An astronomical telescope has an objective of focal length $100 \, cm$ and an eyepiece of focal length $5 \, cm$. The final image of a star is seen $25 \, cm$ from the eyepiece. The magnifying power of the telescope is ...........

$(a)$ $A$ giant refracting telescope at an observatory has an objective lens of focal length $15 \; m$. If an eyepiece of focal length $1.0 \; cm$ is used,what is the angular magnification of the telescope?
$(b)$ If this telescope is used to view the moon,what is the diameter of the image of the moon formed by the objective lens? The diameter of the moon is $3.48 \times 10^{6} \; m$,and the radius of the lunar orbit is $3.8 \times 10^{8} \; m$.

The number of lenses in a terrestrial telescope is

In a terrestrial telescope,the focal length of the objective is $90\, cm$,the inverting lens is $5\, cm$,and the eye lens is $6\, cm$. If the final image is formed at $30\, cm$ from the eye lens,calculate the magnification.

An object is clearly seen through an astronomical telescope of length $50 \ cm$. The focal lengths of its objective and eyepiece,respectively,can be

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