$A$ concave mirror of focal length $10 \, cm$ is immersed in water $(\mu = 4/3)$. The new focal length will be ...... $cm$.

$A$ virtual image three times the size of the object is obtained with a concave mirror of radius of curvature $36 \ cm$. The distance of the object from the mirror is ........ $cm$.

$A$ square of side $3 \ cm$ is placed at a distance of $25 \ cm$ from a concave mirror of focal length $10 \ cm$. The center of the square is on the axis of the mirror and the plane is perpendicular to the axis. The area enclosed by the image of the square is ........ $cm^2$.

The graph shows the variation of $v$ with change in $u$ for a mirror. Points plotted above the point $P$ on the curve are for values of $v$:

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

$A$ diminished virtual image can be formed only in