$A$ fish looking from within water sees the outside world through a circular horizon. If the fish is $\sqrt{7} \ cm$ below the surface of water,what will be the radius of the circular horizon in $cm$?

$PQR$ is a right-angled prism with other angles as $60^o$ and $30^o$. The refractive index of the prism is $1.5$. $PQ$ has a thin layer of liquid. Light falls normally on the face $PR$. For total internal reflection at the face $PQ$,the maximum refractive index of the liquid is

Show that for a material with refractive index $\mu \geqslant \sqrt{2}$,light incident at any angle shall be guided along a length perpendicular to the incident face.

$A$ light ray is incident from a medium of refractive index $2$ into a medium of refractive index $\sqrt{3}$. The critical angle is (in $^{\circ}$)

$A$ rectangular glass block is placed on a printed paper lying on a horizontal surface. Find the minimum refractive index of the glass for which the letters on the paper are not visible from any of the vertical sides of the block.

$A$ ray of light travels from a medium of refractive index $\mu$ to air. Its angle of incidence in the medium is $i$,measured from the normal to the boundary,and its angle of deviation is $\delta$. If $\delta$ is plotted against $i$,which of the following best represents the resulting curve?