Turnbull High School
Physics Department
CfE
National 4 /National 5
Physics
Unit 1
Waves and Radiation
Section 2: Sound
Name:
Class:
1
National 4
Unit 1: Section 2
By the end of Unit 1 Section 2:
• I can analyse sound waveforms including changing
amplitude and frequency.
• I can measure sound levels using a sound level meter
and state some common sound levels on the decibel
scale
• I can explain what noise pollution is and the risks it can
cause to human hearing.
• I can identify methods of protecting hearing
• I know the range of frequency for human hearing
• I can describe applications of sonar and ultrasound
• I can describe a basic system for sound reproduction
technology
• I can explain the simple idea behind noise cancellation
and give an application of it’s use.
2
Unit 1: Section 2
By the end of Unit 1 Section 2
I will have:
• Carried out an investigation involving sound.
• Produced a power point on a chosen subject in relation
to sound and presented it to my class.
3
Sound Waves: Vibrations
Experiment 1
Take a look at the various instruments in the classroom. Try them
out. How is the sound produced?___________________________
___________________________________________________
Musical instruments
produce sound when part
of the instrument
___________.
A guitar string ___________ when it is
plucked.
A trumpet blasts out sound when the _____ inside it vibrates.
______________ is transferred from the vibrating object to the
listener by ____________ waves which travel through the air.
These ___________ waves make the air vibrate. The vibrations
pass into our ears.
Frequency
Each note or sound has a frequency which is measured in _____(Hz).
From section 1 we know that:
Frequency is the number of ______ produced per _______.
A tuning fork will have its frequency value engraved on it. If a tuning
fork has a frequency of 256 Hz, this means that ________ sound
waves are produced every ___________.
A whistle produces a higher frequency sound than a vibrating drum.
The whistle has a higher ___________. The higher the pitch, the
higher the _____________.
4
Sound and energy
In order for us to hear a sound something must make our eardrums
move. You may remember from first year that all moving objects
have kinetic energy. Energy must be transferred to our ears. Sound
waves carry this energy through the air.
Sounds travel away from the source like
ripples on a pond. The further from the source
you are the less energy reaches you. This is
why if you are too far from a sound you cannot
hear it. A person can probably only shout over
a distance of around 100m before the sound
gets too quiet to hear.
When the volcanic island of
Krakatoa erupted it generated the
loudest sound ever historically
reported — the massive explosion
was distinctly heard as far away
as the island of Rodrigues near
Mauritius (approx. 3000 miles or
4800 km). This is like us hearing
an explosion that happened in New
York.
Nowadays if someone is a bit hard of hearing there are electronic
hearing aids that they can wear. These are really like miniature
tannoy systems. They have a microphone which picks up sounds and
changes them into electrical signals, an amplifier which gives energy
to the signal and a loudspeaker which changes the amplified
electrical signal back into sound and sends the sound into the ear.
5
In the olden days before electronics people
used to make use of ear trumpets to help
them hear. The ear trumpet collected sound
waves and passed them down a tube into the
person’s ear. This is a bit like the satellite dish collecting radio
signals and reflecting them to the aerial.
Answer the following questions in sentences:
1. What must happen for us to hear a sound?
_______________________________________________
2. What do sound waves carry through the air?
_______________________________________________
3. What was the loudest sound ever historically reported?
_______________________________________________
4. Jeremy is hard of hearing. Write a short note to Jeremy to
explain what he could do improve his hearing.
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
6
Sound Travelling Through Materials (Revision)
Can sound travel through:
solids like brick
Yes/No
liquids like water?
Yes/No
gases like air?
Yes/No
Experiment 2
Your teacher will demonstrate the bell jar experiment to you.
With the bell ringing the air is gradually removed from the bell jar
(a vacuum is created). Listen carefully!
Sound cannot travel through a v _ _ _ _ _ where there are no
s _ _ _ _, l _ _ _ _ _ or g _ _ particles.
When the jar has air in it, we can hear the bell r _ _ _.
Sound can travel through __________, __________ and
__________.The only place that sound cannot pass through is a
________________.
A vacuum is an _____________ space, so there are no
____________ to pass on the sound vibrations.
7
Detecting sound
Sound can be detected by a ____________ or produced by a
signal generator and a trace displayed on an oscilloscope.
A m_________ changes s____ energy into e_________ energy.
A l__________ changes e_________ energy back into s______
energy.
Experiment 3
Oscilloscope patterns: Loudness
Aim:
To investigate how sounds vary in loudness.
