Two convex lenses of focal lengths $0.3 \, m$ and $0.05 \, m$ are used to make a telescope. The distance kept between the two is .... $m$

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 $\text{ cm}$)

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

The magnifying power of a refracting type of astronomical telescope is $m$. If the focal length of the eyepiece is doubled,then the magnifying power will become:

An astronomical refracting telescope is being used by an observer to observe planets in normal adjustment. The focal lengths of the objective and eyepiece used in the construction of the telescope are $20\,m$ and $2\,cm$ respectively. Consider the following statements about the telescope:
$(a)$ The distance between the objective and eyepiece is $20.02\,m$.
$(b)$ The magnification of the telescope is $1000$.
$(c)$ The image of the planet is erect and diminished.
$(d)$ The aperture of the eyepiece is smaller than that of the objective.
The correct statements are:

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......$cm$.