CBSE Class 12-science Answered
Draw a ray diagram of astronomical telescope and derive the formula of its magnifying power when final image is formed at the least distance of distinct vision
Asked by Harshsharma245101 | 09 Oct, 2019, 08:05: PM
Expert Answer
Figure drawn above shows the ray diagram of astronomical telescope.
Parallel rays from distant object is focussed at focal point of objective lens and first image AB is formed.
Image AB is within the focal length of eye piece, hence it is magnified to form second image A'B'
at the distance of distinct vision D from eye.
Magnification of telescope is defined as the ratio of angle β subtended by first image with eye piece
to the angle α subtended by same image with objective lens.
If the angles are small, then we have, magnification m = ( β / α ) ≈ tanβ / tanα ..............(1)
In ΔABC, we have tanβ = (AB/BC) , In ΔABC' , we have tanα = (AB/BC')
Using the above tangents of angles, eqn.(1) is written as m = BC' / BC = fO / ue .................(2)
where fO is focal length of objective lens and ue is lens-to-object distance of eye piece.
Using lens equation, we have for eyepiece, (1/v) - (1/u) = 1/f
For the above lens equation, v = - D , u = - ue and f = fE , where fE is focal length of eyepiece.
hence, we get, -(1/D) + (1/ue ) = 1/fE ..................(3)
from (3), we get, ( fO / ue ) = ( fO / fE ) + ( fO / D ) = ( fO / fE ) [ 1 + ( fE / D ) ] ..................(4)
Hence using eqn.(2) and eqn.(4), we get magnification as, m = ( fO / fE ) [ 1 + ( fE / D ) ]
Answered by Thiyagarajan K | 09 Oct, 2019, 10:48: PM
Concept Videos
CBSE 12-science - Physics
Asked by mailtoanjalip2005 | 16 Mar, 2024, 08:22: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by divyanshsahu109 | 11 Mar, 2024, 05:57: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by am1954077 | 08 Mar, 2024, 04:57: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by himanshurawat5823 | 08 Mar, 2024, 01:24: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by rohandhawaniya17112006 | 06 Mar, 2024, 03:32: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by shivamtkr7767 | 03 Mar, 2024, 12:45: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by sahupranav2006 | 02 Mar, 2024, 03:37: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by rishabhverma895334 | 01 Mar, 2024, 07:24: AM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by writetoakashyadav | 28 Feb, 2024, 07:41: PM
ANSWERED BY EXPERT
CBSE 12-science - Physics
Asked by nikstar1456 | 14 Feb, 2024, 01:09: PM
ANSWERED BY EXPERT