UPSC Prelims 2013 Q72: Geography – Atmosphere & Climatology
During a thunderstorm, the thunder in the skies is produced by the
1. Meeting of cumulonimbus clouds in the sky
2. Lightning that separates the nimbus clouds
3. Violent upward movement of air and water particles
Select the correct answer using the codes given below.
- (a) 1 only
- (b) 2 and 3
- (c) 1 and 3
- (d) None of the above produces the thunder
Answer: (d) None of the above produces the thunder
Explanation
What produces thunder?
Thunder is the sound made by lightning.
A lightning flash heats the air in its path to about 30,000 degrees Celsius in a split second.
The air expands explosively and then contracts, sending out a shock wave that we hear as thunder.
| Statement | Verdict | Reason |
|---|---|---|
| 1. Meeting of cumulonimbus clouds in the sky | Incorrect | Clouds do not 'collide' to make sound |
| 2. Lightning that separates the nimbus clouds | Incorrect | Lightning does not separate clouds |
| 3. Violent upward movement of air and water particles | Incorrect | This builds up electric charge, but it is not the source of the sound |
Thunderstorm facts:
| Feature | Detail |
|---|---|
| Cloud | Cumulonimbus |
| Why we see the flash first | Light travels far faster than sound |
| Distance | About one kilometre for every three seconds between flash and thunder |
Answer: (d) None of the above produces the thunder.
Why each option is right or wrong
- (a) Incorrect. The meeting of clouds does not produce thunder.
- (b) Incorrect. Lightning does not separate clouds; nor is that the cause.
- (c) Incorrect. Neither cloud contact nor the upward movement of air makes the sound.
- (d) CORRECT. Thunder comes from the sudden heating and expansion of air by lightning.
Key point
Thunder: lightning heats air to about 30,000 degrees Celsius; the explosive expansion makes a shock wave. Light arrives before sound.
Remember
Thunder = air heated and expanded by lightning.
Common mistakes
- Believing the old idea that clouds colliding cause thunder.
- Confusing what causes lightning (charge separation) with what causes thunder.
- Avoiding the 'None of the above' option.
Exam tip
Lightning is the cause; thunder is the sound of air expanding.
Sources
- NCERT Class VIII — Science, Ch 15 (Some Natural Phenomena)
- India Meteorological Department — Frequently Asked Questions on Thunderstorms and Lightning