A person is designing a telescope with a magnification of 10. If the telescope is limited to a length of 0.20 m, what is the approximate focal length of the objective?
A) 17 cm
B) 19 cm
C) 16 cm
D) 18 cm

Question

Quizplus · Accepted Answer

The magnification (M) of a telescope is given by the formula M = -f_o/f_e, where f_o is the focal length of the objective lens and f_e is the focal length of the eyepiece. The length of the telescope is approximately the sum of the focal lengths of the objective and the eyepiece, so L ≈ f_o + f_e. Given M = 10 and L = 0.20 m = 20 cm, we can set up the equations 10 = -f_o/f_e and f_o + f_e = 20. Solving these equations simultaneously, assuming a simple case where f_e is 2 cm (a common small focal length for an eyepiece), gives f_o = 20 - 2 = 18 cm.

A Person Is Designing a Telescope with a Magnification of 10