KS4 Physics
Waves: Sound
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Contents
Waves: Sound
What is sound?
Sound and reflection
Structure of sound waves
Hearing sound
Ultrasound
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What causes sound?
Take a tuning fork and strike it against a block of wood.
What do you observe?
The tuning fork vibrates
and you hear a sound.
Sounds are made when
an object vibrates.
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Good vibrations!
What vibrates so that the following make sounds?
violin
strings
drum
skin
voice box
loudspeaker
cone
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How does sound travel?
How does sound reach your ear?
longitudinal wave
When the drum skin is struck, it vibrates which causes
the air beside the drum to vibrate.
The compression and stretching of air particles creates a
sound wave which is carried through the air to your ear.
What type of wave is a sound wave?
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Describe how the movement of loudspeaker
cone produces regions of high pressure
(compressions) and low
pressure(rarefactions) .
High pressure : cone moves forward or in the
direction of travel of wave OR cone pushes air
particles closer
Low pressure : cone moves backward or away
from direction of travel of wave OR cone causes
empty spaces.
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Define wavelength of sound in terms of
compressions.
Wavelength is the distance between two
successive/adjacent compressions.
Define frequency of sound in terms of
compressions.
Frequency is the number of compressions
passing a point per second.
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The bell-jar experiment
Place a ringing clock inside the bell jar and what happens?
There is air inside the bell jar
so the sound can travel and be heard.
vacuum
pump on
Remove the air from the bell jar
and what happens to the sound?
With a vacuum inside the bell jar,
the sound cannot be heard. Why?
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How fast does sound travel?
You need a quiet open space at least 100 m long
to perform this investigation.
START
STOP
00:0034
00
100 m
1. When you see the cymbals crash, press START.
2. When you hear the cymbals crash, press STOP.
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How fast does sound travel?
 Record the results of your sound experiments in a table.
sound
distance
(m)
time
(s)
speed
(m/s)
1
100
0.34
294
2
3
4
How are these values used to estimate the speed of sound?
100
distance
=
= 294 m/s
speed =
time
0.34
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How fast does sound travel?
The speed of sound in air is about…
340 m/s
 Use the results of the cymbals experiment
to calculate your average speed of sound.
How does your calculation for the average speed of sound
compare with the real speed?
What errors could have affected the results of your cymbals
experiment?
Do you think the speed of sound in water is the same
as it is in air?
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Different speeds of sound
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Sound and states of matter
Sound waves need a substance to travel through.
What are all substances made of?
solid
particles
liquid
gas
What is the particle model of a solid, a liquid and a gas?
In which state are the particles closest together? solid
In which state are the particles furthest apart?
gas
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Sound and states of matter
Sound waves travel by particles vibrating.
What state does sound travel fastest through and why?
solid
liquid
gas
Sound waves travel fastest through solids.
The particles in a solid are closer together than in a gas or
a liquid. This means vibrations are more easily passed
from particle to particle and so sound waves travels faster.
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Sound or light – which is faster?
During a thunderstorm,
thunder and lightning are
created at the same time.
Which do you notice first?
Usually, you see lightning
before you hear thunder .
Light travels much faster
than sound.
The speed of light is… 300 000 000 m/s
How much faster is light than sound?
How could you use thunder and the speed of sound
to estimate how far away a thunderstorm is?
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During a thunderstorm, the thunder was heard
3.6 s. If the speed of sound in air is 330 m/s, how
far away is the thunderstorm ?
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ASSUMPTION USED FOR THIS
CALCULATIONS
• Light travels instantaneously
• Distance of thunderstorm same as distance
travelled by sound.
• Thunder and lightening caused by same event
• Negligible wind
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Breaking the sound barrier!
Which of these travel faster than the speed of sound in air?
distance
(m)
time
(s)
speed
(m/s)
small
aeroplane
600
5
120
jet fighter
900
2
450
cheetah
50
2.5
20
meteorite
10 000
0.35
28 571
The jet fighter and the meteorite break the sound barrier.
What does this mean?
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Contents
Waves: Sound
What is sound?
Sound and reflection
Structure of sound waves
Hearing sound
Ultrasound
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Reflected sound waves
What happens when a sound wave meets a
hard flat surface?
The sound wave is reflected back from the surface.
What type of sound does this produce?
echo
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Experiment on echoes
Stand at least 100 m from a large, flat wall with a stop watch.
START
150 m
STOP
1. Use a starting pistol (or clapper board) to make a sound.
2. Measure the time taken between firing the pistol and
hearing the echo. How far does the sound travel?
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Experiment on echoes
The sound of the starting pistol takes 0.92 s
to travel a distance of 300 m.
How can you use this result to estimate the speed of sound?
distance
speed =
time
=
300
0.92
= 326 m/s
Repeat the experiment several times to obtain an average.
