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

Answer: (D)

All of these

Answer 2

: In normal adjustment,

Length of telescope tube, $L = f_{o} + f_{e}$

Here,$f_{o} = 20mandf_{e} = 2cm = 0.02m$

$\therefore L = 20 + 0.02 = 20.02m$

and magnification, , $m = \frac{f_{o}}{f_{e}} = \frac{20}{0.02} = 1000$

The image formed is inverted with respect to the object.