AQA GCSE 3-2B

Sound

GCSE Physics pages 244 to 251

April 10th 2010

AQA GCSE Specification

SOUND13.5 What is sound?

Using skills, knowledge and understanding of how science works:• to compare the amplitudes and frequencies of sounds from diagrams of oscilloscope traces.

Skills, knowledge and understanding of how science works set in the context of:• Sound is caused by mechanical vibrations and travels as a wave.• Sounds in the range 20-20 000 Hz can be detected by the human ear.• Sound cannot travel through a vacuum.• The pitch of a note increases as the frequency increases.• The loudness of a note increases as the amplitude of the wave increases.• The quality of a note depends upon the waveform.• Sound waves can be reflected and refracted.

ULTRASOUND13.6 What is ultrasound and how can it be used?

Using skills, knowledge and understanding of how science works:

• to compare the amplitudes and frequencies of ultrasounds from diagrams of oscilloscope traces

• to determine the distance between interfaces in

Skills, knowledge and understanding of how science works set in the context of:

• Electronic systems can be used to produce ultrasound waves which have a frequency higher than the upper limit of hearing for humans.

• Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflections to reach a detector is a measure of how far away such a boundary is.

• Ultrasound waves can be used in industry for cleaning and quality control.

• Ultrasound waves can be used in medicine for pre-natal scanning.

SoundSound is produced by vibrating objects.

A sound wave consists of mechanical vibrations in air and other substances.

Sound is a longitudinal wave in which the wave energy travels in the same direction as the particles within the wave vibrate.

Most other types of wave are transverse. For examaple water and light waves. In these cases the particles making up the wave vibrate at ninety degrees to the direction of energy transfer.

wave direction

vibrations

LONGITUDINAL WAVE

wave direction

vibrations

TRANSVERSE WAVE

Through air a sound wave consists of a series of compressions and rarefactions.A compression is a region of slightly higher pressure where the air molecules are closer together than usual. A rarefaction is the opposite.

no sound wavesound wave

wavelength

loudspeaker

rarefaction

compression

Speed of soundSubstance Speed in m/s

Air at 0ºC 330

Air at 20ºC 342

Water at 20ºC 1 500

Steel at 20ºC 5 000

Sound does not travel through a vacuum.In space no one can hear you scream!

– tagline of the film Alien (1979)

330

342

1 500

5 000

QuestionA thunderclap is heard 12 seconds after a lightning flash. Calculate the distance to the lightning flash.Take the speed of sound = 340 m/s

speed = distance / timebecomes: distance = speed x time= 340 m/s x 12 seconds= 4 080 m

Distance = 4.08 km

Bell jar experimentThis experiment shows that sound needs a material medium for transmission.

As the air pressure inside the bell jar is reduced the loudness of the sound heard outside decreases.

The bell can be still seen to be working normally.

Range of hearingHumans can hear sounds in the range 20 Hz to 20 000 Hz.

Age and damage reduces the upper limit. For example an old person or someone exposed to perlonged high sound volume may no be able to hear above 10 000 Hz.

Some animals can hear much higher frequencies:dogs – 40 000 to 60 000 Hz (depends on the breed)bats and dolphins – 100 000 Hz

Reflection of sound

Question:A missguided child shouts ‘Chelsea!’ at a nearby cliff and hears their echo 1.4 s later. How far away is the cliff?Take the speed of sound = 340 m/s. distance, D

The sound travels to and from the cliff, a total distance of 2Dspeed = distance / time becomes: distance = speed x time= 340 m/s x 1.4 s= 476 m= 2D !Therefore distance to the cliff = 238 m.

An echo is a reflected sound wave.

cooler air

A BC

The sound produced by person A may be heard more clearly by person B than by person C.

The cooler air over the water refracts the sound waves downwards.

Sound refraction

Sound Notes questions from pages 244 & 245

1. (a) What type of objects produce sound waves? (b) What is the typical range of frequencies audible to a young person? (c) How does this range change with age?

