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

$A$ fish rising vertically at the rate of $3 \, m/s$ to the surface of water observes a bird above the water,diving vertically towards it at the rate of $9 \, m/s$. The refractive index of water is $4/3$. Calculate the actual velocity (velocity $w.r.t$ ground) of the bird in $m/s$.

The speed of light is maximum in

When a light ray enters a medium with refractive index $\mu$,it is observed that the angle of refraction is half the angle of incidence. The angle of incidence is .........

When a ray of light of frequency $6 \times 10^{14} \ Hz$ travels from water of refractive index $4/3$ to glass of refractive index $8/5$,its

$A$ mixture of a pure liquid and a solution in a long vertical column (i.e., horizontal dimensions << vertical dimensions) produces diffusion of solute particles and hence a refractive index gradient along the vertical dimension. $A$ ray of light entering the column at right angles to the vertical is deviated from its original path. Find the deviation in travelling a horizontal distance $d << h$, where $h$ is the height of the column.