The focal length of a plane mirror is $.....$

$A$ $10 \, cm$ tall object is placed perpendicular to the principal axis of a convex lens of focal length $30 \, cm$. The distance of the object from the lens is $20 \, cm$. Find the $(i)$ position,$(ii)$ nature,and $(iii)$ size of the image formed.

Two plane mirrors are at right angles to each other. $A$ man stands between them and combs his hair with his right hand. In how many images will he be seen using his left hand?

What can be said about the magnification of an image formed by a convex mirror?

Which of the following can produce a magnification of $+5$ as well as $-5$?

Give the relationship of magnification with focal length of a spherical mirror.