2. Draw a diagram and describe an experiment to show that sound waves do not travel through a vacuum.

3. Draw Figure 1 on page 244 and explain the difference between longitudinal and transverse waves. State which type is sound.

4. (a) What is an echo? (b) How are echoes affected by the surface of materials?

5. Why does sound travel better at night?6. Copy and answer questions (a), (b), (c), (d) and (e) on pages 244

and 245.7. Copy the ‘Key points’ table on page 245.8. Answer the summary questions on page 245.

Sound ANSWERS

In text questions:(a) A mouse.(b) The sound becoming

audible again. (c) Wave one end from side to

side.(d) There are no reflections, so

each note dies away more quickly outdoors.

(e) Colder.

Summary questions:1. (a) Reflected.

(b) Scattered, absorbed. (c) Refracted.

2. (a) About 18000 Hz (b) The vibrating surface of the

loudspeaker pushes the air near it to and fro, creating sound waves which spread out from the loudspeaker.

(c) The ball inside goes around at constant speed and makes the surrounding air vibrate.

Sound waves on oscilloscopesAn oscilloscope is a device that can be used to display a sound wave.

The screen displays a graph of how the amplitude of the sound wave varies with time.

LoudnessThe loudness of a sound increases with the amplitude of the sound wave.

quiet

loud

PitchThe pitch of a musical note increases with frequency.

Examples:Concert pitch A = 440 Hz; Top C = 523 Hz

Doubling the frequency increases the pitch by one octave. Therefore the ‘A’ above top C will have frequency 880 Hz.

low pitch high pitch

QualityThe quality or timbre of a musical note is what makes one musical instrument sound different from another.

Despite different instruments producing a note of the same loudness and pitch, the shape of the wave will be different.

QuestionThe diagram opposite shows the appearance of a sound wave on an oscilloscope. Draw a second diagram showing the appearance of a sound wave of lower pitch but greater loudness.

QuestionChoose appropriate words to fill in the gaps below:

Sound is a ___________ wave that in air consists of a series of compressions and _____________.

Sound travels fastest through _______ but does not travel at all through a __________.

A ____________ sound wave is called an echo. Sound also undergoes ___________.

The loudness of a sound increases with wave __________, the pitch with wave ____________.

reflected

refractionrarefactions

longitudinal

solidsvacuum

WORD SELECTION:

amplitude

frequency

reflected

refraction

rarefactions

longitudinal

solids

vacuum

amplitude

frequency

Musical sounds Notes questions from pages 246 & 247

1. Explain the difference between a musical note and noise.2. Draw wave diagrams to explain what happens when there is

an increase in a sound wave’s (a) loudness and (b) pitch.3. Copy and answer questions (a), (b) and (c) on pages 246

and 247.4. Explain how the three main categories of musical instrument

produce sound.5. Why do different musical instruments producing the same

note sound different from each other? Illustrate your answer with a waveform diagram.

6. Copy the ‘Key points’ table on page 247.7. Answer the summary questions on page 247.

Musical sounds ANSWERS

In text questions:(a) An ambulance, a police vehicle,

a fire engine, an ice cream van.(b) The waves are not as tall.(c) The waves would be smaller in

height and stretched out more.

Summary questions:1. (a) The waves would be taller but

would have the same spacing.(b) The waves would be more stretched out but would have the same height.

2. (a) (i) The note has a higher pitch (frequency).(ii) The note has a higher pitch (frequency).

(b) The sound of a violin (played correctly) lasts as long as the violin bow is in contact with a string. The sound of a drum dies away after the drum skin has been struck. A drum note is less rhythmical than a violin note.

UltrasoundUltrasound is very high frequency sound that is above 20 000 Hz, too high to be heard by humans.

Some animals, for example dogs, bats and dolphins can communicate or navigate using ultrasound.

