AQA GCSE 3-2B
Sound
GCSE Physics pages 244 to 251
April 10th 2010
AQA GCSE Specification
SOUND
13.5 What is sound?
ULTRASOUND
13.6 What is ultrasound and how can it be used?
Using skills, knowledge and understanding of how
science works:
• to compare the amplitudes and frequencies of sounds
from diagrams of oscilloscope traces.
Using skills, knowledge and understanding of how
science works:
• to compare the amplitudes and frequencies of
ultrasounds from diagrams of oscilloscope traces
• to determine the distance between interfaces in
Skills, knowledge and understanding of how science
works set in the context of:
• Sound is caused by mechanical vibrations and travels
as a wave.
• Sounds in the range 20-20 000 Hz can be detected by
the human ear.
• Sound cannot travel through a vacuum.
• The pitch of a note increases as the frequency
increases.
• The loudness of a note increases as the amplitude of
the wave increases.
• The quality of a note depends upon the waveform.
• Sound waves can be reflected and refracted.
Skills, knowledge and understanding of how science
works set in the context of:
• Electronic systems can be used to produce ultrasound
waves which have a frequency higher than the
upper limit of hearing for humans.
• Ultrasound waves are partially reflected when they
meet a boundary between two different media. The
time taken for the reflections to reach a detector is a
measure of how far away such a boundary is.
• Ultrasound waves can be used in industry for cleaning
and quality control.
• Ultrasound waves can be used in medicine for prenatal scanning.
Sound
Sound is produced by vibrating objects.
LONGITUDINAL WAVE
A sound wave consists of mechanical
vibrations in air and other substances.
wave direction
vibrations
Sound is a longitudinal wave in which the
wave energy travels in the same direction
as the particles within the wave vibrate.
TRANSVERSE WAVE
Most other types of wave are transverse.
For examaple water and light waves. In
these cases the particles making up the
wave vibrate at ninety degrees to the
direction of energy transfer.
vibrations
wave direction
Through air a sound wave consists of a series of
compressions and rarefactions.
A compression is a region of slightly higher
pressure where the air molecules are closer
together than usual.
A rarefaction is the opposite.
compression
loudspeaker
no
sound
wave
sound
wave
wavelength
rarefaction
Speed of sound
Substance
Speed in m/s
Air at 0ºC
330330
Air at 20ºC
342342
Water at 20ºC
1 500
1 500
Steel at 20ºC
5 000
5 000
Sound does not travel through a vacuum.
In space no one can hear you scream!
– tagline of the film Alien (1979)
Question
A thunderclap is heard 12 seconds after a lightning
flash. Calculate the distance to the lightning flash.
Take the speed of sound = 340 m/s
speed = distance / time
becomes: distance = speed x time
= 340 m/s x 12 seconds
= 4 080 m
Distance = 4.08 km
Bell jar experiment
This experiment shows that sound
needs a material medium for
transmission.
As the air pressure inside the bell
jar is reduced the loudness of the
sound heard outside decreases.
The bell can be still seen to be
working normally.
Range of hearing
Humans can hear sounds in the range 20 Hz to 20 000 Hz.
Age and damage reduces the upper limit.
For example an old person or someone exposed to perlonged high
sound volume may no be able to hear above 10 000 Hz.
Some animals can hear much higher frequencies:
dogs – 40 000 to 60 000 Hz (depends on the breed)
bats and dolphins – 100 000 Hz
Reflection of sound
An echo is a reflected sound wave.
Question:
A missguided child shouts ‘Chelsea!’ at
a nearby cliff and hears their echo 1.4 s
later. How far away is the cliff?
Take the speed of sound = 340 m/s.
distance, D
The sound travels to and from the cliff, a total distance of 2D
speed = distance / time
becomes: distance = speed x time
= 340 m/s x 1.4 s
= 476 m
= 2D !
Therefore distance to the cliff = 238 m.
Sound refraction
C
A
B
cooler air
The sound produced by person A may be heard more clearly by
person B than by person C.
The cooler air over the water refracts the sound waves downwards.
Sound
Notes questions from pages 244 & 245
1.
2.
3.
