Light propagates faster through a Medium $\mathrm{A}$ than through another Medium $\mathrm{B}$. Which of the two media has a higher optical density?

Light propagates faster through a medium $\mathrm{A}$ than through another medium $\mathrm{B}$. State the condition under which no change in the direction of propagation of a light ray would take place when it passes from Medium A to Medium B.

Why does a pencil appear bent when it is partially  dipped in water?

Trace the path of rays in the following ray diagrams.

What kind of lens would form an inverted and magnified image of the object?

Draw labelled diagrams to illustrate the differences between the virtual images formed by using a concave lens.