Question

An astronomical refractive telescope has an objective of focal length 20 m and an eyepiece of focal length 2 cm. then

• A. the magnification is 1000
• B. the length of the telescope tube is 20.02 m
• C. the image formed is inverted
• D. all of these

Answer 1

The correct option is D all of these

Here, $f_0=20mand{f}_e=2cm=0.02m$ In normal adjustment, Length of telescope tube, $L=f_0+f_e=20+0.02=20.02m$
and magnification, $m=\frac{f_0}{f_e}=\frac{20}{0.02}=1000$
The image formed is inverted with respect to the object.