Transcript Sound and Hearing

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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.
All sounds are caused
by vibrations.
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Music
What vibrates when you sing?
Your voice-box.
What vibrates when you play a violin?
The strings
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The Bell-jar experiment
What happens when the air is removed from the bell-jar?
 Sound waves are vibrations and so need a substance
to travel through.
 With air inside, the sound can be heard.
With nothing inside [a vacuum], the sound can’t be heard.
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Sound : How fast does it travel?
 You need a quiet open space at least 100m long to
perform this investigation.
STOP
START
00:0000
34
> 100m
1) When you see the cymbals crash, press START.
2) When you hear the cymbals crash, press STOP.
 Write your results in a table like this:
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Sound : How fast does it travel?
Try
Distance
[m]
Time
[s]
Speed
[m/s]
1.
100
0.34
294
2.
3.
4.
 Calculate your average speed of sound :
Av. = [try 1 + try 2 + try 3 + try 4]  4.
 What errors could have crept into your results?
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Sound : How fast does it travel?
 Sound waves need particles in order to travel.
 The substance that the sound travels through affects the
speed of sound greatly.
7000
6000
6000
5000
5000
4000
3000
2000
1450
1000
330
350
Air at 0 C
Air at 30 C
0
W ater
Concrete
Steel
Material
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Travelling sound
Sound travels by particles vibrating. To understand this
better you need to remember what the particles look
like in a solid, liquid and a gas:
solid
liquid
gas
Which state does sound travel fastest through? Why?
In
whichtravels
state are
the particles
closest
together?
solid
Sound
fastest
through solids
because
the particles
are closer together than in a liquid and a gas, so the
vibrations
are are
more
passed
fromapart?
particle to particle.
In
which state
theeasily
particles
furthest
gas
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Sound : How fast does it travel?
 Most of us have seen
thunder storms - which comes
first, the thunder or lightning?
 The lightning gets to our
eyes before the thunder
reaches our ears.
1)
Thunder & lightning are made at the same time so we
deduce that light travels much faster than sound.
2)
In fact light travels so fast that:
the time between seeing the flash and hearing the bang =
time taken for sound to travel.
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Reflection : echoes
 You should remember that sound is produced by a
vibration and travels as a longitudinal wave
………..and that sound travels at different speeds through
different substances [or media]
 Sound waves reflect
off hard, smooth surfaces
to produce echoes
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Using echoes
What do we call reflected sound?
an echo
Which surfaces are the best at reflecting sound:
HARD or SOFT ?
How are echoes reduced in cinemas and theatres?
By using soft materials on the walls such as curtains.
Name two animals that use echoes?
Bats and Dolphins
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Reflection : Echoes
 Stand at least 100m
from a large, straight
wall
150m
 Measure the distance
from you to the wall
 Use a starting pistol
[or clapper board] to
make a sound
 Measure the time
taken between firing the
pistol and hearing the
echo
START
STOP
 Remember, this is
‘two way travel time’ [twtt]
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Reflection : Echoes
 The sound takes 0.92s to travel 300m
 Remember the formula for speed?
SPEED = DISTANCE  TIME
v
=
300
 0.92
v
=
326 m/s
 Repeat this several times to obtain an average
 For the Higher Tier paper you will need to be able to
change the subject of the formula
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Reflection : questions
Distance
[m]
Time
[s]
Small
aeroplane
600
5
120
 Jet fighter
900
2
450
 Meteorite
10,000
0.35
50
2.5
Cheetah
Speed
[m/s]
28571
20
Which of these travel faster than the speed of sound in air?
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Studying sound
Loudspeakers convert
the signal from the
signal generator into
sound waves.
The oscilloscope
allows us to study the
frequency and
loudness of a sound.
Signal generators can
produce signals over a range
of frequencies and of varying
amplitudes.
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Pitch (or frequency)
 A high pitch sound.
 A low pitch sound.
