Given a point source of light,which of the following can produce a parallel beam of light?

Distance between an object and its three times magnified real image is $40 \ cm$. The focal length of the mirror used is . . . . . . $cm$.

Assertion $(A):$ The relation among $u, v$ and $f$ for a spherical mirror is valid only for mirrors whose sizes are very small compared to their radii of curvature.
Reason $(R):$ The laws of reflection are strictly valid for plane surfaces but not for large spherical surfaces.

An object is placed at $20 \ cm$ in front of a concave mirror,which produces a three times magnified real image. What is the focal length of the concave mirror (in $cm$)?

$A$ point object is placed at a distance of $30 \, cm$ from a convex mirror of focal length $30 \, cm$. The image will form at

$A$ 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 ........ $cm^2$.