Which Chishti saint is famously associated with the phrase 'light of Delhi'?

Draw the ray diagram of an astronomical telescope when the final image is formed at infinity. Write the expression for the resolving power of the telescope.

A person who can see the object clearly at a distance of $10 \mathrm{cm}$, requires spectacles to be able to see clearly objects at a distance of $30 \mathrm{cm}$. What type of spectacles should he use? Find the focal length of the lens.

An astronomical telescope has an objective lens of focal length $20 \mathrm{m}$ and an eyepiece of focal length $1 \mathrm{cm}$. Find the angular magnification of the telescope.

Draw a labelled ray diagram of an astronomical telescope in the near point adjustment position.

A giant refracting telescope at an observatory has an objective lens of focal length $15 \mathrm{m}$ and an eyepiece of focal length $1.0 \mathrm{cm}$. If this telescope is used to view the Moon, find the diameter of the image of the Moon formed by the objective lens. The diameter of the Moon is $3.48\times {10}^6 \mathrm{m}$, and the radius of the lunar orbit is $3.8\times {10}^8 \mathrm{m}$.