CBSE Class 12 Physics sample paper 2026-27: question 6
From the official CBSE sample question paper for 2026-27, section A, question 6, for 1 mark. Try it first; the hints and our step-by-step solution are below.
Q6 · 1 mark · MCQWave Optics
If wave front from star in nearby galaxy is detected by a telescope at the top of some mountain in India then the shape of the wavefront detected will be
- (A)diverging spherical
- (B)converging spherical
- (C)plane
- (D)cylindrical
Source: official sample paper from cbseacademic.nic.in (PDF). See it in the full Sample paper 2026-27.
Hints
Open one hint at a time and try again before the next.
Hint 1
How far away is the source?
Hint 2
What does a small part of a very large sphere look like?
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.
- ½ mark
A star is a point source at an enormous distance from the Earth.
- ½ mark
A spherical wavefront of very large radius is practically plane, so the telescope detects a plane wavefront. Option (C).
Answer: Plane, option (C)
Where the marks are
- Treats the distant star as a point source at infinity, giving a plane wavefront (1 mark)
Revise the chapter
- Chapter: Wave Optics (notes, formulas, where marks are lost and every past question)
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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.