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Intermediate 1
Physics
Sound and Music

Sound Waves

Speed of Sound

Using Sound

Amplified Sound
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Intermediate 1
Physics
Sound and Music
Sound Waves
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Sound Waves
Vibrations
Musical instruments produce sound when
part of the instrument vibrates.
v _ _ _ _ _ _ _
A guitar string vibrates when it is plucked.
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Vibrations
A trumpet blasts out sound when the aair_ _
inside it vibrates
Energy is transferred from the vibrating
object to the listener by sound wwaves
_ _ _ _
which travel through the air. These sound
waves make the air vvibrate.
_ _ _ _ _ _.
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Frequency
Each note or sound has a frequency which is
measured in h _hertz
_ _ _ (Hz).
A tuning f fork
_ _ _ has the frequency
engraved on it.
This vibrating fork will produce 256
vibrations every s _second.
_ _ _ _.
This means that 256 sound w _waves
_ _ _ are
produced in one second.
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Frequency
F _ Frequency
_ _ _ _ _ _ _
= number of waves produced in one second.
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Frequency
A whistle produces a hhigher
_ _ _ _ _
frequency sound than a vibrating drum.
The whistle has a much higher pitch
p _ _ _ _.
The higher the pitch means the
higher the frequency
f _ _ _ _ _ _ _ _
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Detecting Sound
S _ _Sound
_ _ can be taken in by a
microphone and a trace displayed on an
oscilloscope.
tuning
fork
microphone
Oscilloscope
sound w aves travel from fork to microphone
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Loud and quiet
A loud sound transfers more e _energy
_ _ _ _ so
the oscilloscope trace will have a llarge
_ _ _ _
amplitude. The amplitude of a wave is the
distance from the m _ middle
_ _ _ _ of the wave
to the top or bottom of the wave.
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Loud and quiet
Loud note
has large
amplitude
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Loud and quiet
A soft/quiet sound transfers less
l _ _ _
energy so the oscilloscope trace will have
a s _ small
_ _ _ amplitude
Quiet note
has small
amplitude
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High and Low Frequency
The effect of changing the frequency of a
note can be seen on the oscilloscope screen.
Sound A
has low
frequency
Sound
sound
Sound B
has high
frequency
B_ has a higher frequency than
_
A .
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High and Low Frequency
If the frequency is doubled, we say that
sound B is an o _ octave
_ _ _ _ higher than
sound A.
frequency:
(Hz)
256
512
1024
one octave
t _two
_ octaves
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Changing the Note
A musician tunes a guitar by making the
string t _ tighter
_ _ _ _ _ or looser.
While playing the guitar, the note is
changed by altering the llength
_ _ _ _ _
of string which vibrates.
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Changing the Note
S _Short
_ _ _ strings
produce a higher frequency
than long strings.

T _Tight
_ _ _ strings
produce a higher frequency
than slack strings.

