When light of two colours $A$ and $B$ is passed through a plane boundary; $A$ is bent more than $B$. Which colour travels more slowly in the second medium?

$(a)$ What should be the position of the object,when a concave mirror is to be used $(i)$ as a shaving mirror,and $(ii)$ in torches producing a parallel beam of light? $(b)$ $A$ man standing in front of a mirror finds his image having a very small head and legs of normal size. What type of mirror is used in designing such a mirror?

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?

$(a)$ What is meant by refraction of light?
$(b)$ If on applying Cartesian sign convention for spherical lenses the image distance obtained is negative,state the significance of the negative sign.

$A$ concave mirror and a convex lens are held in water. What changes, if any, do you expect in their focal length?

If the absolute refractive indices of water and glass are $\frac{4}{3}$ and $\frac{3}{2}$ respectively,then what will be the ratio of the velocity of light in water to that of glass?