An observer looks at a distant tree of height $10 \ m$ with a telescope of magnifying power of $20$. To the observer,the tree appears:

The length of an astronomical telescope for normal vision (relaxed eye) ($f_o$ = focal length of objective lens and $f_e$ = focal length of eye lens) is

The diameter of the moon is $3.5 \times 10^{3} \, km$ and its distance from the Earth is $3.8 \times 10^{5} \, km$. It is viewed by a telescope with objective and eyepiece focal lengths of $4 \, m$ and $10 \, cm$ respectively. What is the angular diameter of the image of the moon in degrees?

The magnifying power of a telescope with tube length $60 \; cm$ is $5$. What is the focal length of its eyepiece in $cm$?

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

The focal lengths of the objective and eye-piece of a telescope are $100 \ cm$ and $2 \ cm$ respectively. The moon subtends an angle of $0.5^o$ at the eye. If it is viewed through the telescope, the angle subtended by the moon's image will be......$^o$.