The length of a telescope is 2.20 m and the focal length of the eyepiece is 1.9 cm.What is the focal length of the objective lens?
A)41 cm
B)45 cm
C)111 cm
D)218 cm
E)16 cm

Question

Quizplus · Accepted Answer

We can use the formula for the magnification of a telescope: 
magnification = focal length of the objective lens / focal length of the eyepiece
Since we have the length of the telescope, we can also use the formula for the total magnification: 
total magnification = length of telescope / focal length of the eyepiece
Setting these two formulas equal to each other, we get: 
focal length of the objective lens / (1.9 cm) = (2.20 m) / (1.9 cm)
Solving for the focal length of the objective lens, we get: 
focal length of the objective lens = (2.20 m) / (1.9 cm) * (100 cm/m) = 231.58 cm ≈ 218 cm (rounded to two significant figures)

The Length of a Telescope Is 2