UPSC Prelims 2006 Q4: Science & Technology – Physics
In which one among the following is the speed of sound maximum?
- (a) Air at 0 °C
- (b) Air at 100 °C
- (c) Water
- (d) Wood
Answer: (d) Wood
Explanation
Speed of sound in different media
Sound is a mechanical wave, so it travels fastest where the medium is stiffest relative to its density. The general order is solids > liquids > gases.
| Medium | Approx. speed of sound |
|---|---|
| Air at 0 °C | about 331 m/s |
| Air at 100 °C | about 386 m/s (rises with temperature) |
| Water | about 1,480 m/s |
| Wood (a solid) | about 3,000-4,000 m/s |
Wood is a solid with strong inter-particle forces, so the speed of sound is maximum in wood.
Answer: (d) Wood.
Why each option is right or wrong
- (a) Incorrect. Air at 0 °C has the lowest speed here, about 331 m/s.
- (b) Incorrect. Air at 100 °C is faster than cold air, about 386 m/s, but still far below liquids and solids.
- (c) Incorrect. Water carries sound at about 1,480 m/s, faster than air but slower than a solid like wood.
- (d) CORRECT. Wood, being a solid, transmits sound fastest of the four, at several thousand metres per second.
Key point
Speed of sound follows the order solids > liquids > gases, so among air, water and wood, the speed is maximum in wood.
Remember
Sound is fastest in solids, slower in liquids, slowest in gases.
Common mistakes
- Assuming a denser medium always carries sound slower; elasticity matters more than density alone.
- Thinking hot air can beat water; temperature raises speed in air only modestly.
- Confusing the speed of sound with the speed of light, which behaves the opposite way.
Exam tip
For 'maximum speed of sound' questions, pick the solid; for 'minimum', pick the gas at the lowest temperature.
Sources
- NCERT Class VIII Science — Sound
- NCERT Class IX Science — Sound