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......$cm$.

The focal length of the objective lens of a telescope is $30 \text{ cm}$ and that of its eye lens is $3 \text{ cm}$. It is focused on a scale at a distance $2 \text{ m}$ from it. The distance of the objective lens from the eye lens to see the clear image is: (in $\text{ cm}$)

The large aperture of an astronomical telescope is used to:

In a simple telescope,the focal length of the objective lens is $f_o = 60 \ cm$ and the focal length of the eyepiece is $f_e = 5 \ cm$. If the rays coming from the object make an angle of $2^\circ$ at the objective,then the angular magnification (angular size of the image) is ........... $^\circ$.

Where is the largest telescope in India? What is the diameter of the objective in it?

If an astronomical telescope has objective and eye-piece focal lengths of $200 \; cm$ and $4 \; cm$ respectively,then the magnifying power of the telescope for normal vision is: