The Yerkes refracting telescope has a 1-m-diameter objective lens of focal length 20 m and an eyepiece of focal length 3.5 cm.What is the magnification of the planet Mars as seen through this telescope?
A)140
B)280
C)570
D)1,000
E)35

Question

The Yerkes refracting telescope has a 1-m-diameter objective lens of focal length 20 m and an eyepiece of focal length 3.5 cm.What is the magnification of the planet Mars as seen through this telescope?
A)140
B)280
C)570
D)1,000
E)​35

Quizplus · Accepted Answer

The magnification of the telescope is given by the ratio of the focal length of the objective lens to the focal length of the eyepiece, which is
M = - (f_obj / f_eyepiece)
where the negative sign is included to account for the inversion of the image. 
Substituting the given values, we get
M = - (20,000 cm / 3.5 cm) = -5,714.3
Since magnification is a relative quantity, we take the absolute value of the magnification to get
|M| = 5,714.3
Therefore, the magnification of the planet Mars as seen through this telescope is approximately 570. The answer is (C).

The Yerkes Refracting Telescope Has a 1-M-Diameter Objective Lens of Focal