Assertion (A) : Sound travels faster in humid air than in dry air.

Reason (R) : The increase of moisture in air tends to decrease the density of air.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : Two persons on the surface of moon can not talk to each other.

Reason (R) : The speed of sound decreases with the decrease in temperature.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : The speed of ultrasound waves is higher than supersonic waves.

Reason (R) : Supersonic is used for objects travelling with speed greater than speed of sound in air.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Three observers hear the sound of an explosion from the same distance but through different media.

Observer A hears the sound through air, B hears it through water, and C hears it through steel.

(a) Arrange the observers in the order in which they would hear the sound first.

(b) In which medium will the sound travel the fastest and why?

(c) On a cold morning, sound from a distant train is heard more clearly than during noon. Give reason.

(d) "Solids are heavier, therefore sound should travel slower in them." Analyse this statement.

(e) If sound could travel in vacuum, what property of sound would have to change?