Two plane mirrors are inclined at $70°$. A ray incident on one mirror at angle $\theta$ after reflection falls on the second mirror and is reflected from there parallel to the first mirror. $\theta$ is:

In the given figure, velocity of image with respect to mirror is

$AB$ is an incident beam of light and $CD$ is a reflected beam (the number of reflections for this may be $1$ or more than $1$) of light. $AB$ and $CD$ are separated by some distance (may be large). It is possible by placing what type of mirror on the right side?

A square $ABCD$ of side $1 \mathrm{mm}$ is kept at distance $15 \mathrm{cm}$ in front of the concave mirror as shown in the figure. The focal length of the mirror is $10 \mathrm{cm}$. The length of the perimeter of its image will be: