# Problems: Properties of Sound

#### Question 1

Fig. below shows the cone of a loudspeaker that is producing sound waves in air.

At any given moment, a series of compressions and rarefactions exist along the line XY.

(a) Copy the figure and use the letter C to mark three compressions and the letter R to mark three rarefactions along XY.

(b) Explain what is meant by

(i) a compression,

(ii) a rarefaction.

(c) A sound wave is a longitudinal wave. With reference to the sound wave travelling along XY in Fig. explain what is meant by a longitudinal wave.

(d) There is a large vertical wall 50 m in front of the loudspeaker. The wall reflects the sound waves.

The speed of sound in air is 340 m/s.

Calculate the time taken for the sound waves to travel from X to the wall and to return to X.

#### Question 2

Fig. shows how the air pressure at one instant varies with distance along the path of a continuous sound wave.

(a) What type of waves are sound waves?

(b) On Fig, mark on the axis PY

(i) one point C where there is a compression in the wave,

(ii) one point R where there is a rarefaction in the wave.

(c) Describe the motion of a group of air particles situated on the path of the wave shown in

(d) The sound wave shown has the speed of 340 m/s and a frequency of 200 Hz.

Calculate the distance represented by PX on Figure.

#### Question 3

Fill in the missing words:

1. Sound is caused by . . . . . . . . . . . . . . . . . . . . .
2. A sound wave consists of places at higher pressure (called . . . . . . . . . . . . . . .) and places of . . . . . . . . . . . . . . pressure (called . . . . . . . . . . . . . . .. . . . . .. . .)
3. Wave speed (in metres per second) equals frequency (in . . . . . . . . . ) multiplied by . . . . . . . . . . . . . . . . . . (in  . . . . . . . . . .)
4. Sound cannot travel through a . . . . . . . . . . . . . . . . . . .
5. Echoes are caused by the . . . . . . . . . . . . . . . . . . . . . of sound.
6. The speed of sound in a solid is . . . . . . . . . . . . . . . . . . than the speed of sound in air.
7. Ultrasounds have a . . . . . . . . . . . . . . . . . . above . . . . . . . . . . Hz and so have a short . . . . . . . . . . . . . . . . . . .
They have many uses, including pre-natal . . . . . . . . . . .
8. Pitch depends on . . . . . . . . . . . . . . . . . .
Loudness depends on . . . . . . . . . . . . . . . . . .
Quality depends on . . . . . . . . . . . . . . . . . .