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Topic Refractive index
Asked 10 times across 4 UPSC exams over 32 years (1994–2026), peaking in 1994.
Key insights
- Most tested in NDA — 4 of 10 PYQs
- Most asked in 1994
- Recurs across 5 years (1994–2026)
How it travelled across exams
First appearance in each exam — the same idea, reframed.
CSE 1994 → NDA 2020 → CDS 2020 → GEO 2022
How the concept evolved
Rising — more than half its appearances (8 of 10) are since 2016.
Related concepts
Ideas UPSC tests alongside this one — keep exploring.
Sample questions
You've seen the pattern — here are a few of the actual PYQs.
NDA2026
A periscope uses two plane mirrors inclined at 45°. If the tube of the periscope is filled with a complete transparent liquid of refractive index 1·5, then which one of the following is correct in respect of the image seen?
- A The image will remain unchanged. ✓
- B The image will appear laterally shifted.
- C The image will appear 1·5 times brighter.
- D The image will appear 1·5 times darker.
✓ Correct answer: (A)
Science & Technology › Physics & Chemistry
NDA2026
A glass slab of refractive index 1·5 is cut in the shape of a parallelepiped ABCD as shown in the figure. Surface BC is polished to form a perfect reflector. Light is incident at surface AB from inside at an angle π/3. Which one of the following is the correct angle ABC (θ) such that the reflected light retraces its path?
- A π/6
- B π/3 ✓
- C π/4
- D 5π/12
✓ Correct answer: (B)
Science & Technology › Physics & Chemistry
GEO2025
An electromagnetic wave with its magnetic field B = 0.3cos(8y - 10^8 t) ĵ tesla is propagating in a non-magnetic dielectric medium of refractive index 2. The wavelength of the wave is
- A 6π m
- B 3π m ✓
- C 0.3 m
- D (2π/3) m
✓ Correct answer: (B)
Science & Technology › Physics & Chemistry
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