An amateur astronomer has a telescope with an objective lens that measures 20 cm in diameter and 100 cm in focal length.What focal length of eyepiece should he or she choose in order to obtain a magnification of 50× ("50 power")?
A) 0.5 cm
B) 0.4 cm
C) 2 cm
D) 5 cm

Question

Quizplus · Accepted Answer

The magnification of a telescope can be calculated by dividing the focal length of the objective lens by the focal length of the eyepiece. So, in this case, we want a magnification of 50×, which means:

Magnification = Focal length of objective lens / Focal length of eyepiece

50 = 100 cm / Focal length of eyepiece

Focal length of eyepiece = 100 cm / 50

Focal length of eyepiece = 2 cm

Therefore, the amateur astronomer should choose an eyepiece with a focal length of 2 cm.

An Amateur Astronomer Has a Telescope with an Objective Lens