The shorter/longer the wavelength of the
wave on the trace; the lower/higher the
frequency of the sound.
The more waves you can see, the higher
the pitch/frequency.
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Oscilloscope traces
Which trace represents the highest pitched sound?
A
B
‘A’ is the highest pitched sound because it has the
shortest wavelength/most number of waves visible.
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Loudness
 A quiet sound.
 A louder sound.
The larger/smaller the amplitude of the wave on the
trace, the louder/quieter the sound.
The bigger the waves you can see, the louder the sound.
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Oscilloscope traces
Which trace represents the loudest sound?
A
B
‘B’ Is the loudest sound because it has the largest
amplitude.
The larger the amplitude the more energy a wave has.
The more energy it has, the louder the sound.
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Wave animation
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Sound : What can I hear?
 Increase the frequency of the signal provided by a
signal generator whilst keeping the volume the same.
20 Hz
 The lowest frequency I can hear is ________
20 000 Hz
 The highest frequency I can hear is ________
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Sound : Are we all the same?
 You have just found your hearing range - could
everyone hear exactly the same frequencies as you?
We all have slightly different hearing ranges but almost
1 in 5 people suffer some sort of hearing loss. This
changes with age. A baby has a wider range than an older
person.
 Temporary hearing loss may be caused by ear
infections and colds and hearing recovers.
 Permanent hearing loss and deafness can be present
at birth or occur if the ear is damaged or diseased.
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Sound : Are we all the same?
 Hearing is tested using an audiometer and the results
are shown on an audiogram.
80
70
Hearing Loss [dB]
60
50
optimal
hearing
40
impaired
hearing
30
20
10
0
0
2000
4000
6000
8000
Frequency of sound [Hz]
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Sound : Hearing Ranges
Hearing Ranges of Animals
Bats
Pigeons
Humans
Mice
Elephants
Moths
1,000,000
100,000
10,000
1,000
100
10
1
0
Which animal
animal can
can
Which
hear the
thehighest
lowest
hear
frequency?
frequency?
Frequency [Hz]
moths
pigeons
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Sound : The ear
1. Sound
waves are
collected
by the ear
lobe or
pinna.
3. The waves
2. The waves
travel along the make the ear
drum vibrate.
ear canal.
6. The
auditory
nerve
takes the
signals to
the brain.
4. The
small bones
[ossicles]
amplify the
vibrations.
5. The
cochlea turns
the vibrations
into electrical
signals.
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Sound : The ear
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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Sound : The ear
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Sound : How loud are sounds?
Aircraft overhead 150
140
120
Personal stereo
Permanent
ear damage
Loud bell
100
A circular saw at 2m
80
60
40
Quiet countryside
20
Pin being dropped
10
0
Can just be heard
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What is noise?
A noise is any unwanted sound.
What are the effects of noise?
What you might not
consider noise, loud
music for example,
other people might.
1.
Deafness
_________
2.
Vomiting
_________
3.
Headaches
_________
How can you reduce the
effects of loud noise?
4.
Nausea
_________
1. _________________
Ear protectors
Double glazing
2. _________________
Putting noisy machinery in
3. ___________________
insulated rooms
_______________
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What is the upper range of human
hearing?
A. 20 Hz
B. 200 Hz
C. 2 000 Hz
D. 20 000 Hz

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What causes all sounds?
A. Vibrations

B. Reflections
C. Refractions
D. Heat
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Which of the following can sound not
travel through?
A. Liquid
B. Vacuum

C. Solid
D. Gas
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A ship releases an echo sounding and 4
seconds later receives a signal from the
seabed, how deep is the sea? (speed of
sound in water is 1500 m/s)
A. 6000m
B. 375m
C. 750m
D. 3000m

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Which of the following is not a use of
ultrasound?
A. Prenatal scanning
B. Quality control in industry
C. Cleaning delicate machinery
D. Cooking food

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