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The light from a… (Class 12 Physics SQP 2025-26, Q6)

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PhysicsCBSE Class 12 · Sample paper, session 2025-26 · 1 mark · MCQ

CBSE Class 12 Physics sample paper 2025-26: question 6

From the official CBSE sample question paper for 2025-26, section A, question 6, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q6 · 1 mark · MCQWave Optics

The light from a monochromatic source is incident on a single slit and the resulting diffraction pattern is viewed on a screen. The graph shows the variation of the intensity with the distance on the screen. The width of slit is increased keeping the intensity of the source the same. Which of the following graphs is correct? (The original curve is shown with a dashed line.)

  1. (A)Narrower central peak of same height as original
  2. (B)Broader, wider curve of same height
  3. (C)Broader and taller curve
  4. (D)Narrower and taller central peak

Figure in the paper: Graph of intensity vs distance showing single-slit diffraction pattern with central maximum and small side maxima; four option graphs compare a solid new curve with the dashed original. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

How does the width of the central maximum depend on the slit width ?

Hint 2

Does more light pass through a wider slit?

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. The angular half-width of the central maximum is , so a wider slit gives a narrower central peak.

  2. A wider slit also lets more light through and concentrates it into a smaller region, so the peak intensity increases. Option (D).

    1 mark

Answer: Option (D): narrower and taller central peak

Where the marks are

  • States that the width decreases () and the intensity increases (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Wave Optics, one at a time, marked against the answer key and marking points.Back to the full paperSample paper 2025-26: 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.