What is the diameter of the objective used in astronomical telescopes in present use (in $cm$)?

$A$ planet is observed by an astronomical refracting telescope having an objective of focal length $16 \, m$ and an eye-piece of focal length $2 \, cm$. Which of the following statements is correct?

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:

What is a telescope? Discuss the types of telescopes that are used in general.

The objective lens of a telescope has a focal length of $100 \, cm$. When the final image is formed at the least distance of distinct vision,the distance between the lenses is $105 \, cm$. Calculate the focal length of the eyepiece in $cm$.

For an astronomical telescope,the focal length of the objective lens is $f_{0}$ and the eyepiece lens is $f_{e}$. Then the tube length of the telescope is . . . . . . .