Instructions
• Your teacher will adjust the volume control on the signal
generator.
8
• Copy the diagrams shown below and draw the pattern produced
on the oscilloscope for :
(i)
(ii)
the quietest sound played
the loudest sound played
What happens to the pattern on the oscilloscope when a louder
sound is produced?____________________________________.
The amplitude of a wave is the distance from the ____________ of
the wave to the top or the bottom of the wave.
A loud sound transfers more ___________ so the oscilloscope
trace will have a ____________ amplitude.
A quiet sound transfers less ___________ so the oscilloscope trace
will have a ____________ amplitude.
9
Experiment 4
Oscilloscope patterns: Frequency
Aim: To investigate how sounds vary in pitch.
Instructions:
In section 1 you learned that frequency is the number of waves
produced per second. Frequency is measured in Hertz (Hz).
• Your teacher will adjust the signal generator so that different
notes are ‘played’.
• Copy the diagrams shown below and draw the pattern produced
on the oscilloscope for
(iii)
the highest frequency played
(iv)
the lowest frequency played
If the frequency is higher, _________ waves can be seen on the
screen. The higher the frequency of a note the higher it’s ______.
10
Sound Levels
Some sounds are louder than others. We can measure the loudness
of a sound using a sound level meter. We measure the loudness of
sound in units called d _ _ _ _ _ _ _ ( _ _ ).
Experiment 5
Your teacher will show you how to operate a sound level meter.
Using your sound level meter measure readings for the following
situations and record them in the table below:
Situation
A quiet classroom
1m from a radio
1m from a person talking
A noisy area
1m from an electric bell
1m from a person shouting
1m from loudspeaker
Sound level (dB)
11
Match the sound levels given below to the correct situation.
12
Tutorial 1
1. An orchestra has various sections – like string, brass, percussion,
etc.
(a) How do all musical instruments produce sound energy?
_____________________________________________________
(b) Complete the following:
Sound is a ______ which transfers ________.
2. (a)
(b)
Frequency is measured in
A
Watts
B
Decibels
C
Hertz
D
Volts
Frequency is
A The number of waves produced in one second.
B The number of waves produced in one minute.
C The number of waves produced in total.
3.
An oscilloscope can display a musical note on the screen.
a) How many waves are seen on the screen?___________________
b) The frequency of these waves is 50Hz. How many waves are produced
in one second?_______________________________________
c) What is the period of these waves?
13
4. Jane uses a signal generator to increase the pitch of the note emitted in
question 3. The signal generator has an amplitude control and a frequency
control.
a) Which control did Jane turn?
Jane now connects an oscilloscope to the generator and adjusts the amplitude
and frequency controls.
b) What did Jane do to the loudness of the note emitted? Explain your
answer.
____________________________________________________
____________________________________________________
c) What did she do to the frequency of the note? Explain your answer.
____________________________________________________
____________________________________________________
5.
(a) Copy and complete the following sentence
Sound levels are measured in ____________.
b) Match up the sound levels with their source.
Sound level in dB
Source
0
Jet engine
20
Normal conversation at 1m
30
Threshold of pain
60
Silence
90
Heavy truck
130
Quiet country lane
140
Tick of a watch
14
Noise Pollution
Noise pollution is any s _ _ _ _ which is unpleasant to h _ _ _
(usually above 90 dB)
Some examples of noise pollution are:
______
_______
________
_______
Risks to hearing
Some people are exposed to long periods of loud sounds
(e.g. factory workers, engineers, airport workers,
musicians etc.). Regular exposure to sounds above 90
dB can cause damage the tiny hair cells in the inner ear
or to the ear drum and cause permanent damage to
hearing. To prevent this some form of ear protection
should be used. For example:
Earplugs, earmuffs, headphones, helmet, noise-cancellation
devices etc.
What can happen to people who are
exposed to too much loud noise for a long
period of time?
___________________________________________________
___________________________________________________
___________________________________________________
15
Noise-cancelling headphones
Noise-cancelling headphones are any headphones that reduce
unwanted ambient sounds (i.e., acoustic noise) by means of active noise
control (ANC). This involves using one or more microphones placed near
the ear, and electronic circuitry which uses the microphone signal to
generate an "anti-noise" signal. When the anti-noise signal is produced by the
speaker driver in the headphone, destructive interference cancels out the
ambient noise as heard within the enclosed volume of the headphone. They
should not be confused with noise isolating headphones.
