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 $17.0 \mathrm {~cm} .$ (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?
A) (a) 131 cm
$\quad$(b) 6.71
$\quad$(c) 0.15
B) (a) 97 cm
$\quad$(b) 0.15
$\quad$(c) 6.71
C) (a) 262 cm
$\quad$(b) 0.87
$\quad$(c) 1.15
D) (a) 194 cm
$\quad$(b) 1.18
$\quad$(c) 0.85

Question

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 $17.0 \mathrm {~cm} .$ (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?
A) (a) 131 cm 
$\quad$(b) 6.71
$\quad$(c) 0.15
B) (a) 97 cm 
$\quad$(b) 0.15
$\quad$(c) 6.71
C) (a) 262 cm 
$\quad$(b) 0.87
$\quad$(c) 1.15
D) (a) 194 cm
$\quad$(b) 1.18
$\quad$(c) 0.85

Quizplus · Accepted Answer

(a) The total length of the telescope is the sum of the focal lengths of the lenses. 
$L = f_\text{o} + f_\text{e} = 114\text{ cm} + 17.0\text{ cm} = 131\text{ cm}$ 
(b) The angular magnification of the telescope is given by $M = - \frac{f_\text{o}}{f_\text{e}}$. 
$M = - \frac{114\text{ cm}}{17.0\text{ cm}} = -6.71$ (Note that the negative sign indicates that the image is inverted.) 
(c) The magnification by turning the telescope around and looking through the objective lens first is given by $M' = \frac{f_\text{o}}{f_\text{e}}$. 
$M' = \frac{114\text{ cm}}{17.0\text{ cm}} = 6.71$

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 $114 \mathrm {~cm} \text {, }$