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© Boardworks Ltd 20041 of 46
Sound
KS4 Physics
© Boardworks Ltd 20042 of 46
Sound
Contents
What is sound?
Hearing sound
Ultrasound
Structure of sound waves
Summary activities
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What causes sound?
The tuning fork vibrates and you hear a sound.
Sounds are made when an object vibrates.
Take a tuning fork and strike it against a block of wood. What do you observe?
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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?
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?
longitudinal wave
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Remove the air from the bell jar and what happens to the sound?
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.
With a vacuum inside the bell jar, the sound cannot be heard. Why?
vacuum pump on
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100 m
00:0000
START
00:0034
STOP
1. When you see the cymbals crash, press START.
2. When you hear the cymbals crash, press STOP.
You need a quiet open space at least 100 m long to perform this investigation.
How fast does sound travel?
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sound distance (m)
time(s)
speed(m/s)
1
2
3
4
How are these values used to estimate the speed of sound?
Record the results of your sound experiments in a table.
=294 m/s distance
timespeed = =
100
0.34
100 0.34 294
How fast does sound travel?
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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?
The speed of sound in air is about…
What errors could have affected the results of your cymbals experiment?
340 m/s
Do you think the speed of sound in water is the same as it is in air?
How fast does sound travel?
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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?
What is the particle model of a solid, a liquid and a gas?
In which state are the particles closest together?
In which state are the particles furthest apart?
solid
gas
particles
solid gasliquid
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Sound and states of matter
Sound waves travel by particles vibrating.
What state does sound travel fastest through and why?
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.
solid gasliquid
Sound waves travel fastest through solids.
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Usually, you see lightning before you hear thunder . Light travels much faster than sound.
The speed of light is…
During a thunderstorm, thunder and lightning are created at the same time.
Which do you notice first?
How could you use thunder and the speed of sound to estimate how far away a thunderstorm is?
300,000,000 m/sHow much faster is light than sound?
Sound or light – which is faster?
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Which of these travel faster than the speed of sound in air?
distance (m)
time (s)
speed(m/s)
small aeroplane
600 5
jet fighter 900 2
cheetah 50 2.5
meteorite 10 000 0.35
120
450
28 571
20
The jet fighter and the meteorite break the sound barrier. What does this mean?
Breaking the sound barrier!
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The sound wave is reflected back from the surface.
What type of sound does this produce?
What happens when a sound wave meets a hard flat surface?
echo
Reflected sound waves
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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?
START
150 m
Stand at least 100 m from a large, flat wall with a stop watch.
STOP
Experiment on echoes
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How can you use this result to estimate the speed of sound?
The sound of the starting pistol takes 0.92 s to travel a distance of 300 m.
=326 m/s
distance
timespeed =
=300
0.92
Repeat the experiment several times to obtain an average.
Experiment on echoes
How does your calculation for the average speed of soundcompare with the real speed?
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Echoes and reflection
What do we call reflected sound? an echo
Are hard or soft surfaces best at reflecting sound?
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
Hard surfaces produce strong echoes.
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Contents
What is sound?
Hearing sound
Ultrasound
Structure of sound waves
Summary activities
Sound
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Sound waves can be studied with this type of equipment.
loudspeaker
signal generator
oscilloscope
Which piece of equipment:
produces signals over a range of frequencies and of varying amplitudes?
converts signals into sound waves?
is used to study the frequency and loudness of a sound?
signal generator
oscilloscope
loudspeaker
Studying sound waves
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loud soundquiet sound
What is the difference between the sound wave of a quiet sound and a loud sound?
The loud sound has taller waves.
What would the sound wave of a very loud sound look like?
The louder the sound, the greater the amplitude.
Why sound is quiet or loud?
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Which is the loudest?
Sound A is the loudest.
Which trace represents the loudest sound?
Sound A has the largest amplitude, which means the wave has more energy and so the sound is louder.
A B
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low pitch sound high pitch sound
What is the difference between the sound wave of a low pitch sound and a 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?
Why sound is low pitch or high pitch?
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Which is the highest?
Which trace represents the sound with the highest pitch?
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.
BA
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Wave animation
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Contents
What is sound?
