Sound

​Sound

By Mr Math n Physics

​Describing Sound

​ Sound waves are produced by vibrating sources

​Sound waves are Longitudinal, So a medium is needed to transmit sound waves. This means if there are no molecules, such as in a vacuum, then the sound can’t travel through it

​Longitudinal waves are usually drawn as several lines to show that the wave is moving parallel to the direction of energy transfer. Drawing the lines closer together represents the compressions. Drawing the lines further apart represents the rarefactions.

​ Representing longitudinal waves

​Compression & rarefaction

​Longitudinal waves consist of compressions and rarefactions:
A compression is a region of higher density i.e. a place where the molecules are bunched together
A rarefaction is a region of lower density i.e. a place where the molecules are spread out

​Measuring the Speed of Sound

​ Experiment 2: measuring the speed of sound with oscilloscopes

Multiple Choice

In which situation do sound waves not travel?

• from a satellite in space to Earth

• from a ship to a submarine

• from an explosion underground to the surface

• through a balloon filled with helium gas

Multiple Choice

Which of the following does not produce a sound wave?

• a bell ringing under water

• a gun fired in a room with no echoes

• a hammer hitting a block of rubber

• an explosion in outer space

Multiple Choice

Sound travels at different speeds in air, water and steel. For these materials, which row is correct?

• A

• B

• C

• D

Multiple Choice

In an experiment to determine the speed of sound in air, a student stands 200 m away from a cliff and claps two pieces of wood together. His class-mates standing next to him start stopwatches when the two pieces of wood meet and stop the stopwatches when they hear the echo. Their times are:

1.44 s 1.70 s 1.58 s

Which value for the speed of sound do they obtain?

• 62 m/s

• 123 m/s

• 247 m/s

• 340 m/s

Multiple Choice

A student stands at a distance d from the base of a tall cliff. He claps together two pieces of wood and measures the time that elapses before he hears the echo. He conducts the experiment five times and obtains these results.

0.72 s 0.8 s 0.7 s 0.8 s 0.7s

The speed of sound is 320 m/s. What is the distance d?

• 120 m

• 240 m

• 480 m

• 600 m

Multiple Choice

During a thunderstorm, there is an interval of 1.70 s between an observer seeing the lightning and hearing the thunder. The speed of sound is 340 m/s. What is the distance between the observer and the storm?

• 100 m

• 200 m

• 578 m

• 1160 m

Multiple Choice

A boy strikes a rigid metal fence with a stick to create a sound along the fence. A girl listens with her ear against the fence. One second after the fence is struck, the girl hears a sound through the air. How long will it take for the sound to reach the girl through the fence?

• 0 second

• less than 1 second

• 1 second

• more than 1 second

​Pitch & loudness

​Ultrasound

​The approximate range of frequencies audible to humans is 20 Hz to 20 000 Hz in frequency. Ultrasound is defined as sound with a frequency higher than 20 kHz

​Uses of ultrasound

​Ultrasound is used in:
1. non-destructive testing of materials
2. medical scanning of soft tissue
3. sonar to calculate the depth or
distance from time and wave speed

Multiple Choice

Two sound waves X and Y are compared. X has the greater frequency. Y has the greater amplitude. How do the loudness and pitch of sound wave Y compare to those of X?

• Y is louder and higher pitch.

• Y is louder and lower pitch.

• Y is quieter and higher pitch.

• Y is quieter and lower pitch.

Multiple Choice

A musical note is produced by two sources. The traces produced by each source on the screen of a cathode-ray oscilloscope (c.r.o.) are shown below. What is the difference between the sounds?

• the amplitude

• the frequency

• the speed

• the quality

Multiple Choice

A loudspeaker produces a sound wave of frequency 50 Hz. The amplitude of the sound wave is increased. What is heard?

• a louder sound of a higher pitch

• a louder sound of the same pitch

• a sound of higher pitch but the same loudness

• a sound of the same pitch and loudness as before

Multiple Choice

A guitar string is made to vibrate. What makes the pitch of the note rise?

• a decrease in the amplitude of vibration

• a decrease in the frequency of vibration

• an increase in the amplitude of vibration

• an increase in the frequency of vibration

Multiple Choice

Which frequency is in the ultrasound range?

• 35 Hz

• 350 Hz

• 3500 Hz

• 35000 Hz

Multiple Choice

Which range is the approximate range of audible frequencies for a human?

• A

• B

• C

• D

Multiple Choice

The diagrams show oscilloscope traces of sounds picked up by microphones. The oscilloscope controls are set in the same position for all the traces. Which trace shows the sound that is both loud and low-pitched?

Multiple Choice

The diagram shows the trace produced on a cathode-ray oscilloscope (c.r.o.) by a sound. Which trace is produced when both the loudness and the pitch of the sound are increased?

Multiple Choice

Ultrasound has many uses. For what are ultrasound waves used?

• killing cancerous cells

• pre-natal scanning

• sunbeds

• telephones

Multiple Choice

An ultrasound scanner produces an image of an unborn baby. How does the scanner form an image?

• from ultrasound absorbed by the baby

• from ultrasound emitted by the baby

• from ultrasound refracted by the baby

• from ultrasound reflected by the baby

Multiple Choice

An ultrasonic tape-measure is used to find the distance to a wall. It sends out an ultrasonic pulse and times how long it takes for the reflected pulse to return from the wall. The ultrasound has a frequency, a wavelength and a speed. Which pair of values is needed to find the distance to the wall?

• frequency and wavelength

• frequency and time taken for the pulse to return

• speed and time taken for the pulse to return

• wavelength and time taken for the pulse to return

Multiple Choice

The sound from the siren of a ship is reflected by a cliff. An echo is heard by a sailor on the deck of the ship, 4.0 s after the siren is sounded. The speed of sound in air is 320 m/s. How far from the cliff is the ship?

• 80 m

• 160 m

• 640 m

• 1280 m

Multiple Choice

A girl, standing 150 m in front of a tall building, fires a shot using a starting pistol. A boy, standing 350 m from the girl, hears two bangs 1 s apart. From this information, what is the speed of sound in air?

• 300 m/s

• 350 m/s

• 500 m/s

• 650 m/s