How does your calculation for the average speed of sound
compare with the real speed?
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METHOD 1
• Distance in field measured with tape
• One student fires pistol at one end (of this
distance)
• Student at other end starts stop-watch on
seeing smoke/light from pistol and stops stopwatch on hearing sound of pistol
• Speed =(measured)distance/(measured)time
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METHOD 2
• Distance of 50 m or more from a vertical wall
measured with tape
• Student 1 fires pistol at this from the wall
• Student 2 standing next to student 1 starts
stop-watch on hearing pistol and stops stopwatch on hearing echo
• Speed= 2 x (measured) distance / (measured)
time
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Echoes and reflection
What do we call reflected sound? an echo
Are hard or soft surfaces best at reflecting sound?
Hard surfaces produce strong echoes.
How are echoes reduced in cinemas and theatres?
By using soft materials on the walls such as curtains.
Name two animals that use echoes for navigation or
communication.
bats and dolphins
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Contents
Waves: Sound
What is sound?
Sound and reflection
Structure of sound waves
Hearing sound
Ultrasound
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Wednesday, May 1, 2024
X’teristics of sound waves
WALT
describe the characteristics
and properties of sound
waves.
Key Words
pitch
loudness
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Studying sound waves
Sound waves can be studied with this type of equipment.
loudspeaker
oscilloscope
signal generator
Which piece of equipment…
• produces signals over a range of
signal generator
frequencies and of varying amplitudes?
• converts signals into sound waves?
loudspeaker
• is used to study the frequency and
loudness of a sound?
oscilloscope
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Why sound is quiet or loud?
What is the difference between the sound wave of
a quiet sound and a loud sound?
quiet sound
loud sound
The loud sound has taller waves.
The louder the sound, the greater the amplitude.
What would the sound wave of a very loud sound look like?
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Which is the loudest?
Which trace represents the loudest sound?
A
B
Sound A is the loudest.
Sound A has the largest amplitude, which means the
wave has more energy and so the sound is louder.
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Why sound is low pitch or high pitch?
What is the difference between the sound wave of
a low pitch sound and a high pitch sound?
low pitch sound
high pitch sound
The high pitch sound has a shorter wavelength,
so more waves are visible. It has higher frequency waves.
What would the sound wave of a very low sound look like?
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Which is the highest?
Which trace represents the sound with the highest pitch?
A
B
Sound B is the highest pitched.
Sound B has the shortest wavelength and the most
number of waves visible, so it has the highest frequency.
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USING THE REPRESENTATION OF SOUND
WAVE
What would change if the sound had a higher
frequency?
Compressions and/or rarefactions closer together
OR more compressions and/or rarefactions.
What would change if the sound were louder?
Layers closer together at compressions
Layers further apart in rarefactions.
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Wave animation
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Contents
Waves: Sound
What is sound?
Sound and reflection
Structure of sound waves
Hearing sound
Ultrasound
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How does the ear hear?
1.Sound waves are
collected by the
ear lobe or
pinna.
6.The auditory nerve
takes the signals
to the brain.
6
4
1
2
3
5
2.The waves
travel along
the ear canal.
5.The cochlea
turns these
into electrical
4.The small bones
3.The waves
signals.
(ossicles) amplify
make the ear
the vibrations.
drum vibrate.
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How does the ear hear?
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Can we hear all frequencies?
Set the volume and increase the frequency of the signal
provided by the signal generator.
Humans cannot hear sounds of every frequency.
The range of frequencies you can hear is called your
hearing range.
What is the hearing range of a healthy young person?
20 Hz to 20 000 Hz
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Do we have the same hearing?
Does everyone have the same hearing range?
We all have slightly different hearing ranges
but almost 1 in 5 people suffer some sort of
hearing loss.
Temporary hearing loss may be caused by ear infections
and colds after which hearing recovers.
Permanent hearing loss and deafness can be present at
birth or occur if the ear is damaged or diseased.
People lose the ability to hear sounds of high frequency
as they get older.
Which end of their hearing range will be affected?
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Comparing hearing ranges
Do all animals have the same hearing range?
100 000
10 000
1 000
frequency
100
(Hz)
10
1
0
human
dog
bat elephant mouse dolphin
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How is loudness measured?
The loudness of a sound is measured in decibels (dB).
0 dB = quietest audible sound (near total silence)
10 dB = 10 times more powerful than the quietest sound
20 dB = 100 times more powerful than the quietest sound
How much more powerful than the quietest sound is 30 dB?
1000 times
A whisper is 30 dB and normal conversation is 60 dB.
How much more powerful is normal conversation compared
to a whisper?
1000 times
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When is sound dangerous?
Any sound above 85 dB can damage hearing.
