$A$ concave mirror of focal length $f$ (in air) is immersed in water $(\mu = 4/3)$. The focal length of the mirror in water will be

What is linear magnification? Obtain the equation of linear magnification for a concave mirror.

The direction of a ray of light incident on a concave mirror is shown by $PQ$, where $PQ$ is parallel to the principal axis. The direction in which the ray would travel after reflection is shown by four rays marked as $A$, $B$, $C$ and $D$. Which of the four rays correctly shows the direction of the reflected ray?

The focal length of a concave mirror is $50 \ cm$. At what distance (in $cm$) should an object be placed to obtain a real and inverted image of double the size?

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 $; cm$)?

$A$ convex lens (of focal length $20\, cm$) and a concave mirror,having their principal axes along the same lines,are kept $80\, cm$ apart from each other. The concave mirror is to the right of the convex lens. When an object is kept at a distance of $30\, cm$ to the left of the convex lens,its image remains at the same position even if the concave mirror is removed. The maximum distance of the object for which this concave mirror,by itself,would produce a virtual image would be.....$cm$.