Question

An astronomical telescope and a Galilean telescope use identical objective lenses. They have the same magnification, when both are in normal adjustment. The eyepiece of the astronomical telescope has a focal length f. 

(a) The tube lengths of the two telescopes differ by f. 

(b) The tube lengths of the two telescopes differ by 2f. 

(c) The Galilean telescope has shorter tube length. 

(d) The Galilean telescope has longer tube length.

Answer 1

Correct Answer is: (b, c)

In normal adjustment, tube length of an astronomical telescope is (f_o + f_e) and that of a Galilean telescope is (f_o - f_e), where f_o and f_e are the focal lengths of the objective and the eyepiece respectively.

Here, f_e = f.

Magnification = f_o/f_e for both telescopes.