Noise cancellation makes it possible to enjoy music without raising the volume
excessively. It can also help a passenger sleep in a noisy vehicle such as an
airliner.
Noise-cancelling headphones typically use ANC to cancel the lower-frequency
portions of the noise; they depend on more traditional methods such as
soundproofing to prevent higher-frequency noise from reaching the ear. This
approach is preferred because it reduces the demand for complicated
electronic circuitry that would be required for noise cancellation at higher
frequencies, where active cancellation is less effective. To truly cancel high
frequency components (coming at the ear from all directions), the sensor and
emitter for the cancelling waveform would have to be adjacent to the user's
eardrum, which is not always technically feasible.
Now answer the following questions:
1. Explain how noise-cancelling headphones reduce unwanted
sounds.
_______________________________________________
_______________________________________________
_______________________________________________
2. What advantages are there to noise cancellation?
_______________________________________________
_______________________________________________
_______________________________________________
3. Active noise cancellation (ANC) is most effective for low
frequency sounds. How are high frequency sounds blocked?
_______________________________________________
_______________________________________________
16
The Range of Human Hearing
Experiment 6
Using the apparatus below you will be measuring the upper and lower
threshold frequency of your own hearing:
Lowest frequency I can hear =
Highest frequency I can hear =
When listening to music, you hear sounds of many frequencies.
Humans can detect frequencies between __________ and
__________ Hz. These are audible frequencies for humans.
As we get older, the upper limit gradually _____ to about 15 000Hz.
Some animals can detect higher frequency sounds than humans,
e.g. _______________ and _______________.
17
Ultrasound
Sound with a frequency of vibration ________the upper limit of
human hearing (________ Hz) is called ultrasound.
• Read the following information.
‘As blind as a bat’ is a common saying. Bats are almost blind, but
they can locate obstacles or insects by using very high frequency
sound waves. Humans can hear frequencies up to 20 000Hz.
Higher frequencies than this are called Ultrasounds. When these
higher frequency waves are sent out and hit an object
some are reflected like an echo. Bats
use these echoes to find their way
around.
Ultrasounds are used in medicine to
scan unborn babies. This is a safe way to monitor the
growth and health of an unborn baby. Ultrasounds are sent out
from a transmitter and are reflected back from the baby to a
detector. A picture or scan can then be viewed on a computer
screen.
Ultrasound can also be used in medicine to
destroy kidney stones. The
Fishermen also use ultrasounds at sea to locate
shoals of fish. Ultrasounds are sent out and
reflected by the sea bed. If there are fish in the way, the
ultrasounds will reflect from them and be detected back at the
boat more quickly.
18
Questions
1.
What is ultrasound?
_______________________________________________
_______________________________________________
2.
Explain how ultrasounds can be used in medicine.
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
3.
Explain one non-medical use of ultrasounds.
_______________________________________________
_______________________________________________
_______________________________________________
_______________________________________________
4.
Sonar consists of sound waves that reflect from the sea bed
or objects under the sea. A sonar pulse was sent down from a
ship looking for a shoal of fish and two pulses were reflected
back, the first after 0.85s and the second after 2.3 seconds.
If the speed of sound in water is 1500 m/s:
(a)
Calculate the depth of the water.
(b)
Calculate the depth at which the fish are swimming.
19
Sound reproduction systems
Amplifiers play an important part in electronic sound reproduction
systems which have a loudspeaker output - For example:
________________________________________________
________________________________________________
Experiment 7
Your teacher will demonstrate the amplifier circuit below:
The amplifier increases the a _ _ _ _ _ _ _ _ of the electrical
i _ _ _ _ signal.. As a result, the o _ _ _ _ _ signal has a greater
amplitude than the input signal - It now has enough e _ _ _ _ _ to
power the loudspeaker.
loudspeaker
For example, a karaoke machine:
The audio amplifier does not change the f _ _ _ _ _ _ _ _ of
the input signal - If the input signal has a frequency of
1 000 Hz, the output signal has a frequency of _______ Hz.
Hz
The trace below shows the electrical signal from a microphone which
is being input to an amplifier.
amplifier. On the same trace, draw the possible
shape of the output signal.
signal
20
Voltage Gain of an Amplifier
In an electronic system, the electrical signals are usually voltages.
The number of times an amplifier increases the amplitude of an
input voltage by is known as the v _ _ _ _ _ _ g _ _ _ of the
amplifier.
