$A$ telescope has an objective lens of focal length $200 \, cm$ and an eyepiece with focal length $2 \, cm$. If this telescope is used to see a $50 \, m$ tall building at a distance of $2 \, km$,what is the height of the image of the building formed by the objective lens in $cm$?

When the tube length of an astronomical telescope is increased,its magnifying power will .......

The focal lengths of the objective lens and the eye lens of a Galilean telescope are $30\, cm$ and $3.0\, cm$ respectively. The telescope produces a virtual,erect image of an object situated far away from it at the least distance of distinct vision from the eye lens. In this condition,the magnifying power of the Galilean telescope should be:

The aperture of a telescope is made large,because

To increase the magnifying power of a telescope ($f_o$ = focal length of the objective and $f_e$ = focal length of the eye lens):

Which are two main points important for an astronomical telescope?