Browse by Stream
QnA
Home
QnA
Go To Your Study Dashboard

Get Answers to all your Questions

header-bg qa
  • Home
  • NCERT
  • A Cassegrain telescope uses two mirrors as shown in Fig. Such a telescope is built with the mirrors 20mm apart, If the radius of curvature of the large mirror is 220 mm and the small mirror is 140mm. where will the final image of an object at infinit be?

Q9.30  A Cassegrain telescope uses two mirrors as shown in Fig. 9.30. Such a telescope is built with the mirrors 20mm apart. If the radius of curvature of the large mirror is 220mm and the small mirror is 140mm, where will the final image of an object at infinity be?

            

            

 

 

Answers (1)

best_answer

Given,

Distance between the objective mirror and secondary mirror d= 20mm

The radius of curvature of the Objective Mirror 

 R_{objective}=220mm

So the focal length of the objective mirror

 f_{objective}=\frac{220}{2}=110mm

The radius of curvature of the secondary mirror   

R_{secondary}=140mm

so, the focal length of the secondary mirror

 f_{secondary}=\frac{140}{2}=70mm

The image of an object which is placed at infinity, in the objective mirror, will behave like a virtual object for the secondary mirror.

So, virtual object distance for the secondary mirror 

u_{secondary}=f_{objective}-d=110-20=90mm

Now, applying  the mirror formula in the secondary mirror:

\frac{1}{f}=\frac{1}{v}+\frac{1}{u}

\frac{1}{v}=\frac{1}{f}-\frac{1}{u}

\frac{1}{v}=\frac{1}{70}-\frac{1}{90}

v=315mm

Posted by

Pankaj Sanodiya

View full answer

Crack CUET with india's "Best Teachers"

  • HD Video Lectures
  • Unlimited Mock Tests
  • Faculty Support
cuet_ads

Similar Questions

Trending Articles/News

anam-khan

CBSE Date Sheet 2025 (Out) Live: Class 10, 12 board exam time table at cbse.gov.in; syllabus, sample papers
anam-khan

CBSE Class 12 board exam date sheet 2025 out; exams from February 15 to April 4
anam-khan

When will CBSE Board exam 2025 date sheet be released for Class 10, 12?

Latest Question