PhysicsCBSE Class 12 · Sample paper, session 2024-25 · 1 mark · MCQ

CBSE Class 12 Physics sample paper 2024-25: question 9

From the official CBSE sample question paper for 2024-25, section A, question 9, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q9 · 1 mark · MCQRay Optics and Optical Instruments

A point object is placed at the centre of a glass sphere of radius 6 cm and refractive index 1.5. The distance of virtual image from the surface of the sphere is

(A)2 cm
(B)4 cm
(C)6 cm
(D)12 cm

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2024-25.

Hints

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

Hint 1

Use refraction at a single spherical surface.

Hint 2

Rays from the centre travel along radii and are not deviated.

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.

Apply $\frac{n _{2}}{v} - \frac{n _{1}}{u} = \frac{n _{2} - n _{1}}{R}$ with $n_{1} = 1.5$ , $n_{2} = 1$ , $u = - 6$ cm and $R = - 6$ cm: $\frac{1}{v} + \frac{1.5}{6} = \frac{- 0.5}{- 6}$ .
½ mark
This gives $\frac{1}{v} = \frac{1}{12} - \frac{3}{12} = - \frac{1}{6}$ , so $v = - 6$ cm. The image is at the centre, 6 cm from the surface. The answer is (C).
½ mark

Answer: 6 cm, option (C)

Where the marks are

Correct refraction formula with sign convention (0.5 mark)
$v = - 6$ cm (0.5 mark)

Revise the chapter

Chapter: Ray Optics and Optical Instruments (notes, formulas, where marks are lost and every past question)
Topic: Refraction at Spherical Surfaces and Lenses

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 paperSample paper 2024-25: every question, by section.

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CBSE Class 12 Physics sample paper 2024-25: question 9

Hints

Step-by-step solution

Revise the chapter

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