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A glass prism has… (Class 12 Physics SQP 2025-26, Q5)

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PhysicsCBSE Class 12 · Sample paper, session 2025-26 · 1 mark · MCQ

CBSE Class 12 Physics sample paper 2025-26: question 5

From the official CBSE sample question paper for 2025-26, section A, question 5, for 1 mark. Try it first; the hints and our step-by-step solution are below.

Q5 · 1 mark · MCQRay Optics and Optical Instruments

A glass prism has internal angles of , and . The glass has a critical angle of . Which of the following ray diagrams depicts the possible path the of light through the prism?

  1. (A)Ray diagram (A): prism ABC with right angle at A on the left; ray enters vertically at the top near B, and a ray emerges downward near C.
  2. (B)Ray diagram (B): prism with right angle at A at top, hypotenuse CB at the bottom; ray enters downward on one side and emerges upward on the other side after two total internal reflections.
  3. (C)Ray diagram (C): prism with right angle at A on the left, B top, C bottom; ray enters horizontally on the face and returns back reversed.
  4. (D)Ray diagram (D): prism with right angle at A at bottom, B and C at top; ray enters horizontally and emerges obliquely out of the face near C.

Figure in the paper: Four ray diagrams (A)-(D) through a right-angled isosceles prism ABC with right angle at A. See it in the official paper.

Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2025-26.

Hints

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

Hint 1

Find the angle at which a normally entering ray strikes the hypotenuse.

Hint 2

Compare that angle with the critical angle.

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. A ray entering normally through a short face meets the hypotenuse at an angle of incidence of , which equals the critical angle.

  2. At or beyond the critical angle the light is totally internally reflected, turned through , and leaves normally through the other face. This path is shown in diagram (A).

    1 mark

Answer: Option (A): total internal reflection

Where the marks are

  • Recognises incidence of 45° on the hypotenuse, giving total internal reflection, and chooses (A) (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 paperSample paper 2025-26: 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.