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

In a reflecting telescope,a secondary mirror is used to:

The focal length of the objective and the eyepiece of a telescope are $100\, cm$ and $5\, cm$ respectively. If the final image is formed at the least distance of distinct vision,the magnification of the telescope is:

$A$ small object is placed at a distance of $4 \,m$ from the objective of a telescope of focal length $2 \,m$. The focal length of the eyepiece is $0.2 \,m$. The final image of the object

The diameter of the moon is $3.5 \times 10^3 \, km$ and its distance from the Earth is $3.8 \times 10^5 \, km$. Find the angle subtended by the moon at the eye when viewed through a telescope. The focal length of the telescope's objective is $4 \, m$ and the focal length of the eyepiece is $10 \, cm$. The angle is .......... $^o$.

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