The focal length of the objective and eyepiece of a telescope are respectively $60 \, cm$ and $10 \, cm$. The magnitude of the magnifying power when the image is formed at infinity is:

Magnifying power of an astronomical telescope for normal adjustment is $10$ and the length of the telescope is $110 \ cm$. The magnifying power of the same telescope,when the image is formed at the near point,is:

$A$ reflecting telescope has a large mirror as its objective with a radius of curvature equal to $80 \, cm$. What is the magnifying power of this telescope if the eyepiece used has a focal length of $1.6 \, cm$?

$A$ 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?

In which type of telescope,an extra pair of inverting lens is available?

If the length of the tube of an astronomical telescope is $105 \, cm$ and its magnification power for normal adjustment is $20$,then the focal length of its objective lens will be ....... $cm$.