Question

An astronomical refractive telescope has an objective of focal length `20 m` and an eyepiece of focal length `2 cm`.
A. The length of the telescope tube is `20.02 m`.
B. The magnification is `1000`.
C. The image formed is inverted.
D. An objective of a larger aperture will increase the brightness and reduce chromatic aberration of the image.

Answer 1

Correct Answer - A::B::C
Here, `f_(0) = 20 m and f_(e) = 2 cm = 0.02 m`.
In normal adjustment, length of telescope tube `L = f_(0) + f_(e) = 20.02 m`
Magnification `= (f_(0))/(f_(e)) = (20)/(0.02) = 1000`.
The image formed is inverted (w.r.t. the object). Choice (a), (b) and (c ) are correct.