An object is placed at a distance $u$ from a concave mirror of focal length $f$. $A$ real image is formed on a screen placed at a distance $v$ from the mirror. As $u$ changes,$v$ also changes. Which of the following graphs correctly represents the variation of $1/v$ with $1/u$?

An object $5 \ cm$ tall is placed $1 \ m$ from a concave spherical mirror which has a radius of curvature of $20 \ cm$. The size of the image is $...... \ cm$.

$A$ short straight object of height $100\, cm$ lies before the central axis of a spherical mirror whose focal length has absolute value $|f|=40\, cm$. The image of the object produced by the mirror is of height $25\, cm$ and has the same orientation as the object. One may conclude from the information:

$A$ thin cylindrical rod of length $10\,cm$ is placed horizontally on the principal axis of a concave mirror of focal length $20\,cm$. The rod is placed in such a way that the midpoint of the rod is at $40\,cm$ from the pole of the mirror. The length of the image formed by the mirror will be $\frac{x}{3}\,cm$. The value of $x$ is $............$.

$A$ person looks at the image of two parallel finite length lines $PQ$ and $RS$ in a convex mirror (see figure). Which of the following represents schematically the image correctly? Note: Letters $P, Q, R$ and $S$ are used only to denote the endpoints of the lines.

$A$ spherical mirror forms an erect image three times the linear size of the object. If the distance between the object and the image is $80 \, cm$,the focal length of the mirror is........$cm$.