Define the focal plane of a concave mirror.

$A$ candle flame of $3\, cm$ is placed at $3\, m$ from a wall. $A$ concave mirror is kept at a distance $x$ from the wall in such a way that the image of the flame on the wall is $9\, cm$. Then $x$ is......$cm$.

An image formed by a convex mirror of focal length $30 \ cm$ is one-fourth the size of the object. The distance of the object from the mirror is ...... $cm$.

$A$ point source is situated at a distance $x < f$ from the pole of a concave mirror of focal length $f$. At time $t = 0$,the point source starts moving away from the mirror with constant velocity. Which of the graphs below represents best the variation of image distance $|v|$ with the distance $x$ between the pole of the mirror and the source?

$A$ concave mirror has a focal length of $30 \, cm$. If the image formed is erect (virtual),at what distance from the mirror should an object be placed so that the image is three times the size of the object (in $, cm$)?

The distance of a real object from the focus of a convex mirror of radius of curvature $a$ is $b$. Then the distance of the image from the focus is