An astronomical refracting telescope is made from two lenses.The objective lens has a focal length of $114 \mathrm {~cm} \text {, }$ and the eyepiece lens has a focal length of $17.0 \mathrm {~cm} \text {. }$ (a)What is the total length of the telescope? (b)What is the angular magnification of the telescope?
(c)What is the magnification by turning the telescope around and looking through the objective lens first?

Question

Quizplus · Accepted Answer

(a) The total length of the telescope can be found by adding the focal lengths of the two lenses: 
Length = Objective lens focal length + eyepiece lens focal length 
Length = 114 cm + 17.0 cm = 131 cm

(b) The angular magnification of the telescope can be found using the formula: 
Magnification = (-) (focal length of objective lens)/(focal length of eyepiece lens)
Magnification = (-) (114 cm)/(17.0 cm) = (-) 6.71 
Note that the negative sign indicates that the image is inverted.

(c) When the telescope is turned around and the objective lens is used as an eyepiece, the magnification can be found using the formula: 
Magnification = (-) (focal length of eyepiece lens)/(focal length of objective lens)
Magnification = (-) (17.0 cm)/(114 cm) = (-) 0.15 
Note that the negative sign again indicates that the image is inverted.

An Astronomical Refracting Telescope Is Made from Two Lenses 114 cm, 114 \mathrm {~cm} \text {, }114 cm,

An Astronomical Refracting Telescope Is Made from Two Lenses $114 \mathrm {~cm} \text {, }$