$A$ concave mirror gives an image three times as large as the object placed at a distance of $20\,cm$ from it. For the image to be real,the focal length should be........$cm$

$A$ point object is placed at a distance of $30 \, cm$ from a convex mirror of focal length $30 \, cm$. Where will the image be formed?

$A$ $4.5 \;cm$ needle is placed $12 \;cm$ away from a convex mirror of focal length $15 \;cm$. Give the location of the image and the magnification. Describe what happens as the needle is moved farther from the mirror.

$A$ convex mirror of focal length $10\,cm$ is shown in the figure. $A$ linear object $AB = 5\,cm$ is placed along the optical axis. Point $B$ is at a distance of $20\,cm$ from the pole of the mirror. Then,the size of the image of $AB$ will be:

$A$ ray of light is incident on a concave mirror. It is parallel to the principal axis and its height from the principal axis is equal to the focal length of the mirror. The ratio of the distance of point $B$ (where the reflected ray intersects the principal axis) to the distance of the focus from the centre of curvature is ($AB$ is the reflected ray).

An object is placed at a distance of $40 \ cm$ in front of a concave mirror of focal length $20 \ cm$. The image produced is