Transcript General

Intermediate 1
Physics
Sound and Music
Questions
and
Answers
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Intermediate 1
Physics
Sound and Music
Sound Waves Q 1 to 8
Speed of Sound Q 9 to 12
Using Sound Q 13 to 17
Amplified Sound Q 18 to 22
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Sound Waves
1.
An orchestra has various sections like string, brass, percussion etc.....
(a) How do all musical instruments
produce sound energy?
All instruments produce sound by vibrations.
(b) Complete the following:
wave which
Sound is a
energy
transfers
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2. Which of the following are the units of
frequency?
A watts
B decibels
C hertz
D volts.
Answer: C
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3. An oscilloscope can display a musical note on the
screen.
Oscilloscope Screen
microphone
(a)
How many waves are seen on the screen?
(b)
Two waves
The frequency of these waves is 50 Hz.
How many waves are produced in one second?
50 waves in one second
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4.
Jane uses a signal generator to increase the pitch of
the note emitted by the speaker.
The signal generator has an amplitude control and a
frequency control as shown.
Frequency control
Amplitude control
(a)
Which control did Jane turn?
She turned the frequency control.
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Jane now connects an oscilloscope to the generator and
adjusts the amplitude and frequency controls.
Oscilloscope trace before
Jane adjusts the controls
Oscilloscope trace after
Jane adjusts the controls
(b) What did Jane do to the loudness of the note emitted?
Explain your answer.
The note is louder as the wave is taller on the screen.
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Oscilloscope trace before
Jane adjusts the controls
Oscilloscope trace after
Jane adjusts the controls
(c) What did she do to the frequency of the note? Explain
your answer.
She has increased the frequency of the note as there
are more waves on the screen.
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5. Jason generates sounds by striking tuning forks.
The first tuning fork he uses is shown below.
256 Hz
He strikes the tuning fork and produces a note of frequency
256 Hz. The second tuning fork he strikes produces a note
one octave higher than the first.
(a) What is the frequency of the second tuning fork?
512 Hz
(b) What would be the frequency of a note one octave
below the original?
128 Hz
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6. Guitar strings are being tested using the setup shown
below.
Guitar string
The string is plucked and a note of 300 Hz is produced.
State two ways that this setup could be changed to
increase the frequency of the note produced.
Make the string tighter by hanging more weights on
the end or make the string shorter by moving the
bridge closer to the fixed end.
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7. A set of identical measuring cylinders are filled with
different volumes of water. A tune can be played by
blowing across the mouth of the cylinders.
A
B
C
(a) Explain why each cylinder produces a different note.
There are different lengths of air column to vibrate
(b) Which cylinder produces the highest frequency.
Explain your answer.
Cylinder C because it has the shortest column of air
to vibrate
(c) List the cylinders in order of increasing frequency.
A, B, C
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8. Two students are investigating how the frequency of sound
produced by a stretched wire alters as the thickness of the
wire is varied. Their results are shown here.
Thickness of
wire (mm)
1
Length of wire
(m)
0.5
Frequency of
sound (Hz)
800
1
1
400
2
0.5
400
3
0.25
530
4
0.5
200
(a) Which factor, other than thickness affects the
results?
The length of the wire
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(b) Construct a new table, with headings and units, to show
three results which the students should use to enable
them to make a conclusion from their investigation.
Thickness of wire
(mm)
Frequency of sound
(Hz)
1
800
2
400
4
200
(c) What conclusion can the students make from their
investigation?
The thinner the wire the higher the note.
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Speed of Sound
9. A block of flats have to be demolished. When the
explosive is detonated, the observers, who are a safe
distance away, hear nothing. They see the flats
collapsing and sometime later hear the sound of the
explosion.
(a) Explain why nothing is heard immediately.
It takes the sound a few seconds to travel the
distance between the flats and the observers.
(b) Give another example of this effect.
You see the lightning before you hear the thunder
during a storm
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10. Two pupils are given the task of measuring the speed
of sound in air. They are given an air horn and a flag.
Describe how they could measure the speed of sound
in air.
You should:
(a) state any extra apparatus they would need
They would need a measuring tape and a stop clock
(b) state the measurements to be taken
Measure out a distance of more than 200m and turn
to see the other pupil. Wave the flag and sound the
horn at exactly the same time. Start the stop clock
when you see the flag wave and stop the clock when
you hear the horn.
(c) state how the speed is calculated.
Calculate the speed of sound from distance/time.
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11. Sound waves pass through a long pipe. When the sound
reaches sound sensor I the timer is switched on.
After the sound has travelled 10 metres the sound
reaches sound sensor 2 and the timer is switched off.
