The magnification power of a telescope is $9$ and the distance between the two lenses is $20 \, cm$. What are the focal lengths of the component lenses?

The aperture of a telescope is made large,because

$A$ Galileo telescope has an objective of focal length $100\,cm$ and magnifying power $50$. The distance between the two lenses in normal adjustment will be......$cm$

$A$ terrestrial telescope is made by introducing an erecting lens of focal length $f$ between the objective and eyepiece lenses of an astronomical telescope. This causes the length of the telescope tube to increase by an amount equal to

If both the object and the image are at infinite distances from a refracting telescope,its magnifying power will be equal to:

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.....$cm$.