ScienceCBSE Class 10 · Sample paper, session 2023-24 · 2 marks · Very short answer

CBSE Class 10 Science sample paper 2023-24: question 24

From the official CBSE sample question paper for 2023-24, section B, question 24, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q24 · 2 marks · Very short answerCompetency-basedLight – Reflection and Refraction

The refractive indices of three media are given below:

Medium	Refractive Index
A	1.6
B	1.8
C	1.5

A ray of light is travelling from A to B and another ray is travelling from B to C.

(a) In which of the two cases the refracted ray bends towards the normal?
(b) In which case does the speed of light increase in the second medium?
Give reasons for your answer.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2023-24.

Hints

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

Hint 1

Compare the refractive indices of the first and second medium in each case.

Hint 2

Higher refractive index means optically denser. Use $v = c / n$ to compare speeds.

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.

(a) A ray bends towards the normal when it goes from an optically rarer medium (lower refractive index) into an optically denser medium (higher refractive index).
½ mark
For A → B: $n_{A} = 1.6$ and $n_{B} = 1.8$ , so $n_{B} > n_{A}$ . B is denser than A. The ray going from A to B bends towards the normal. (For B → C, $n_{C} < n_{B}$ , so that ray bends away from the normal.)
½ mark
(b) Speed of light in a medium: $v = \frac{c}{n}$ . So the smaller the refractive index, the greater the speed of light.
½ mark
For B → C: $n_{C} = 1.5 < n_{B} = 1.8$ , so $v_{C} > v_{B}$ . The speed of light increases when the ray goes from B to C.
½ mark

Answer: (a) Ray from A to B bends towards the normal, since $n_{B} > n_{A}$ . (b) Speed increases for the ray from B to C, since $n_{C} < n_{B}$ and $v = c / n$ .

Where the marks are

States that a ray going from rarer to denser medium bends towards the normal (0.5 mark)
Identifies A → B as the case, using $n_{B} > n_{A}$ (0.5 mark)
Uses $v = c / n$ , so speed is larger where n is smaller (0.5 mark)
Identifies B → C as the case where speed increases, using $n_{C} < n_{B}$ (0.5 mark)

Revise the chapter

Chapter: Light – Reflection and Refraction (notes, formulas, where marks are lost and every past question)
Topic: Refraction of Light and Refractive Index

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 2023-24: every question, by section.

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CBSE Class 10 Science sample paper 2023-24: question 24

Hints

Step-by-step solution

Revise the chapter

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