Q. Focal length of objective and eyepiece of telescope are 200 cm and 4 cm respectively. What is length of telescope for normal adjustment?
A) 196 cm
B) 204 cm
C) 250 cm
D) 225 cm
Explanation
(b) In normal adjustment of telescope tube, final image is formed at infinity, ie, $u_{e} = f_{e}$
Hence, length of telescope tube
Here, $f_{0}$ = 100cm, $f_{e}$= 4 cm
$\therefore L = 200 + 4 = 204$ cm
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.