Ultrasound echoes can be used to measure distance (e.g. sonar) and to see inside objects (scans).

Sonar

SOund Navigation And Ranging.

Ultrasound scans

Ultrasound waves are partially reflected when they meet a boundary between two different media. The time taken for the reflections to reach a detector is a measure of how far away such a boundary is.

Developing baby

Ultrasound transmitter

Ultrasound reflects off each tissue boundary

1. Prenatal scanning

2. Quality control

Ultrasonic testing is a type of nondestructive testing commonly used to find flaws in materials and to measure the thickness of objects.

At a construction site, a technician tests a pipeline weld for defects using an ultrasonic instrument.

QuestionThe oscilloscope trace opposite was obtained from the scan of a metal block.(a) how many flaws are present according to this display?(b) If the width of the block was 300 mm calculate the distance fro the front of the block to each flaw.

(a) There are two flaws.

(b) The width of the block is represented by 8.3 squares.Therefore each square represents 300mm / 8.3= 36.1 mm per square

The two flaws occur after 3.0 and 4.2 squaresTherefore:1st flaw is at 3.0 x 36.1= 108 mm from the front2nd flaw is at 4.2 x 36.1= 152 mm from the front

Ultrasound cleaningThe very high frequency waves of ultrasound can be used to shake off dirt or grease.

Jewellery immersed in water

Another way of cleaning teeth

QuestionChoose appropriate words to fill in the gaps below:

Ultrasound is very high ___________ sound. It is above the upper range of _________ hearing, more than 20 000 _______.

Ultrasound can be used to measure __________, for example SONAR.

Ultrasound can be used to obtain ________, for example of a developing _______ within a mother’s womb.

Ultrasound can also be used to _______ objects.

baby scans distancefrequency cleanhuman

WORD SELECTION:

hertz

baby

scans

distance

frequency

clean

human hertz

Ultrasound Notes questions from pages 248 & 249

1. What is ultrasound? State a frequency as part of your answer.2. Copy and answer question (a) on page 248.3. (a) Describe how ultrasound is used to obtain pre-natal scans. (b)

What are the advantages of ultrasound scans over X-ray imaging? 4. How is ultrasound used in cleaning?5. Draw the diagram shown in summary question 2 and explain how

ultrasound can be used to detect flaws inside solid objects.6. Copy and answer question (b) on page 249.7. Copy the ‘Key points’ table on page 249.8. Answer the summary questions on page 249.

Ultrasound ANSWERS

In text questions:(a) The material absorbs some

of the ultrasonic sound from the loudspeaker.

(b) They do not vibrate fast enough.

(c) 30 mm from the transmitter.

Summary questions:1. (a) The organs have a different

density to the surrounding tissue. So ultrasound is reflected at the tissue/organ boundaries.

(b) Ultrasound is not ionising radiation whereas X-rays are. Ionising radiation is harmful to living tissue. Ultrasound is reflected at the boundaries between different types of tissue, whereas X-rays are not.

2. (a) Two. (b) 32-34 mm and 50 mm.

Sound SimulationsSound - PhET - This simulation lets you see sound waves. Adjust the frequency, volume, and harmonic content and you can see and hear how the wave changes. Move the listener around and hear what she hears Vend diagram quiz comparing light and sound waves - eChalk Ultrasound scanning - Explore Science

BBC KS3 Bitesize Revision: KS3 Sound Contents Page What is sound? Loudness Pitch Hearing Test bite on KS3 Sound

Light and sound issues Notes questions from pages 250 & 251

1. Answer questions 1(a), 2(a) and 2(b) on page 250.

Light and sound issues ANSWERS

1. (a) Air pollution due to dust particles, microbes in the air if hose equipment is not clean.

2. (a) To make sure the test is a fair comparison of the different materials.(b) Cushion fabric is the best absorber, soft wallpaper is next and plaster board is next. wood panel reflects sound waves more than plaster board does.