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KS4 Physics
Using Sound
© Boardworks Ltd 2004
Learning Objectives
• Understand how sound is heard and the
audible frequencies of human hearing
• Understand how the loudness of sound is
quantified, and what is meant by “noise”
• Understand the nature and uses of
ultrasound.
• Textbook references: 6.06 (p. 134-135)
•
6.10 (p. 142-143)
Different speeds of sound
Breaking the sound barrier!
Which of these travel faster than the speed of sound in air?
distance
(m)
time
(s)
small
aeroplane
600
5
jet fighter
900
2
cheetah
50
2.5
meteorite
10 000
0.35
speed
(m/s)
The jet fighter and the meteorite break the sound barrier.
What does this mean?
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?
Echoes and reflection
What do we call reflected sound?
Are hard or soft surfaces best at reflecting sound?
How are echoes reduced in cinemas and theatres?
Name two animals that use echoes for navigation or
communication.
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
2.The waves
travel along
the ear canal.
3
5
5.The cochlea
turns these
into electrical
4.The small bones
3.The waves
signals.
(ossicles) amplify
make the ear
the vibrations.
drum vibrate.
How does the ear hear?
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?
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?
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
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?
A whisper is 30 dB and normal conversation is 60 dB.
How much more powerful is normal conversation compared
to a whisper?
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?
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.
List three ways of reducing the effects of loud noise.
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
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?
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!
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.
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.
Sound multiple choice
Learning Objectives
• Understand how sound is heard and the
audible frequencies of human hearing
• Understand how the loudness of sound is
quantified, and what is meant by “noise”
• Understand the nature and uses of
ultrasound.
• Textbook references: 6.06 (p. 134-135)
•
6.10 (p. 142-143)