Absolute refractive index of glass and water is 3/2 and 4/3 respectively. If the speed of light in glass is 2 × 10^8 m/s, the speed of light in water is : (A) 9/4 × 10^8 m/s (B) 5/2 × 10^8 m/s (C) 7/3 × 10^8 m/s (D) 16/9 × 10^8 m/s

ScienceCBSE Class 10 · Board exam 2024, set 31/4/1 · 1 mark · MCQ

CBSE Class 10 Science 2024: question 11

Set in the CBSE Class 10 board exam of 2024, paper 31/4/1, section A, question 11, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q11 · 1 mark · MCQLight – Reflection and Refraction

Absolute refractive index of glass and water is $\frac{3}{2}$ and $\frac{4}{3}$ respectively. If the speed of light in glass is $2 \times 1 0^{8}$ m/s, the speed of light in water is :

(A) $\frac{9}{4} \times 1 0^{8}$ m/s
(B) $\frac{5}{2} \times 1 0^{8}$ m/s
(C) $\frac{7}{3} \times 1 0^{8}$ m/s
(D) $\frac{16}{9} \times 1 0^{8}$ m/s

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 31/4/1.

Hints

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

Hint 1

Write the formula for absolute refractive index.

Hint 2

$n_{1} v_{1} = n_{2} v_{2}$ .

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.

Since $n = c / v$ , the product $n v = c$ is the same for both media: $n_{g} v_{g} = n_{w} v_{w}$ .
$\frac{3}{2} \times 2 \times 1 0^{8} = \frac{4}{3} v_{w}$ , so $v_{w} = \frac{9}{4} \times 1 0^{8}$ m/s.
1 mark

Answer: (A) 9/4 × 10^8 m/s

Where the marks are

Uses $n v$ = constant to get $\frac{9}{4} \times 1 0^{8}$ m/s (1 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 paper2024 board paper, set 31/4/1: every question, by section.

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CBSE Class 10 Science 2024: question 11

Hints

Step-by-step solution

Revise the chapter

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