© Boardworks Ltd 2004 Waves: Sound IGCSE Physics.
-
Upload
derick-lyson -
Category
Documents
-
view
1.199 -
download
193
Transcript of © Boardworks Ltd 2004 Waves: Sound IGCSE Physics.
© Boardworks Ltd 2004
Waves: Sound
IGCSE Physics
© Boardworks Ltd 2004
Waves: Sound
Contents
What is sound?
Sound and reflection
Hearing sound
Ultrasound
Structure of sound waves
© Boardworks Ltd 2004
Aims
• Describe the production of sound by vibrating sources.
• Describe the longitudinal nature of sound waves.• Show an understanding that a medium is
required in order to transmit sound waves.• Describe an experiment to determine the speed
of sound in air.
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
Good vibrations!
What vibrates so that the following make sounds?
violin strings drum
skin
voice box
loudspeaker cone
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
Different speeds of sound
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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.
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
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!
© Boardworks Ltd 2004
Waves: Sound
Contents
What is sound?
Hearing sound
Ultrasound
Structure of sound waves
Sound and reflection
© Boardworks Ltd 2004
Aims
• Describe how the reflection of sound may produce an echo.
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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.
How does your calculation for the average speed of sound compare with the real speed?
Experiment on echoes
© Boardworks Ltd 2004
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.
© Boardworks Ltd 2004
Waves: Sound
Contents
What is sound?
Structure of sound waves
Hearing sound
Ultrasound
Sound and reflection
© Boardworks Ltd 2004
Aims
• State the approximate range of audible frequencies.
• Relate the loudness and pitch of sound waves to amplitude and frequency.
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
Wave animation
© Boardworks Ltd 2004
Waves: Sound
Contents
What is sound?
Hearing sound
Ultrasound
Structure of sound waves
Sound and reflection
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
How does the ear hear?
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
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?
© Boardworks Ltd 2004
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
© Boardworks Ltd 2004
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).
0
10
20
30
40
50
60
70
80
0 2000 4000 6000 8000
Frequency of sound [Hz]
optimalhearing
impairedhearing
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?
© Boardworks Ltd 2004
Which audiogram trace represents optimal hearing and which represents impaired hearing?
optimalhearing
impairedhearing
0
10
20
30
40
50
60
70
80
0 2000 4000 6000 8000
Frequency of sound [Hz]
optimalhearing
impairedhearing
frequency of sound (Hz)
inte
nsi
ty o
f s
ou
nd
(d
B)
Testing hearing
© Boardworks Ltd 2004
Waves: Sound
Contents
What is sound?
Hearing sound
Structure of sound waves
Sound and reflection
© Boardworks Ltd 2004
Sound multiple choice