The minimum magnifying power of a telescope is $M$. If the focal length of its eye lens is halved, the magnifying power will become:

The magnifying power of a telescope is high if its objective and eyepiece have respectively

The objective and eyepiece of an astronomical telescope are double convex lenses with refractive index $1.5$. When the telescope is adjusted to infinity, the separation between the two lenses is $16 \,cm$. If the space between the lenses is now filled with water and the telescope is again adjusted for infinity, then the present separation between the lenses is: (in $\,cm$)

For large magnifying power of a telescope, which of the following conditions is required?

The final image formed by an astronomical telescope is

The focal length of an objective of a telescope is $3 \ m$ and its diameter is $15 \ cm$. Assuming that for a normal eye,the diameter of the pupil is $3 \ mm$ for its complete use,the focal length of the eyepiece must be: (in $cm$)