Time taken by the sunlight to pass through a window of thickness $4 \, mm$ whose refractive index is $1.5$ is

The back surface of a glass slab (refractive index $n$ and thickness $t$) is polished to act as a mirror,as shown in the figure. $A$ laser beam is incident on it,which is partially reflected and partially refracted at the air-glass interface. The refracted part is fully reflected at the mirror surface. $A$ pattern of discrete spots of light is observed on a screen placed perpendicular to the glass surface. The spacing between the spots on the screen is:

Two immiscible liquids of refractive indices $\frac{8}{5}$ and $\frac{3}{2}$ respectively are put in a beaker as shown in the figure. The height of each column is $6 \,cm$. $A$ coin is placed at the bottom of the beaker. For near normal vision,the apparent depth of the coin is $\frac{\alpha}{4} \,cm$. The value of $\alpha$ is . . . . . . .

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 $\mu = 1.5$)

In the given diagram,the apparent velocity of a bird (coming toward a fish) as seen by the fish is $19 \, cm/s$. Find the actual velocity of the bird in $cm/s$.

$A$ light wave is incident normally on a glass slab of refractive index $1.5$. If $4\%$ of light gets reflected and the amplitude of the electric field of the incident light is $30\, V/m$,then the amplitude of the electric field for the wave propagating in the glass medium will be.......$ V/m$