How much water should be filled in a container $21 cm$ in height, so that it appears half filled when viewed from the top of the container? (given that $a \mu_\omega$ = 4/3)  

A fish is a little away below the surface of a table. If the critical angle is $49^o$, then the fish could see things above the water surface within an angular angle of

জলাশয়ের তলদেশ উহার প্রকৃত গভীরতার কতটুকু ? 

ABCD represents a glass slab and PQRS indicates the path of a light ray passing through the slab.If the refractive index of the glass is $\sqrt{3}$, find 'x'.

Three right angled prisms of refractive indices $\mu_1$, $\mu_2$ and $\mu_3$ are joined together ao that the faces of the middle prism are each in contact with one of the outside prisms. If the ray passes through the composite block undeviated, then