If the tube length of an astronomical telescope is $105 \, cm$ and the magnifying power is $20$ for normal setting,calculate the focal length of the objective in $cm$.

Focal length of objective and eye piece of telescope are $200 \; cm$ and $4 \; cm$ respectively. What is the length of telescope for normal adjustment (in $; cm$)?

Write a note on Cassegrain telescope.

What is a telescope?

If the focal lengths of the objective and eyepiece of an astronomical telescope are $200 \, cm$ and $4 \, cm$ respectively,what will be the magnifying power for distant vision (normal adjustment)?

$A$ simple telescope consisting of an objective of focal length $60\,cm$ and a single eye-lens of focal length $5\,cm$ is focused on a distant object in such a way that parallel rays emerge from the eye-lens. If the object makes an angle of $2^o$ at the objective,the angular width of the image is.....$^o$