In an astronomical telescope,the focal length of the objective lens is $100 \, cm$ and of the eyepiece is $2 \, cm$. The magnifying power of the telescope for the normal eye is:

The magnifying power of a telescope is $9.$ When it is adjusted for parallel rays,the distance between the objective and eyepiece is $20\; cm.$ The focal lengths of the lenses are:

An astronomical telescope has a large aperture to

When the diameter of the aperture of the objective of an astronomical telescope is increased,its

The focal length of the objective of a terrestrial telescope is $80 \, cm$ and it is adjusted for parallel rays. If its magnifying power is $20$ and the focal length of the erecting lens is $20 \, cm$,then the full length of the telescope will be......$cm$.

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