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A telescope has an objective… (Class 12 Physics 2024, Q19)

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PhysicsCBSE Class 12 · Board exam 2024, set 55/5/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2024: question 19

Set in the CBSE Class 12 board exam of 2024, paper 55/5/1, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerRay Optics and Optical Instruments

A telescope has an objective lens of focal length 150 cm and an eyepiece of focal length 5 cm. Calculate its magnifying power in normal adjustment and the distance of the image formed by the objective.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/5/1.

Hints

Open one hint at a time and try again before the next.

Hint 1

In normal adjustment the final image is at infinity.

Hint 2

Where does a lens form the image of a very distant object?

Step-by-step solution

Each step shows the marks it earns, as an examiner would award them. Checked by an independent re-solve from the question paper.

  1. In normal adjustment, magnifying power
    .

    1 mark

  2. The object (a distant one) is effectively at infinity, .

    Lens formula for the objective: , so .

    Hence cm. The image is formed at the focus of the objective, 150 cm behind it.

    1 mark

Answer: Magnifying power = 30; image formed by the objective at 150 cm from it

Where the marks are

  • Magnifying power m = f_o/f_e = 30 (1 mark)
  • Image distance of the objective = 150 cm (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Ray Optics and Optical Instruments, one at a time, marked against the answer key and marking points.Back to the full paper2024 board paper, set 55/5/1: every question, by section.

The question is transcribed from the official paper; figures are described in words. The solution, hints and chapter tag are ours. Spotted an error? Write tosupport@questionbuddy.in.