Which one of the following statements about sound is NOT correct ?
Sound travels at a speed slower than the speed of light
Sound waves are transverse waves
Sound waves are longitudinal waves
Sound travels faster in moist air than in dry air
Answer is Right!
Answer is Wrong!
This question was previously asked in
UPSC NDA-2 – 2020
A) Sound travels at a speed slower than the speed of light: This is correct. The speed of light in vacuum is approximately 3 x 10⁸ m/s, while the speed of sound in air is approximately 343 m/s at room temperature.
B) Sound waves are transverse waves: This is NOT correct. Sound waves in a gas or liquid are longitudinal waves, meaning the particle displacement is parallel to the direction of wave propagation (compressions and rarefactions). Sound waves in solids can have both longitudinal and transverse components.
C) Sound waves are longitudinal waves: This is correct for sound in air or liquids.
D) Sound travels faster in moist air than in dry air: This is generally correct. At the same temperature and pressure, moist air is slightly less dense than dry air because water molecules (molecular mass ~18) replace nitrogen (N₂, ~28) and oxygen (O₂, ~32) molecules. While density decreases, the bulk modulus also changes. The effect of lower density dominates, leading to a slightly higher speed of sound in moist air.
The statement that is NOT correct is B.