Find the magnification for the lens. The focal length is $25 \; cm$.

$A$ magnifying glass is to be used at a fixed object distance of $1 \text{ inch}$. If it is to produce an erect image magnified $5$ times,its focal length should be ........ $\text{inch}$.

Two point sources $P$ and $Q$ are $24 \ cm$ apart. Where should a convex lens of focal length $9 \ cm$ be placed in between them so that the images of both sources are formed at the same place?

If the image of an object is at the focal point $f$ to the right side of a convex lens, the position of the object on the left of the lens is at

The graph between the lateral magnification $(m)$ produced by a lens and the distance of the image $(v)$ is given by

The distance between an object and the screen is $80 \, cm$. $A$ lens produces an image on the screen when the lens is placed at either of the positions $20 \, cm$ apart. The focal length of the lens is ....... $cm$.