3 \ cm$ is placed on an ink mark on a piece of paper. For a person looking at the mark from a distance of $5.0 \ cm$ above the top surface of the slab, the mark appears to be at a distance of $4.0 \ cm$ from the observer. The refractive index of the slab is:

White light is incident normally on a glass slab. Inside the glass slab,

$A$ fish rising vertically upward with a uniform velocity of $8\,ms^{-1}$ observes that a bird is diving vertically downward towards the fish with a velocity of $12\,ms^{-1}$. If the refractive index of water is $\frac{4}{3}$,then the actual velocity of the diving bird to pick the fish will be $.......\,ms^{-1}$.

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