$A$ convex lens of focal length $12.5 \ cm$ is used as a simple microscope. When the image is formed at infinity,the magnification is . . . . . . . (Near point for normal vision is $25 \ cm$)

$A$ compound microscope consists of an eyepiece of focal length $6.25 \, cm$ and an objective lens of focal length $2.0 \, cm$,separated by a distance of $15 \, cm$. What is the magnifying power when the final image is formed at infinity?

$A$ card sheet divided into squares each of size $1\,mm^2$ is being viewed at a distance of $9\,cm$ through a magnifying glass (a converging lens of focal length $9\,cm$) held close to the eye. What is the angular magnification (magnifying power) of the lens?

$A$ compound microscope produces a magnification of $24$. The focal length of the eyepiece is $5 \ cm$. The final image is formed at the least distance of distinct vision. The magnification produced by the objective is

$A$ microscope consists of an objective of focal length $1.9 \,cm$ and an eyepiece of focal length $5 \,cm$. The two lenses are kept at a distance of $10.5 \,cm$. If the image is to be formed at the least distance of distinct vision, the distance at which the object is to be placed before the objective is (least distance of distinct vision is $25 \,cm$). (in $\,cm$)

What are the objective and the eye-piece in an optical instrument?