If symmetrical biconcave thin lens is cut into two identical halves. They are placed in different ways as shown.

A narrow beam of white light goes through a slab having parallel faces.

By properly combining two prisms made of different materials, it is possible to

A flat mirror $M$ is arranged parallel to a wall $W$ at a distance $L$ from it as shown in the figure. The light produced by a point source $S$ kept on the wall is reflected by the mirror and produces a light patch on the wall. The mirror moves with velocity $v$ towards the wall.

A biconvex lens of refractive index $n_2$ is placed such that the refractive index of the surrounding media is as shown. Then the lens 

In the figure shown a point object $O$ is placed in the air on the principal axis. The radius of curvature of the spherical surface is $60 \mathrm{cm}$. If is the final image formed after all the refractions and reflections.

A particle is moving towards a fixed convex mirror. The image also moves. If $V_{\mathrm{i}}=$speed of image and $V_{\mathrm{O}}=$speed of the object, then