There is a small source of light at some depth below the surface of water (refractive index $= 4/3$) in a tank of large cross-sectional surface area. Neglecting any reflection from the bottom and absorption by water,the percentage of light that emerges out of the surface is (nearly) ..........$\%$. [Use the fact that the solid angle subtended by a cone of semi-vertical angle $\theta$ is $\Omega = 2\pi(1 - \cos\theta)$]

Two transparent media $A$ and $B$ are separated by a plane boundary. The speed of light in those media are $1.5 \times 10^{8} \ m/s$ and $2.0 \times 10^{8} \ m/s$,respectively. The critical angle for a ray of light for these two media is:

Explain the use of optical fibre in the medical field.

For a light ray to undergo total internal reflection, light must travel from $(i = \text{angle of incidence}, i_C = \text{critical angle})$

$A$ ray is incident on a prism $ABC$ and travels as shown in the figure. The minimum refractive index of the material of the prism should be .......

$A$ point source of light $S$ is placed at the bottom of a vessel containing a liquid of refractive index $\mu = 5/3$. $A$ person is viewing the source from above the surface. There is an opaque disc $D$ of radius $r = 1\, cm$ floating on the surface of the liquid. The centre of the disc lies vertically above the source $S$. The liquid from the vessel is gradually drained out through a tap. The maximum height $h$ of the liquid for which the source cannot be seen at all from above is: (in $, cm$)