You know you are listening to 85 dB sound
if you have to raise your voice to be heard.
What might also influence hearing loss?
The amount of time spent listening to a loud sound
also causes hearing problems.
Any 140 dB sound causes pain and immediate damage!
More than two hours of 100 dB sound can damage your ears.
Why are there laws about the maximum levels of sound
that people should be exposed to at work?
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What is noise?
A noise is any unwanted sound.
What one person considers noise another person might not.
Can you name any examples?
List three effects of noise.
headaches
nausea
deafness
List three ways of reducing the effects of loud noise.
ear protectors
double glazing
putting noisy machinery in insulated rooms
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How loud is loud?
decibels
aircraft
overhead
160
personal stereo
140
permanent
ear damage
120
100
loud
bell
80
quiet
countryside
60
40
pin being
dropped
circular saw
at 2m
20
0
can just
be heard
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How is hearing tested?
The results of a hearing tested are shown on an audiogram.
intensity of sound (dB)
80
70
loud sound
60
50
optimal
hearing
40
impaired
hearing
30
moderate sound
20
soft sound
10
0
0
2000
4000
6000
8000
Frequency of
of sound
frequency
sound[Hz]
(Hz)
low pitch
high pitch
The audiogram shows hearing sensitivity for different
frequencies (pitch) at different intensities (volume).
It records the softest sound heard at each pitch .
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Testing hearing
Which audiogram trace represents optimal hearing and
which represents impaired hearing?
intensity of sound (dB)
80
impaired
hearing
70
60
50
optimal
hearing
40
impaired
hearing
30
optimal
hearing
20
10
0
0
2000
4000
6000
8000
[Hz]
of sound
Frequencyof
frequency
sound
(Hz)
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Contents
Waves: Sound
What is sound?
Sound and reflection
Structure of sound waves
Hearing sound
Ultrasound
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Wednesday, May 1, 2024
Ultrasound
WALT
Describe some applications of
ultrasound.
Key Words
Ultrasonic
Echo-sounder
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What is ultrasound?
The upper frequency limit of human hearing 20 000 Hz.
Any high frequency sound above 20 kHz is called…
ultrasound
Whales and dolphins communicate using ultrasound.
Why does a dog whistle vibrate at ultrasound frequencies?
Can you name another human use of ultrasound?
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Using ultrasound
Which of the following does not use ultrasound?
imaging fetuses
dolphins
jewellery cleaning
ultrasonic toothbrush
viewing kidney stones
bats
ultrasonic cleaning
echo location
submarines
It’s a trick question! All of the above involve ultrasound.
High frequencies can be very useful!
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Using ultrasound in medicine
Ultrasound is the name given to a medical technique.
It uses high frequency sound waves to produce images of
inside the body without opening up the body.
fetus at 10 weeks
fetus at 20 weeks
ultrasound
for scanning
fetuses instead
of X
XWhy
raysisare
more energetic
and penetrating
and are
a rays
lot more
which would
give
a clearer
dangerous,
they
could
causepicture?
damage to the growing baby.
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How does ultrasound imaging work?
Ultrasound, like all sound, is reflected when it meets
different boundaries. So how is this used for imaging?
An ultrasound machine transmits high-frequency sound
waves into the body.
These sound waves are reflected different amounts by
different tissues.
The reflected waves are
detected by a receiver.
A computer turns the distance
and intensities of these echoes
into a two-dimensional image.
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ULTRASOUND IS PREFERRED TO X-RAY
SCAN
X-rays can cause cell damage inside a
growing baby
Ultrasound can distinguish between
different layers of soft tissue, which an
ordinary X-ray machine cannot
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NON-DESTRUCTIVE TESTING OF
MATERIALS (METAL TESTING)
• A pulse of ultrasound is sent through the metal
• If there is a flaw(tiny gap) in the metal, two
reflected pulses are picked up by the detector.
• The pulse reflected from the flaw returns first,
followed by the pulse reflected from the far end
of the metal.
• The pulses are displayed using an oscilloscope
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DISCUSS THE USE OF ULTRASOUND TO
DETERMINE THE SIZE AND POSITION OF A
BUBBLE INSIDE A METAL BLOCK
• Use of transducer to send and receive pulses
of ultrasound
• (display used to determine) time for echo of
pulse to return from front AND back of bubble.
• Use of speed of sound in the metal
• Use of distance = speed x time to calculate
position and size.
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ECHO-SOUNDING ( SONAR )
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If a pulse of ultrasound takes 0.1 s to travel to the
sea-bed and return, and the speed of sound in
water is 1400 m/s
Distance travelled = speed x time
= 1400m/s x 0.1s
= 140 m
Depth of water = ½ x 140 m = 70 m
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Sound multiple choice
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