4.
5.
6.
7.
8.
(a) What type of objects produce sound waves? (b) What is the
typical range of frequencies audible to a young person? (c) How
does this range change with age?
Draw a diagram and describe an experiment to show that sound
waves do not travel through a vacuum.
Draw Figure 1 on page 244 and explain the difference between
longitudinal and transverse waves. State which type is sound.
(a) What is an echo? (b) How are echoes affected by the surface
of materials?
Why does sound travel better at night?
Copy and answer questions (a), (b), (c), (d) and (e) on pages 244
and 245.
Copy the ‘Key points’ table on page 245.
Answer the summary questions on page 245.
Sound
ANSWERS
In text questions:
(a) A mouse.
(b) The sound becoming
audible again.
(c) Wave one end from side to
side.
(d) There are no reflections, so
each note dies away more
quickly outdoors.
(e) Colder.
Summary questions:
1. (a) Reflected.
(b) Scattered, absorbed.
(c) Refracted.
2. (a) About 18000 Hz
(b) The vibrating surface of the
loudspeaker pushes the air
near it to and fro, creating
sound waves which spread out
from the loudspeaker.
(c) The ball inside goes
around at constant speed and
makes the surrounding air
vibrate.
Sound waves on oscilloscopes
An oscilloscope is a
device that can be
used to display a
sound wave.
The screen displays a
graph of how the
amplitude of the sound
wave varies with time.
Loudness
The loudness of a sound increases with the
amplitude of the sound wave.
quiet
loud
Pitch
The pitch of a musical note increases with frequency.
low pitch
high pitch
Examples:
Concert pitch A = 440 Hz; Top C = 523 Hz
Doubling the frequency increases the pitch by one octave.
Therefore the ‘A’ above top C will have frequency 880 Hz.
Quality
The quality or timbre of a musical note is what makes one
musical instrument sound different from another.
Despite different instruments producing a note of the same
loudness and pitch, the shape of the wave will be different.
Question
The diagram opposite
shows the appearance of a
sound wave on an
oscilloscope. Draw a
second diagram showing
the appearance of a sound
wave of lower pitch but
greater loudness.
Question
Choose appropriate words to fill in the gaps below:
longitudinal wave that in air consists of a series of
Sound is a ___________
rarefactions
compressions and _____________.
solids
Sound travels fastest through _______
but does not travel at
vacuum
all through a __________.
reflected
A ____________
sound wave is called an echo. Sound also
refraction
undergoes ___________.
amplitude
The loudness of a sound increases with wave __________,
the
frequency
pitch with wave ____________.
WORD SELECTION:
rarefactions refraction vacuum amplitude solids
longitudinal reflected frequency
Musical sounds
Notes questions from pages 246 & 247
1.
2.
3.
4.
5.
6.
7.
Explain the difference between a musical note and noise.
Draw wave diagrams to explain what happens when there is
an increase in a sound wave’s (a) loudness and (b) pitch.
Copy and answer questions (a), (b) and (c) on pages 246
and 247.
Explain how the three main categories of musical instrument
produce sound.
Why do different musical instruments producing the same
note sound different from each other? Illustrate your answer
with a waveform diagram.
Copy the ‘Key points’ table on page 247.
Answer the summary questions on page 247.
Musical sounds
ANSWERS
In text questions:
(a) An ambulance, a police vehicle,
a fire engine, an ice cream van.
(b) The waves are not as tall.
(c)
The waves would be smaller in
height and stretched out more.
Summary questions:
1. (a) The waves would be taller but
would have the same spacing.
(b) The waves would be more
stretched out but would have the
same height.
2. (a) (i) The note has a higher pitch
(frequency).
(ii) The note has a higher pitch
(frequency).
(b) The sound of a violin (played
correctly) lasts as long as the
violin bow is in contact with a
string. The sound of a drum dies
away after the drum skin has been
struck. A drum note is less
rhythmical than a violin note.
Ultrasound
Ultrasound is very high frequency sound that is
above 20 000 Hz, too high to be heard by humans.
Some animals, for example dogs, bats and
dolphins can communicate or navigate using
ultrasound.
