To produce a magnified erect image of a far object,along with a convex lens,we will require:

Four lenses of focal length $\pm 15\; cm$ and $\pm 150 \;cm$ are available for making a telescope. To produce the largest magnification,the focal length (in $cm$) of the eyepiece should be

The number of lenses in a terrestrial telescope is

For a distant object,the angular magnification of an astronomical telescope is $5$. The distance between the objective and the eyepiece is $36 \, cm$,and the final image is formed at infinity. What are the focal lengths of the objective $(f_o)$ and the eyepiece $(f_e)$?

$A$ distant hot air balloon subtends $0.25^o$ at the objective lens of an astronomical telescope. The image subtends $1.5^o$ at the eyepiece when viewed with a relaxed eye. The objective and eyepiece are in a $35 \ cm$ long tube. Find the focal length of the eyepiece lens in $cm$.

An observer looks at a tree of height $15 \ m$ with a telescope of magnifying power $10$. To him,the tree appears