Four lenses of focal length $+ 15\, cm, + 20\, cm, + 150\, cm$ and $+ 250\, cm$ are available for making an astronomical telescope. To produce the largest magnification,the focal length of the eye-piece should be.....$cm$

The focal length of the objective and eyepiece of a telescope are respectively $200 \, cm$ and $5 \, cm$. The maximum magnifying power of the telescope will be

$A$ 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?

In a laboratory,four convex lenses ${L_1}, {L_2}, {L_3},$ and ${L_4}$ of focal lengths $2 \ cm, 4 \ cm, 6 \ cm,$ and $8 \ cm$ respectively are available. Two of these lenses form a telescope of length $10 \ cm$ and magnifying power $4.$ The objective and eye lenses are:

Four convergent lenses have focal lengths $100 \, cm, 10 \, cm, 4 \, cm$ and $0.3 \, cm$. For a telescope with maximum possible magnification,we choose the lenses of focal length

The length of a telescope is $36 \, cm$. The focal lengths of its lenses can be