What is the diameter of the objective used in astronomical telescopes in present use (in $cm$)?

$A$ 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....$cm$

An object is clearly seen through an astronomical telescope of length $50 \ cm$. The focal lengths of its objective and eyepiece,respectively,can be

If the tube length of an astronomical telescope is $96 \ cm$ and the magnifying power is $15$ for normal setting,then the focal length of the objective is . . . . . . $cm$.

$A$ Cassegrain telescope uses two mirrors as shown in the figure. Such a telescope is built with the mirrors $20 \; mm$ apart. If the radius of curvature of the large mirror is $220 \; mm$ and the small mirror is $140 \; mm$,where will the final image of an object at infinity be?

The focal length of the objective and eyepiece of a telescope are respectively $200 \, cm$ and $5 \, cm$. The maximum magnifying power of the telescope will be