Skip to content

A plano-convex lens of focal… (Class 12 Physics 2024, Q18b)

questionbuddy.in/q/cbse-12-physics-2024-55-1-1-q18b-plano-convex-lens-focal-length

PhysicsCBSE Class 12 · Board exam 2024, set 55/1/1 · 2 marks · Very short answer

CBSE Class 12 Physics 2024: question 18(b)

Set in the CBSE Class 12 board exam of 2024, paper 55/1/1, section B, question 18(b), for 2 marks. Try it first; the hints and our step-by-step solution are below.

Q18(b) · 2 marks · Very short answerRay Optics and Optical Instruments

A plano-convex lens of focal length 16 cm is made of a material of refractive index 1.4. Calculate the radius of the curved surface of the lens.

Source: official question paper from cbse.gov.in (PDF). See it in the full 2024 board paper, set 55/1/1.

Hints

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

Hint 1

Use the lens maker's formula.

Hint 2

For a plane surface the radius of curvature is infinite, so its term is zero.

Hint 3

Solve .

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. Lens maker's formula: . For a plano-convex lens, and , so .

    1 mark

  2. Substituting: , so cm.

    1 mark

Answer: R = 6.4 cm

Where the marks are

  • Applies the lens maker's formula with for the plane face (1 mark)
  • Obtains R = 6.4 cm (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 paper2024 board paper, set 55/1/1: 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.