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Define Magnifying Power of a Telescope. Write Its Expression. - Physics

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प्रश्न

Define magnifying power of a telescope. Write its expression.

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उत्तर

Magnifying power of a telescope is defined as the ratio of the angle subtended at the eye by the image formed at the least distance of distinct vision to the angle subtended at the eye by the object lying at infinity, when seen directly.

The formula for magnifying power is,

Magnifiying power,`M = - f_0/f_e  (1 + f_e/D)`

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2011-2012 (March) Delhi Set 1

संबंधित प्रश्न

Draw a schematic ray diagram of a reflecting telescope showing how rays coming from a distant object are received at the eyepiece.


  1. For the telescope is in normal adjustment (i.e., when the final image is at infinity)? what is the separation between the objective lens and the eyepiece?
  2. If this telescope is used to view a 100 m tall tower 3 km away, what is the height of the image of the tower formed by the objective lens?
  3. What is the height of the final image of the tower if it is formed at 25 cm?

You are given three lenses of power 0.5 D, 4 D, and 10 D to design a telescope.

1) Which lenses should be used as objective and eyepiece? Justify your answer.

2) Why is the aperture of the objective preferred to be large?


Define its magnifying power and write the expression for it?


The eyepiece of an astronomical telescope has a focal length of 10 cm. The telescope is focussed for normal vision of distant objects when the tube length is 1.0. m. Find the focal length of the objective and the magnifying power of the telescope.


A Galilean telescope is 27 cm long when focussed to form an image at infinity. If the objective has a focal length of 30 cm, what is the focal length of the eyepiece?


Draw a ray diagram of a refracting astronomical telescope when final image is formed at infinity. Also write the expression for its angular magnification (magnifying power).


With the help of a ray diagram explain the working of a reflecting telescope.


Draw a labelled ray diagram showing the image formation by a refracting telescope. Define its magnifying power.


Read the passage given below and answer the question that follows.

There are two types of optical instruments: Microscopes and Telescopes. Microscopes are used to magnify very tiny objects whereas telescopes are used to study distant objects. Both of them deploy convex lenses. In his telescope, Newton used a large parabolic mirror to collect light from the stars and reduce aberrations.
  1. Rohit observed the launch of Chandrayan 3 with the help of an optical instrument. Name the instrument used by him.
  2. State any one advantage of a reflecting telescope over a refracting telescope.
  3. Which instrument is used to study the structure of a virus?
  4. What is the ability of an optical instrument to form enlarged images called?
  5. What is the difference between a compound microscope and an astronomical telescope (refracting type), as far as their lenses are concerned?

Useful Constants & Relations:

1 Charge of a proton e 1.6 × 10-19 C
2 Speed of light in vacuum c 3 × 108 ms-1
    1 u = 931 MeV

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