Four lenses of focal length $\pm 15\; cm$ and $\pm 150 \;cm$ are available for making a telescope. To produce the largest magnification,the focal length (in $cm$) of the eyepiece should be

An astronomical telescope has an eyepiece of focal length $5 \ cm$. The angular magnification in normal adjustment is $10$. When the final image is formed at the least distance of distinct vision $(25 \ cm)$ from the eyepiece,then the angular magnification will be:

$A$ small object is placed at a distance of $4 \,m$ from the objective of a telescope of focal length $2 \,m$. The focal length of the eyepiece is $0.2 \,m$. The final image of the object

The magnifying power of an astronomical telescope is $8$. If the distance between the two lenses is $54 \, cm$,find the focal lengths of the eyepiece and the objective lens.

An astronomical telescope has an objective and an eyepiece of focal lengths $40\, cm$ and $4\, cm$ respectively. To view an object $200\, cm$ away from the objective,the lenses must be separated by a distance of.....$cm$.

If the focal length of the eyepiece of a telescope is doubled, its magnifying power $(m)$ will be