Which of the following ray diagrams is correct for the ray of light incident on a lens shown in the figure?

What is the power of a plane glass sheet?

Define absolute refractive index. Absolute refractive indices of medium $A$ and medium $B$ are $n_{a}$ and $n_{b}$ respectively. What is the refractive index of medium $B$ with respect to medium $A$? How does the velocity of light vary with change in the optical density of the media?

Which of the following can make a parallel beam of light when light from a point source is incident on it?

Two lenses have powers of $(a) +2 \text{ D}$ and $(b) -4 \text{ D}$. Find the nature and focal length of each lens.

The mirror outside the driver's side of a vehicle is usually a convex mirror. Printed on such a mirror is usually the warning "Vehicles in this mirror are closer than they appear". What is the reason for this warning?