Ultrasound echoes can be used to measure
distance (e.g. sonar) and to see inside objects
(scans).
Sonar
SOund Navigation And Ranging.
Ultrasound scans
Ultrasound waves are partially reflected when they
meet a boundary between two different media. The
time taken for the reflections to reach a detector is
a measure of how far away such a boundary is.
Ultrasound reflects off
each tissue boundary
Ultrasound
transmitter
Developing
baby
1. Prenatal scanning
2. Quality control
Ultrasonic testing is a
type of nondestructive
testing commonly
used to find flaws in
materials and to
measure the
thickness of objects.
At a construction site, a
technician tests a pipeline
weld for defects using an
ultrasonic instrument.
Question
The oscilloscope trace opposite was
obtained from the scan of a metal
block.
(a) how many flaws are present
according to this display?
(b) If the width of the block was 300
mm calculate the distance fro the front
of the block to each flaw.
(a) There are two flaws.
(b) The width of the block is
represented by 8.3 squares.
Therefore each square represents
300mm / 8.3
= 36.1 mm per square
The two flaws occur after 3.0 and 4.2
squares
Therefore:
1st flaw is at 3.0 x 36.1
= 108 mm from the front
2nd flaw is at 4.2 x 36.1
= 152 mm from the front
Ultrasound cleaning
The very high frequency waves of ultrasound can
be used to shake off dirt or grease.
Another way of cleaning teeth
Jewellery immersed in water
Question
Choose appropriate words to fill in the gaps below:
frequency
Ultrasound is very high ___________
sound. It is above the
hertz
human
upper range of _________
hearing, more than 20 000 _______.
distance
Ultrasound can be used to measure __________,
for example
SONAR.
scans
Ultrasound can be used to obtain ________,
for example of a
baby within a mother’s womb.
developing _______
clean objects.
Ultrasound can also be used to _______
WORD SELECTION:
baby human scans frequency distance clean hertz
Ultrasound
Notes questions from pages 248 & 249
1.
2.
3.
4.
5.
6.
7.
8.
What is ultrasound? State a frequency as part of your answer.
Copy and answer question (a) on page 248.
(a) Describe how ultrasound is used to obtain pre-natal scans. (b)
What are the advantages of ultrasound scans over X-ray imaging?
How is ultrasound used in cleaning?
Draw the diagram shown in summary question 2 and explain how
ultrasound can be used to detect flaws inside solid objects.
Copy and answer question (b) on page 249.
Copy the ‘Key points’ table on page 249.
Answer the summary questions on page 249.
Ultrasound
ANSWERS
In text questions:
(a) The material absorbs some
of the ultrasonic sound from
the loudspeaker.
(b) They do not vibrate fast
enough.
(c) 30 mm from the transmitter.
Summary questions:
1. (a) The organs have a different
density to the surrounding
tissue. So ultrasound is
reflected at the tissue/organ
boundaries.
(b) Ultrasound is not ionising
radiation whereas X-rays are.
Ionising radiation is harmful to
living tissue. Ultrasound is
reflected at the boundaries
between different types of
tissue, whereas X-rays are not.
2. (a) Two.
(b) 32-34 mm and 50 mm.
Sound Simulations
Sound - PhET - This
simulation lets you see
sound waves. Adjust the
frequency, volume, and
harmonic content and you
can see and hear how the
wave changes. Move the
listener around and hear
what she hears
Vend diagram quiz
comparing light and sound
waves - eChalk
Ultrasound scanning Explore Science
BBC KS3 Bitesize Revision:
KS3 Sound Contents Page
What is sound?
Loudness
Pitch
Hearing
Test bite on KS3 Sound
Light and sound issues
Notes questions from pages 250 & 251
1. Answer questions 1(a), 2(a) and 2(b) on
page 250.
Light and sound issues
ANSWERS
1. (a) Air pollution due to dust particles, microbes
in the air if hose equipment is not clean.
2. (a) To make sure the test is a fair comparison
of the different materials.
(b) Cushion fabric is the best absorber, soft
wallpaper is next and plaster board is next.
wood panel reflects sound waves more than
plaster board does.