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Geometrical Optics question

2022 · Q179
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Geometrical Optics question

2022 · Q179

NEETPhysicsGeometrical OpticsMCQ+4 / −1

An astronomical refracting telescope is being used by an observer to observe planets in normal adjustment. The focal lengths of the objective and eye piece used in the construction of the telescope are 20 m and 2 cm respectively. Consider the following statements about the telescope :

(a) The distance between the objective and eye piece is 20.02 m

(b) The magnification of the telescope is (−-−) 1000

(c) The image of the planet is erect and diminished

(d) The aperture of eye piece is smaller than that of objective

The correct statements are :

  1. A
    (a), (b) and (d)
  2. B
    (a), (b) and (c)
  3. C
    (b), (c) and (d)
  4. D
    (c), (d) and (a)
View written solutionFree

Correct answer: A

Given f0 = 20 m = 2000 cm, fe = 2 cm

$\bullet$ Distance between objective and eye piece

l = f0 + fe

= 20 m + 2 cm = 20.02 cm

$\bullet$ Magnification of telescope

$$m = - {{{f_0}} \over {{f_e}}} = - {{2000\,cm} \over {2\,cm}} = - 1000$$

$\bullet$ Image formed by telescope is inverted.

$\bullet$ Aperture of eye piece is smaller than that of objective.

So, statements (a), (b) and (c) are correct.

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