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A tank is filled with a… (Class 12 Physics 2026, Q19)

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PhysicsCBSE Class 12 · Board exam 2026, set 55/5/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2026: question 19

Set in the CBSE Class 12 board exam of 2026, paper 55/5/1, section B, question 19, for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q19 · 2 marks · Very short answerRay Optics and Optical Instruments

A tank is filled with a liquid to a height of 12·5 m. The apparent depth of a needle lying at the bottom of the tank is measured to be 9·0 m. Calculate the speed of light in the liquid.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2026 board paper, set 55/5/1.

Hints

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

Hint 1

Apparent depth is less than real depth because of refraction.

Hint 2

n = real depth / apparent depth; then use n = c/v.

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. Refractive index of the liquid:

    1 mark

  2. 1 mark

Answer: v ≈ 2.16 × 10^8 m/s

Where the marks are

  • Finds n = real depth/apparent depth ≈ 1.39 (1 mark)
  • Uses v = c/n to get m/s (1 mark)

Revise the chapter

Practise this chapterBoard-style questions from Ray Optics and Optical Instruments, one at a time, marked against the answer key and marking points.Back to the full paper2026 board paper, set 55/5/1: 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.