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

$A$ square wire frame of side $3 \ cm$ is placed $25 \ cm$ away from a concave mirror of focal length $10 \ cm$. What is the area enclosed by the image of the wire? (The centre of the square wire is on the axis of the mirror and the plane is perpendicular to the principal axis).

$A$ square wire frame of side length $3.0 \, cm$ is placed $25 \, cm$ away from a concave mirror of focal length $10 \, cm$. The center of the wire frame is on the axis of the mirror,with two of its sides perpendicular to the axis. The area of the image will be $..... \, cm^2$.

$A$ square wire frame of side $3 \, cm$ is placed at a distance of $25 \, cm$ from a concave mirror of focal length $10 \, cm$. The area of the image is ........ $cm^2$.

The image of an extended object,placed perpendicular to the principal axis of a mirror,will be erect if:

$A$ person wants a real image of his own,$3$ times enlarged. Where should he stand in front of a concave mirror of radius of curvature $30 \ cm$ (in $cm$)?