Physics quiz question: telescope construction

Physics 205B Quiz 2, spring semester 2010
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 24.49(b)

Two converging lenses, with focal lengths of +90 cm and +1.5 cm, are to be used to make a telescope.

The _________ lens and the _________ lens should be used as the objective and the eyepiece, respectively, in order to make a telescope with the greatest amount of magnification.
(A) f = +1.5 cm; f = +90 cm.
(B) f = +90 cm; f = +1.5 cm.
(C) (The order of the lenses is not important.)
(D) (Not enough information is given.)

Correct answer (highlight to unhide): (B)

The angular magnification of the telescope using two converging lenses is given by:

M = –f_o/f_e,

such to obtain the greatest possible angular magnfication, the objective should be the longer focal length lens, and eyepiece should be shorter focal length lens.

Student responses
Section 31988
Exam code: quiz02L3n5
(A) : 1 student
(B) : 11 students
(C) : 0 students
(D) : 0 students

Success level: 91%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.20