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Answer the following. (Science 2026 31/4/1 Q35)

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ScienceCBSE Class 10 · Board exam 2026, set 31/4/1 · 3 marks · Short answer

CBSE Class 10 Science 2026: question 35

Set in the CBSE Class 10 board exam of 2026, paper 31/4/1, section C, question 35, for 3 marks. Try it first; the hints and our step-by-step solution are below.

Q35 · 3 marks · Short answerCompetency-basedLight – Reflection and Refraction

Answer the following.

  1. (a)

    Observe the given ray diagram and compare: (i) the speed of light in medium A and the speed of light in medium B. (ii) the optical densities of medium B and medium C.

    0 marks
  2. (b)

    Draw a ray diagram for refraction where the optical density of medium 'A' becomes equal to the optical density of medium 'C' and optical density of medium 'B' is greater than the optical density of medium 'A' and medium 'C'.

    0 marks

Figure in the paper: A ray of light travels from Medium 'A' (top) into Medium 'B' (a rectangular block) and then into Medium 'C' (below). The normal N is drawn at the upper surface, with angle i marked between the incident ray and the normal and angle r marked between the refracted ray and the normal. The ray bends towards the normal on entering Medium B and bends away from the normal on leaving it into Medium C. See it in the official paper.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 31/4/1.

Hints

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

Hint 1

Check whether the ray bends towards or away from the normal at each surface.

Hint 2

Bending towards the normal means the light has entered a denser medium, where it travels slower.

Hint 3

When the first and last media are the same, think of a glass slab: how do the incident and emergent rays compare?

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)(i) At the A–B surface the ray bends towards the normal (). So medium B is optically denser than A, and light slows down in B. Hence speed of light in A > speed of light in B.

    ½ mark

  2. (a)(ii) Inside the ray diagram the ray continues from B into C without changing its direction. So B and C have the same optical density.

    ½ mark

  3. (b) Ray diagram (glass-slab type: A = C, B denser). Draw a rectangular block B with medium A above it and medium C below it. Draw a normal at the top surface. Draw an incident ray in A, with an arrow, striking the top surface at angle .

    ½ mark

  4. Inside B, draw the refracted ray bending towards the normal, with angle . This happens because B is denser than A.

    ½ mark

  5. At the lower surface draw a second normal. Draw the emergent ray in C bending away from the normal, with an arrow. Since C has the same optical density as A, the angle of emergence equals .

    ½ mark

  6. Show the emergent ray parallel to the incident ray but shifted sideways (lateral displacement). Mark the direction of the rays with arrows throughout.

    ½ mark

Answer: (a)(i) Speed in A > speed in B; (ii) B and C have equal optical density. (b) Ray bends towards the normal entering B and away from it entering C; the emergent ray is parallel to the incident ray and laterally displaced.

Where the marks are

  • Speed of light in A greater than in B (½ mark)
  • B and C have the same optical density (½ mark)
  • Correct ray diagram: bending towards the normal in B, away from it in C, emergent ray parallel to incident ray, arrows shown (2 marks; ½ deducted if ray directions are not shown)

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 paper2026 board paper, set 31/4/1: 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.