Hearing sound
Ultrasound
Structure of sound waves
Summary activities
Sound
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1.Sound waves are collected by the ear lobe or pinna.
2.The waves travel along the ear canal.
3.The waves make the ear drum vibrate.
4.The small bones (ossicles) amplify the vibrations.
5.The cochlea turns these into electrical signals.
6.The auditory nerve takes the signals
to the brain.
3
4
5
6
1
2
How does the ear hear?
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How does the ear hear?
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Set the volume and increase the frequency of the signal provided by the signal generator.
20 Hz to 20,000 Hz
Humans cannot hear sounds of every frequency.
What is the hearing range of a healthy young person?
The range of frequencies you can hear is called your hearing range.
Can we hear all frequencies?
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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.
Does everyone have the same hearing range?
People lose the ability to hear sounds of high frequency as they get older.
Which end of their hearing range will be affected?
Do we have the same hearing?
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100,000
10,000
1,000
100
10
1
0
human dog elephantbat mouse dolphin
Do all animals have the same hearing range?
frequency(Hz)
Comparing hearing ranges
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A whisper is 30 dB and normal conversation is 60 dB.
How much more powerful is normal conversation compared to a whisper?
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
1,000 times
1,000 times
How much more powerful than the quietest sound is 30 dB?
How is loudness measured?
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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.
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.
What might also influence hearing loss?
Why are there laws about the maximum levels of sound that people should be exposed to at work?
When is sound dangerous?
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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.
nausea
headaches
deafness
List three ways of reducing the effects of loud noise.
ear protectors
putting noisy machinery in insulated rooms
double glazing
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160
140
120
100
80
60
40
20
0
permanent ear damage
can just be heard
aircraft overhead
decibels
circular saw at 2m
quiet countryside
pin being dropped
loud bell
personal stereo
How loud is loud?
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The results of a hearing tested are shown on an audiogram.
It records the softest sound heard at each pitch .
The audiogram shows hearing sensitivity for different frequencies (pitch) at different intensities (volume).
frequency of sound (Hz)
inte
nsi
ty o
f so
un
d (
dB
)
loud sound
moderate sound
soft sound
low pitch high pitch
How is hearing tested?
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Which audiogram trace represents optimal hearing and which represents impaired hearing?
optimalhearing
impairedhearing
frequency of sound (Hz)
inte
nsi
ty o
f s
ou
nd
(d
B)
Testing hearing
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Contents
What is sound?
Hearing sound
Ultrasound
Structure of sound waves
Summary activities
Sound
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The upper frequency limit of human hearing 20,000 Hz.
Any high frequency sound above 20 kHz is called…
Whales and dolphins communicate using ultrasound.
Why does a dog whistle vibrate at ultrasound frequencies?
Can you name another human use of ultrasound?
ultrasound
What is ultrasound?
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dolphins
ultrasonic toothbrush
jewellery cleaning
imaging fetuses
submarines
viewing kidney stones
echo location
bats
ultrasonic cleaning
Which of the following does not use ultrasound?
It’s a trick question! All of the above involve ultrasound.High frequencies can be very useful!
Using ultrasound
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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.
X rays are more energetic and penetrating and are a lot more dangerous, they could cause damage to the growing baby.
fetus at 10 weeks fetus at 20 weeksWhy is ultrasound used for scanning fetuses instead ofX-rays, which would give a clearer picture?
Using ultrasound in medicine
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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.
How does ultrasound imaging work?
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Contents
What is sound?
Hearing sound
Ultrasound
Structure of sound waves
Summary activities
Sound
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Glossary
amplitude – How loud a sound is, which depends on the height of the peak of a sound wave from its rest position.
audiogram – A graphical recording of hearing ability at various sound frequencies.
echo – The sound produced when sound waves are reflected from a surface and heard shortly after the original.
frequency – The number of waves per second, which shows the pitch of a sound. It is measured in hertz (Hz).
oscilloscope – A device that displays electronic signals (waves and pulses) on a screen.
pitch – How high a sound is, which depends on the frequency of the sound wave vibrations.
ultrasound – Sound waves with very high frequencies above the range of human hearing, which are used forproducing images of inside the body.
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Anagrams
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Sound multiple choice