The refractive index of a medium is $\frac{3}{2}$. The speed of light in this medium is . . . . . . $ms^{-1}$. (Speed of light in vacuum is $c = 3 \times 10^{8} \,ms^{-1}$)

$A$ beam of monochromatic blue light of wavelength $4200 \, \mathring{A}$ in air travels into water $(\mu = 4/3)$. Its wavelength in water will be.......$\mathring{A}$

$A$ ray of light is incident on a medium of refractive index $\mu$ at an angle of incidence $i$. On refraction in the medium,$\delta$ is the angle of deviation. Then:

Optical phenomena taking place for a mirror and a lens respectively are . . . . . . and . . . . . . .

$A$ 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

$A$ tank is filled with water to a height of $12.5 \;cm$. The apparent depth of a needle lying at the bottom of the tank is measured by a microscope to be $9.4 \;cm$. What is the refractive index of water?
If water is replaced by a liquid of refractive index $1.63$ up to the same height,by what distance would the microscope have to be moved to focus on the needle again?