An object is placed $40\;cm$ from a concave mirror of focal length $20\;cm.$ The image formed is

Assertion : The formula connecting $u, v$ and $f$ for a spherical mirror is valid only for mirrors whose sizes are very small compared to their radii of curvature.
Reason : Laws of reflection are strictly valid for plane surfaces,but not for large spherical surfaces.

The convergence of a concave mirror can be decreased by dipping it in which of the following?

$A$ point object is placed at a distance of $10 \ cm$ and its real image is formed at a distance of $20 \ cm$ from a concave mirror. If the object is moved by $0.1 \ cm$ towards the mirror,the image will shift by about:

$A$ concave mirror of focal length $60 \ cm$ forms a real image of size $5$ times the size of a real object. Find the distance between the mirror and the object. (in $cm$)

$A$ boy stands $30 \,cm$ in front of a mirror. The height of his erect image is $1/5 \,th$ of his actual height. The mirror used is ..... .