$A$ microscope is focussed on a coin lying at the bottom of a beaker. The microscope is now raised by $1 \,cm$. To what depth should water be poured into the beaker so that the coin is again in focus is ........ $cm$ (The refractive index of water is $\frac{4}{3}$ )

$A$ 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:

$A$ paraxial beam of light is converging towards a point $P$ on the screen. $A$ plane parallel sheet of glass of thickness $t$ and refractive index $\mu$ is introduced in the path of the beam. The convergence point is shifted by:

The figure shows a ray of light entering and passing through a dense glass slab and emerging from the other side. If the angle of incidence $i=60^{\circ}$, slab thickness $b=0.04 \text{ m}$, and the refractive index of glass $\mu=\sqrt{3}$, the parallel shift $d$ between the emerging and entering rays in $\text{mm}$ is:

Assume the situation shown in the figure. Water $(\mu_w = 4/3)$ is filled in a beaker up to a height of $10 \, cm$. $A$ plane mirror is fixed at a height of $5 \, cm$ above the water surface. The distance of the image of the object $O$ from the mirror is ...... $cm$.

$A$ vessel of depth $d$ is half filled with oil of refractive index $n_1$ and the other half is filled with water of refractive index $n_2$. The apparent depth of this vessel when viewed from above will be