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MCQEasyJEE 2023Optical Instruments (Microscope, Telescope)

JEE Physics 2023 Question with Solution

In a reflecting telescope, a secondary mirror is used to:

Options:

  • A

    Make chromatic aberration zero

  • B

    Reduce the problem of mechanical support

  • C

    Move the eyepiece outside the telescopic tube

  • D

    Remove spherical aberration

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: A reflecting telescope uses a secondary mirror.

Find: The purpose of the secondary mirror.

The secondary mirror in a reflecting telescope redirects the light path so that the image can be viewed conveniently.

Thus, it is used to move the eyepiece outside the telescopic tube.

Therefore, the correct option is C.

Common mistakes

  • Confusing the role of the secondary mirror with elimination of chromatic aberration. Chromatic aberration is absent in reflecting telescopes because mirrors are used instead of lenses, not because of the secondary mirror. Focus on the light-redirection function of the secondary mirror.

  • Assuming the secondary mirror removes spherical aberration. Spherical aberration depends on the shape of the primary mirror and optical design, not on the presence of the secondary mirror. Identify the secondary mirror as a component that redirects the formed image.

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