Question

Galileo's Telescope Galileo's first telescope used a convex objective lens with a focal length f=1.7m and a concave eyepiece, as shown in the figure. (Figure 1)When this telescope is focused on an infinitely distant object, and produces an infinitely distant image, its angular magnification is +3.0.

 

 

A. What is the focal length of the eyepiece? in cm

 

b. How far apart are the two lenses? 

 

Answer 1

Solution:

$$ \text { (a) } \begin{aligned} M_{\text {total }} &=-\frac{f_{\text {obj }}}{f_{\mathrm{e}}} \\ f_{\mathrm{e}} &=-\frac{f_{\text {obj }}}{M_{\text {total }}} \\ &=-\frac{1.7 \mathrm{~m}}{3.0} \\ &=-57 \mathrm{~cm} \end{aligned} $$

(b) \(L=f_{\text {obj }}+f_{\mathrm{e}}=1.7 \mathrm{~m}-0.57 \mathrm{~m}=1.1 \mathrm{~m}\)