An object is placed at the principal focus of a convex mirror. The image will be at

What will be the height of the image when an object of height $2 \ mm$ is placed on the principal axis of a convex mirror (of radius of curvature $40 \ cm$) at a distance of $20 \ cm$ from the mirror?

The image formed by a concave mirror is

An image formed by a concave mirror of focal length $6 \, cm$ is $3$ times the size of the object. The distance of the object from the mirror is......$cm$.

An object of height $3.6 \ cm$ is placed normally on the principal axis of a concave mirror of radius of curvature $30 \ cm$. If the object is at a distance of $10 \ cm$ from the principal focus of the mirror, then the height of the real image formed due to 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......$cm$