$A$ convex lens $T$ is used to form an image whose size is one-fourth that of the size of the object. Then the object distance is (in $f$)

The graph shows how the magnification $m$ produced by a convex thin lens varies with image distance $v$. What was the focal length of the used lens?

$A$ thin equiconvex glass lens of refractive index $1.5$ has a power of $5 \,D$. When the lens is immersed in a liquid of refractive index $\mu$, it acts as a divergent lens of focal length $100 \,cm$. The value of $\mu$ of the liquid is:

$A$ substance is behaving as a convex lens in air and a concave lens in water. What is its refractive index?

The focal length of a glass convex lens is $2 \, cm$. What will be its focal length in $cm$ when it is immersed in a liquid of refractive index $1.25$?

$A$ convex lens makes a real image $4 \, cm$ long on a screen. When the lens is shifted to a new position without disturbing the object,we again get a real image on the screen which is $16 \, cm$ tall. The length of the object must be.......$cm$