Explain the working of an astronomical telescope using refraction of light.

Explanation

Astronomical telescopes are of two types:
i. Refracting telescopes
ii. Reflecting telescopes
Refracting telescopes:
i. The telescope which works on the refraction of light is refracting telescope.
ii. It consists of two convex lenses called objective (0) and eyepiece (E). The objective has large diameter and larger focal length. The eyepiece has shorter focal length and small diameter. These two lenses are mounted at the ends of hollow metallic tube such that, the distance between them can be adjusted.

iii. Light rays from distant object is incident on objective and forms an image AB.
iv. This image AB acts as an object for eyepiece, it is adjusted in such a way that final image is formed at the infinity.
v. To change the magnification, eye-pieces of different focal lengths can be used by keeping the objective same.