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Topic Speed of light
Asked 6 times across 3 UPSC exams over 38 years (1985–2023), peaking in 2021.
Key insights
- Most tested in CSE — 3 of 6 PYQs
- Most asked in 2021
- Recurs across 5 years (1985–2023)
How it travelled across exams
First appearance in each exam — the same idea, reframed.
CSE 1985 → CDS 2020 → NDA 2021
How the concept evolved
Rising — more than half its appearances (4 of 6) 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.
NDA2023
The flash of lightning is seen before the thunderstorm is heard. It verifies that
- A sound travels much faster than light
- B light travels much faster than sound ✓
- C light and sound both travel with same speed
- D intensity of flash of lightning is very high during thunderstorm
✓ Correct answer: (B)
Science & Technology › Physics & Chemistry
CSE2021
Which one of the following is a reason why astronomical distances are measured in light-years?
- A Distances among stellar bodies do not change.
- B Gravity of stellar bodies does not change.
- C Light always travels in straight line.
- D Speed of light is always same. ✓
✓ Correct answer: (D)
Science & Technology › Space Tech
NDA2021
Which one of the following statements is not correct for light rays ?
- A Light travels at different speeds in different media.
- B Light travels at almost 300 million metres per second in air.
- C Light speeds down as it leaves a water surface and enters the air. ✓
- D Light speeds up as it leaves a glass surface and enters air.
✓ Correct answer: (C)
Science & Technology › Physics & Chemistry
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