The length of the telescope is 1.60 m and it has a magnification of 60.0. What is the focal length of the objective?
A) 60.0 cm
B) 157 cm
C) 100 cm
D) 128 cm
E) 96.0 cm

Question

Quizplus · Accepted Answer

Magnification = focal length of objective / focal length of eyepiece
Given magnification = 60
Length of telescope = focal length of objective + focal length of eyepiece
Length of telescope = 1.60 m = 160 cm
Let the focal length of eyepiece be fe
160 cm = fo + fe
fo = 160 - fe
Substituting in the magnification formula,
60 = fo / fe
60 = (160 - fe) / fe
60fe = 160 - fe
61fe = 160
fe = 2.62 cm
Substituting back in the equation 160 = fo + fe,
fo = 157.4 cm
Therefore, the focal length of the objective is 157 cm (option B).

The Length of the Telescope Is 1