Focal length of a convex lens is $20 \ cm$ and its refractive index is $1.5$. It produces an erect,enlarged image if the distance of the object from the lens is: (in $cm$)

The ray diagram shown could be correct:

The converging or diverging ability of a lens or mirror is called

The focal length of a convex lens of refractive index $1.5$ is $2 \ cm$. What will be the focal length of the lens when it is immersed in a liquid of refractive index $1.25$?

The power (in diopters) of an equiconvex lens with radii of curvature of $10 \ cm$ and refractive index of $1.6$ is

An object is placed at a distance $x$ from the focus of a convex lens,and its image is formed at a distance $x'$ from the other focus,as shown in the figure. Which relation do the distances $x$ and $x'$ satisfy?