The focal length of a convex mirror is $20\, cm$. Its radius of curvature will be.....$cm$.

If the distances of the object and its real image from the principal focus of a concave mirror are $16 \ cm$ and $9 \ cm$ respectively,then the focal length of the mirror is (in $cm$)

$A$ concave mirror has a focal length $20\,cm$. The distance between the two positions of the object for which the image size is double of the object size is......$cm$

$A$ convergent beam of light is incident on a convex mirror so as to converge to a distance $12 \, cm$ from the pole of the mirror. An inverted image of the same size is formed coincident with the virtual object. What is the focal length of the mirror? $(cm)$

Given a point source of light,which of the following can produce a parallel beam of light?

$A$ short linear object of length $l$ lies along the axis of a concave mirror of focal length $f$ at a distance $u$ from the pole of the mirror. The size of the image is approximately equal to