The time taken by sunlight to cross a $5 \,mm$ thick glass plate $(\mu = 3/2)$ is

$A$ fish and a bird are moving as shown in the figure. Find the velocity of the bird as observed by the fish.

$A$ monochromatic ray of light travels through a glass slab and a water column. The number of waves in a glass slab of thickness $4 \ cm$ is the same as in a water column of height $5 \ cm$. If the refractive index of glass is $\frac{5}{3}$,then the refractive index of water is:

$A$ beam of light composed of red and green rays is incident obliquely at a point on the face of a rectangular glass slab. When coming out on the opposite parallel face, the red and green rays emerge from

An ink mark is made on a piece of paper. $A$ glass slab of thickness $t$ is placed on it. The ink mark appears to be raised up through a distance $x$ when viewed at nearly normal incidence. If the refractive index of the material of the glass slab is $\mu$,then the thickness of the glass slab $t$ is given by:

Up to what height should we fill a glass of $21\, cm$ height so that it may appear half-filled? (Assume the refractive index of the liquid is $\mu = 1.5$)