Sound sensor 1
Sound sensor 2
10 m
Source of
sound w aves
0.000
Timer : displays the time taken in seconds.
The final display on the timer, in seconds, is shown below.
0.029
Calculate the speed of the sound
Speed = distance/time = 10/0.029 = 344.8 m/s
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12. A student wants to find the speed of sound in air using the echo
from a wall.
She stands 300 metres away from a large wall as shown.
Wall
Girl
with
drum
300 m
She now hits the drum and at the same time starts a stop
clock. When she hears the echo of the drum she stops the
clock. The reading from the stop clock is 1.8 seconds.
Use these figures to calculate the speed of sound in air.
Speed = distance/time
= 600/1.8
= 333 m/s
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Using Sound
13. Sound can travel through air. Name four other
substances through which sound can travel - include a
solid, a liquid and a gas.
Wood, glass, water and carbon dioxide. (or any
other sensible answers!!)
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14. Two astronauts are working on the surface of the
Moon. They are about 5 metres away from each other.
One astronaut has a sound sensor on the outside of
his spacesuit. The other astronaut hits two metal
hammers together.
(a) Will the sound sensor detect the sound? Explain your
answer.
No, because there is no atmosphere on the moon
and there will be no particles to carry the sound
energy from the hammers to the sensor.
(b) One of the astronauts hits a rock with a hammer.
Will a sound sensor in the nearby spacecraft detect the
sound?
Yes, because the sound will travel through the
ground to the sensor.
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15. In class, a signal generator is adjusted to the
frequency shown.
2
1
3
4
Hz x 10 000
Robert tells the teacher that he can hear the note from
the loudspeaker.
(a)
Why does his teacher tell him that he is mistaken?
It is producing a sound above 20000 Hz which
means that humans cannot hear it.
(b) State a frequency that would probably be heard by
the whole class.
From about 20 Hz up to about 16000 Hz to be sure
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16. A special sound generator is being
tested in a school laboratory.
A detector with a meter is needed
to pick up the sound since the
frequency is beyond the range of
human hearing.
(a) What is the name of this type of
sound?
Sound
Generator
Ultrasound
(b) Which mammal might be able to hear this sound?
Bats, dogs or dolphins
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16. (c) This type of sound has an important medical use.
Describe what it is used for.
It can be used to check on a baby inside the
mother’s womb or it can be used to break up
kidney stones or gall stones
(d) It is not only medical staff who use this type of
sounding equipment.
In what industry might it be used and how is it
put to good use?
Fishermen use it to search for fish (sonar).
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17. This poster appears on the wall
of a hospital waiting room but
part of the poster has been torn
and some words are missing.
(a) What is the missing word
after "sound level in ..... "?
Decibels
source of noise
sound level in
silence
0
whisper
20
normal conversation
60
warning level
heavy traffic
90
120
(b) The source of sound with a level of 120 is also
torn out of the poster. This source is a source of
noise pollution.
Give some possible examples of noise pollution.
Any unwanted sound is noise pollution!
(c) Why does the lower section of the poster
carry a warning?
Sounds over 90 dB can damage your hearing
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Amplified Sound
18. Four oscilloscope traces are shown. The oscilloscope
controls are all at identical settings.
Trace A is the input signal to an amplifier.
A
B
C
D
(a) Which trace shows the output signal of the
same amplifier? Signal D
(b) The input signal has a frequency of 200 Hz.
State the frequency of the output signal.
200 Hz
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19. The science technician is checking the
0 1 .5 V
amplifier used in the school tannoy system.
AC
V
She connects a voltmeter to the input
terminals of the amplifier and obtains the
reading shown.
When she checks the output voltage from the amplifier the
new reading is 30 V.
(a) How will she calculate the voltage gain of the amplifier?
Use the equation voltage gain = voltage out/voltage in
(b)
What is the gain of this amplifier?
voltage gain = voltage out/voltage in
= 30/1.5 = 20
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20. Music albums are available in tape cassette or compact
disc (CD) format. Cassettes are less expensive, yet CDs
are very popular and sell in great numbers.
(a) State two advantages of a CD compared to a tape
cassette.
Any two from easier to store, high quality sound,
no wear and tear of the disc, very little
background noise
(b) A tape cassette can be used to record your own voice
and then played back. However the recording is not
immediately recognisable as your own voice. Why is this?
We are hearing from the vibrations through the
air only. Usually we hear the vibrations through
the bones in our skull as well.
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21. 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
A
B
changed?
Answer: D
C
D
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22. 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: converts sound into an electrical signal.
Amplifier: makes the electrical signal stronger.
Loudspeaker: converts the electrical signal back to sound
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Intermediate 1
Physics
Sound and Music
End of
Questions and
Answers
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