$A$ diminished virtual image can be formed only in

An object is placed in front of a concave mirror of focal length $f$. $A$ virtual image is formed with a magnification of $2$. To obtain a real image of the same magnification,the object has to be moved by a distance of:

$A$ 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 ..... .

The focal length of a concave mirror is $12\; cm$. Where should an object of length $4\; cm$ be placed,so that a real image of $1\; cm$ length is formed (in $; cm$)?

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

The focal length of a convex mirror is $20\, cm$. Its radius of curvature will be.....$cm$.