Gain = Vout
Vin
Experiment 8
Set up the apparatus shown below:
Without changing the settings on the amplifier gradually increase
the input voltage. For each input voltage note down the output
voltage in the table below:
Vin
Vout
Vin / Vout
The voltage gain of my amplifier is ____________.
21
Problems on Voltage gain
1. In each case below, calculate the voltage gain of the amplifier:
(a)
input voltage = 12 V,
output voltage = 36 V
(b)
input voltage = 2.5 V,
output voltage = 75 V
(c)
input voltage = 1.2 V,
output voltage = 24 V
(d)
input voltage = 0.15 V,
output voltage = 45 V
(e)
input voltage = 25 mV,
output voltage = 1.5 V
2. In each case below, calculate the output voltage from the
amplifier:
(a) input voltage = 0.15 V,
voltage gain of amplifier = 80
(b)
input voltage = 0.15 V,
voltage gain of amplifier = 200
(c)
input voltage = 18 mV,
voltage gain of amplifier = 30
3. In each case below, calculate the output voltage from the
amplifier:
(a)
voltage gain of amplifier = 250,
output voltage = 90 V
(b)
voltage gain of amplifier = 120,
output voltage = 36 mV
22
Investigation Sheet 1– Increasing the frequency of sound
Aim:
To show how the frequency of sound an air column produces
can be changed
Test tubes of
water
Test tube rack
Instructions
•
•
•
•
•
Set up 5 test tubes in a test tube rack.
Pour a different volume of water in each
Measure the length of the air column in each
Gently blow across the top of each one
Note them down in a suitable table of size of air column and
frequency of sound (value 1 to 5 , 1 being lowest frequency , 5
being highest)
• Explain your results and make some valid conclusions based on
them
Think!
In the test tubes, what is vibrating to give you a sound?
How do you get a lower note or a higher note?
23
Investigation Sheet 2– Reducing Sound Levels
Aim:
To investigate how well sound level can be reduced by
different materials.
Instructions:
speaker
Noise
reduction
Decibel meter
Material
signal
generator
• Set up the apparatus as shown.
• Turn up volume on the signal generator until the decibel meter
reads about 100dB and record this reading.
• Take one of the materials and insert it between the loudspeaker
and the decibel meter.
• Note the new reading on the decibel meter and record it in a
suitable table.
• Remember that the signal generator must not be altered. Be sure
to keep this a fair test.
• Note down how the experiment was kept fair in other ways.
• Repeat the experiment using the different materials provided.
• Display your results on a bar graph.
• Write a report on your experiment include results and
conclusions.
24
Power Point Presentation
You will now work on producing a power point
presentation on one of the following topics:
1. The effects of noise pollution.
2. Mammals with ultrasonic hearing.
3. How are compact discs made?
4. The Mosquito device – teenagers beware!
• You may work on your own or with a partner. Most of the
power point will be completed at home.
• Your power point should contain 8-12 slides.
• It should be informative and well structured containing both
text and pictures.
•
You will present your power point to the rest of the class.
25
Tutorial 2
1.
a) State the noise level for normal conversation at 1m.
________________________________________
b) Give two examples of noise pollution.
________________________________________
c) What level of sound could damage your hearing?
________________________________________
d) How can your ears be protected against very loud noise?
Explain how this works.
_____________________________________________
_____________________________________________
_____________________________________________
_____________________________________________
2.
a) State the range of human hearing. __________________
b) What do we call sounds beyond this range? ____________
c) Give one medical and one non-medical use of these high
frequency sounds.
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
____________________________________________________________
26
3. A public address system is used at airports to give passengers
information. It is made up of three components, as shown below.
Microphone
Amplifier
Loudspeaker
State the function of each of these components
Microphone:__________________________________________
Amplifier:___________________________________________
____________________________________
Loudspeaker_________________________________________
4. Calculate the gain of a guitar amplifier if the input signal is
2.3V and the output signal is 46V.
oscillosco
5. Laura whistles into a microphone connected to an oscilloscope.
The trace produced on the oscilloscope is shown below.
Laura now whistles a louder sound with the same frequency into
the microphone. Which trace shows the new wave pattern
produced on the oscilloscope if the controls are not changed?
Ans:______
27
Unit 1: Section 2 - Additional notes
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
28
____________________________________________
____________________________________________
Unit 1: Section 2 - Additional notes
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
29
____________________________________________
____________________________________________
Unit 1: Section 2 - Additional notes
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
30
____________________________________________
____________________________________________
Unit 1: Section 2 - Additional notes
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
____________________________________________
31
____________________________________________
____________________________________________
32