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The above image is… (Class 10 Science SQP 2024-25, Q39)

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ScienceCBSE Class 10 · Sample paper, session 2024-25 · 4 marks · Case-based

CBSE Class 10 Science sample paper 2024-25: question 39

From the official CBSE sample question paper for 2024-25, section E, question 39, for 4 marks. Try it first; the hints and our step-by-step solution are below.

Q39 · 4 marks · Case-basedCompetency-basedLight – Reflection and Refraction

The above image is that of a reflecting telescope. Reflecting telescopes revolutionised our ways of looking into the sky. They employ mirrors to gather and focus light, rather than relying solely on lenses as in their refracting counterparts. These telescopes utilise precisely shaped and polished mirrors to capture incoming light and reflect it to a focal point, where it forms an image for observation.

  1. A

    What kind of image of the star is seen by the observer at the eyepiece?

    1 mark
  2. B

    What kind of mirror is used in this reflecting telescope?

    1 mark
  3. C

    Explain with reason what kind of optical device (type of lens or mirror) that is used at the eyepiece.

    2 marks

  4. OR

    D

    What is the role of the plane mirror in the telescope?

    2 marks

Figure in the paper: Light rays from a distant star travel to a curved mirror on the right, reflect to a small tilted plane mirror, which directs them down through a tube to a lens at the eyepiece. (Visually impaired version: Azim uses a reading glass to light fire. A. Which lens can be used? B. What property of the lens helps? C. List two more uses of this kind of lens. OR D. Explain with reason the condition under which the lens can form both real as well as virtual images.) See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

Which kind of mirror can bring parallel rays from a far-away star to a focus?

Hint 2

An eyepiece is used like a reading glass. Is the image you see through a reading glass real or virtual?

Hint 3

Without the small tilted mirror, where would the observer have to place their head to see the image?

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. A. The concave mirror first forms a real, inverted image of the star near its focus. The eyepiece lens then acts like a magnifying glass on this image.

    ½ mark

  2. The observer therefore sees a magnified, virtual image (inverted with respect to the star) through the eyepiece.

    ½ mark

  3. B. Light from a distant star arrives as parallel rays. These rays must be gathered and brought to a focus, which only a concave (converging) mirror can do. A concave mirror is therefore used.

    1 mark

  4. C. The eyepiece is a convex (converging) lens.

    1 mark

  5. Reason: It collects the rays reflected by the plane mirror. The image formed by the concave mirror lies within the focal length of this lens, so the lens forms an enlarged image that the eye can view comfortably, just as a reading glass magnifies an object.

    1 mark

  6. D. (Alternative to C) The plane mirror is set at an angle in the path of the rays converging from the concave mirror. It reflects these rays sideways out of the tube towards the eyepiece. The observer can then view the image without blocking the light entering the telescope.

    1 mark

  7. The plane mirror does not change the size of the image. It only shifts the position of the image formed by the curved mirror, and it laterally inverts that image.

    1 mark

Answer: A: a magnified virtual image (inverted w.r.t. the star); the intermediate image by the mirror is real; B: concave mirror; C: convex (converging) lens, which magnifies the image formed by the mirror; OR D: the plane mirror redirects the rays out of the tube to the eyepiece, shifting (and laterally inverting) the image

Where the marks are

  • A: Identifies the nature of the image seen at the eyepiece (1 mark)
  • B: Concave mirror (1 mark)
  • C: Converging/convex lens (1 mark)
  • C: Reason: collects the rays and magnifies the image formed by the mirror (1 mark)
  • OR D: Plane mirror reflects the converging rays towards the eyepiece (1 mark)
  • OR D: Shifts the position of the image and laterally inverts it (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Light – Reflection and Refraction, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2024-25: 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.