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Changing the Note
An organ produces a variety of musical
notes which depend on the llength
_ _ _ _ _
of the air column which vibrates. The
shorter pipes have the shorter air columns
which produce the hhigher
_ _ _ _ _
frequency notes.
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Intermediate 1
Physics
Sound and Music
Speed
of
Sound
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Speed of Sound
During a thunderstorm, the lightning flash is
seen a short time b _between
_ _ _ _ the roll
of thunder is heard. This is due to the fact
that l _light
_ _ _ travels much faster than
sound through the air.
In air:
Speed of light = 300 000 000 m/s
Speed of sound = 340 m/s
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Calculating the Speed of Sound
In a laboratory the speed of sound can
be calculated using the formula below.
distance
speed =
time
(meaning; speed equals distance
d _ _ _ divided
_ _ _ by time)
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Speed of Sound : Apparatus
electronic timer
Hammer
different
microphone A
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microphone B
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Speed of Sound
A loud sound is made. As the sound reaches
microphone A, the timer starts
s _ _ _ _ _.
When the sound waves reach microphone B,
the timer s _stops
_ _ _ . The distance
between the microphones is measured with a
m _
_ _ _ stick.
metre
The experiment can be rrepeated
_ _ _ _ _ _ _
to calculate a more accurate, average result.
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Speed of Sound
Example:
Recorded times: 0.0030 s, 0.0029 s, 0.0031 s,
0.0027 s, 0.0029 s
Average time = 0.0146/5 = 0.0029 s
Distance travelled = 1 metre
Speed
= distance/time
= 1.0/0.0029
= 344.8 m/s
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Intermediate 1
Physics
Sound and Music
Using Sound
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Using Sound
Sound can travel through ssolids,
_ _ _ _ _,
liquids and gases.
g _ _ _ _.
The only thing that sound cannot pass
through is a vacuum.
v _ _ _ _ _.
A vacuum is an e _empty
_ _ _ space, so
there are no particles to pass on the
vibrations.
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Using Sound
When listening to music, you hear
s _sounds
_ _ _ _ with a wide range of
frequencies. We can detect sounds
that range from about 20 hertz to
20 000 hertz. As we get oolder
_ _ _ _,
the upper limit gradually falls to about
15 000 hertz.
Some animals can detect higher
frequency sounds than humans.
h _ _ _ _ _.
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Using Sound - Ultrasound
Sound beyond the u _upper
_ _ _ limit of human
hearing (20 000 Hz) is called ultrasound.
Ultrasound can be used in hospitals to scan
the b baby
_ _ _ in the mother's womb.
This can be used by a computer to produce an
i _image
_ _ _ of the baby on a screen.
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Using Sound - Ultrasound
A system called s _sonar
_ _ _ is used
by fisherman at sea.
The ultrasound signal is transmitted
towards the sea bed and an e echo
_ _ _
is detected.
Shoals of f _
_ _ are located by
fish
this method.
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Sound Levels
The sound level of a noise means
how l_loud
_ _ it is.
The sound level varies depending on
the source of the sound.
Sound level is measured in
d _ _decibels
_ _ _ _ _ (dB).
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Sound Levels
130 J Jet
_ _ engine at 50 metres
100 Pneumatic drill
d _ _ _ _
Sound
l level
____
(dB)
70 Rush hour ttraffic
_ _ _ _ _ _
0
S _ _ _ _ _ _
Silence
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Sound Levels
When sound levels rise to unacceptable levels, the
problem is described as n _noise
_ _ _ pollution.
There are many sources of noise pollution, such as
aircraft noise or pneumatic drills. Exposure to high
sound levels over a long time can ddamage
_ _ _ _ _
our hearing. Listening through stereo headphones will
produce a harmful effect if the v _ volume
_ _ _ _ is
turned to maximum.
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Intermediate 1
Physics
Sound and Music
Amplified
Sound
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Amplified Sound
A stereo system can be used to l _ listen
_ _ _ _ to
a compact disc (CD) or a radio programme. No
matter what function is selected, the signal passes
through an amplifier which turns a small amplitude
electrical s _ signal
_ _ _ _ into a higher amplitude
one.
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Amplified Sound
Amplifier
large amplitude output signal
small amplitude input signal
Only the amplitude of the signal is changed. The
frequency does n not
_ _ change.
When announcements are made at airports and stations,
the message has to be changed from sound into
e _ _ _electrical
_ _ _ _ _ _ signals and back to sound.
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Amplified Sound
When announcements are made at airports and stations,
the message has to be changed from sound into
e _ _ _electrical
_ _ _ _ _ _ signals and back to sound.
An electronic system of 3 parts is used to amplify the
s _
_ _ _ given out by the announcer
signal
sound
Input
microphone
Process
amplifier
Output
loudspeaker
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sound w ith
increased
amplitude
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Amplified Sound
Part of the system
Function
m _ _ microphone
_ _ _ _ _ _ _
converts sound into an
e _ _ _electrical
_ _ _ _ _ _
signal
a _ _ _amplifier
_ _ _ _ _
makes the electrical signal
sstronger
_ _ _ _ _ _ _
(bigger amplitude)
converts the electrical
l _ _ _loudspeaker
_ _ _ _ _ _ _ signal back to ssound
_ _ _ _
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Voltage Gain
The performances of different amplifiers
can be compared by finding the gain of the
amplifier.
Voltage gain =
0utput voltage
Input voltage
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Voltage Gain
Example:
Find the voltage gain of the following amplifier.
input
0.01V
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output
4V
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Voltage Gain
Voltage gain =
0utput voltage
Input voltage
=
4
0.01
=
400
N.B. Voltage gain is just a number.
It has no unit
u _ _ _.
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Playback
A recording of your own v _voice
_ _ _ will sound a
bit strange when it is played back from a cassette.
This is because we normally hear our own voice by:
vibrations of bones in our s _skull
_ _ _ and
ears
vibrations in the air being detected by our e
_ _ _
When we listen to a recording of our own voice we
hear it by:
vibrations in the aair_ _ being detected by our
ears only.
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Playback
A CD (compact disc) is a source of high
h _ _ _
quality sound. As the CD spins inside the CD
player, light from a l _laser
_ _ _ reflects off the
CD. There is no wear and tear of the disc surface
and there is very little background noise.
n _ _ _ _.
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Intermediate 1
Physics
Sound and Music
End of Unit
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