The velocity of light in a medium is $1.5 \times 10^8 \ m/s$. Its refractive index will be:

$A$ ray of white light is incident on a spherical water drop whose centre is $C$ as shown below. When observed from the opposite side,the emergent light

Monochromatic light is refracted from air into glass of refractive index $\mu$. The ratio of the wavelength of incident and refracted waves is

The refractive index of air with respect to vacuum is . . . . . . .

$A$ pole is vertically submerged in a swimming pool such that it casts a shadow of length $2.15 \, m$ within the water when sunlight is incident at an angle of $30^{\circ}$ with the water surface. If the swimming pool is filled to a height of $1.5 \, m$,then the height of the pole above the water surface in centimeters is $(\mu_W = 4/3) .........$

$A$ small coin is fixed at the centre of the base of an empty cylindrical steel container having radius $R=1 \,m$ and height $d=4 \,m$. At time $t=0$,the container starts getting filled with water at a flow rate of $Q=0.1 \,m^3/s$ without disturbing the coin. Find the approximate time $t$ in seconds when the coin will first be seen by the observer $O$ from a height of $H=5.75 \,m$ above and $L=1.5 \,m$ radially away from the coin as shown in the figure. (Take refractive index of water,$n=1.33$ or $4/3$)