$A$ wide container is filled with water $\left(\mu=\frac{4}{3}\right)$ up to a height of $1 \ m$. Find the diameter of the disc at the top of the water surface from which light is coming out.

$A$ point source of light is placed at a depth $h = 0.5 \, m$ below the surface of a liquid $(\mu = \frac{5}{4})$. Then,the fraction of light energy that escapes directly from the liquid surface is:

The critical angle of light going from medium $A$ to medium $B$ is $\theta$. The speed of light in medium $A$ is $v$. The speed of light in medium $B$ is:

Assertion $(A)$: Propagation of light through an optical fibre is due to total internal reflection taking place at the core-clad interface.
Reason $(R)$: Refractive index of the material of the core of the optical fibre is greater than that of air.

One of the necessary conditions for total internal reflection to take place is ($i =$ angle of incidence,$i_{c} =$ critical angle).

The figure shows a transparent block of side lengths $a$ and $a$. The third dimension of the block is negligible. $A$ point source $S$,which can emit light in all directions,can move inside the block. It is desired that no light from $S$ should pass through the segment $AB$. The region in which $S$ must be present to satisfy this condition is shown by the shaded region. Choose the correct option.