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 $cm$)

Write the relationship between the radius of curvature and the focal length for a spherical mirror.

The focal length of a concave mirror is $f$ and the distance from the object to the principal focus is $x$. The magnification will be:

The separation between the screen and a concave mirror is $2r$. An isotropic point source of light is placed exactly midway between the mirror and the screen. The mirror has a radius of curvature $r$ and reflects $100\%$ of the incident light. Find the ratio of illuminances on the screen with and without the mirror.

$A$ concave shaving mirror has a radius of curvature of $35.0 \, cm$. It is positioned so that the upright image of a man's face is $2.5 \, \times$ the size of the face. How far is the mirror from the face in $cm$?

$A$ concave mirror for face viewing has a focal length of $0.4\,m$. The distance at which you hold the mirror from your face in order to see your image upright with a magnification of $5$ is......$m$.