Sound is a form of energy that produces hearing in our ears. It is produced by vibration and travels as a longitudinal wave through compression and rarefaction regions in a medium. The Bell jar experiment showed that sound cannot travel through a vacuum. Sound waves are characterized by their amplitude, wavelength, frequency and speed. Pitch is determined by frequency of vibration and loudness by amplitude.

1. Sound-1

2. Definition and methods of production
▪ Sound is a form of energy which produces a
sensation of hearing in our ears.
▪ Produced by
Methods of producing sound
Plucking
Scratching
Rubbing
Blowing
Shaking
Vibration
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3. Propagation of Sound
A sound wave is a disturbance
that moves through a medium.
Set neighboring particles into
motion.
They in turn produce similar
motion in others.
The disturbance is carried
forward.
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4. Bell jar experiment
▪ Requirements: Electric bell and an
airtight glass bell jar.
▪ Procedure: Electric bell is suspended
inside the jar.
▪ When you press the switch you will be
able to hear the bell.
▪ Start the vacuum pump, air in the jar is
pumped out gradually, the sound
becomes fainter.
▪ When the air is removed completely
no sound is heard at all.
▪ Result: Sound cannot travel in vacuum.
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5. Sound Waves- Longitudinal waves
Compression is the
region of high pressure
Rarefaction is the
region of low pressure
• Sound waves are
longitudinal waves and
travel through a series of
compression and
rarefaction.
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6. Sound Waves- Longitudinal waves
▪ Compression:Where particles are crowded
together and represented by the peak of the curve.
▪ Rarefaction:Where particles are spread apart and
are represented by the valley.
▪ Peak- Crest;Valley-Trough
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7. Characteristics of sound wave
▪ AMPLITUDE:The magnitude of the maximum
disturbance in the medium on either side of the
mean value.
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8. Wavelength
▪ Wavelength Definition: The distance between
two consecutive compressions or two consecutive
rarefactions.
▪ Representation: λ (Greek letter lambda)
▪ SI Unit: metre (m)
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9. Frequency
▪ Frequency Definition:The number of oscillations
per unit time.
▪ Representation: ν (Greek letter, nu)
▪ SI Unit: hertz (symbol, Hz)
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10. Speed
▪ Definition: The distance which a point on a wave,
such as a compression or a rarefaction, travels per
unit time.
▪ Formula: speed, v = distance / time
▪ v = λ ν, That is, speed = wavelength × frequency
since 1/t = frequency.
▪ SI unit: m/s(meters/second)
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11. Pitch and loudness
Speed of vibration of
the source
Affects frequency
Determines pitch
Force with which an
object is made to vibrate
Affects amplitude
Determines loudness
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1. What is vibration?
A.Vibration means a kind of rapid to and fro motion of an object.The
sound of the human voice is produced due to vibrations in the
vocal cords.
2. How does sound propagate?
A. A wave is a disturbance that moves through a medium when the
particles of the medium set neighbouring particles into motion.
They in turn produce similar motion in others.The particles of the
medium do not move forward themselves, but the disturbance is
carried forward.This is what happens during propagation of
sound in a medium.
3.What is the important conclusion of Bell jar experiment?
A. Bell jar experiment shows that sound cannot travel in a vacuum.

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4.Why are sound waves called as mechanical waves?
A. Sound waves are characterized by the motion of particles in the
medium and are called mechanical waves.
5. Can you hear sound in space?
A. Sound requires a medium to travel. In space there is no medium
only vacuum. Due to this, sound cannot be heard in space.
6.What is compression and rarefaction in terms of pressure?
A. Compression is the region of high pressure and rarefaction is the
region of low pressure.
7. How is sound produced in a violin?
A. The sound of a violin is the result of interactions between its
many parts. Drawing a bow across the strings makes the strings
vibrate.This vibration is transmitted through the bridge
and sound radiate into the surrounding air.

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8. Draw a diagram of a Longitudinal wave and show compression
and rarefaction in it
A.
9.What is a transverse wave?
A. In a transverse wave particles do not oscillate along the line of
wave propagation but oscillate up and down about their mean
position .

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10.What are the three important characteristics of sound waves?
A. Frequency
B. Amplitude
C. Speed
11.What is wavelength? Give its unit and symbol
A.The distance between two consecutive compressions (C) or two
consecutive rarefactions (R) is called the wavelength.The
wavelength is usually represented by λ (Greek letter lambda). Its
SI unit is metre (m).
12.What is frequency?Give its unit and symbol
A.The number of oscillations per unit time is the frequency of the
sound wave. It is usually represented by ν (Greek letter, nu). Its SI
unit is hertz (symbol, Hz).

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13.What is amplitude? Give its unit and symbol
A. The magnitude of the maximum disturbance in the medium on
either side of the mean value is called the amplitude of the
wave. It is usually represented by the letter A. Its unit is
meter(m)
14. Define Compression
A. Compressions are the regions where particles are crowded
together and represented by the upper portion of the curve.
The peak represents the region of maximum compression.
15. Define rarefaction
A. Rarefactions are the regions of low pressure where particles
are spread apart and are represented by the valley, that is, the
lower portion of the curve.

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16. Show the crest and trough of a wave using a diagram
A.
17.What is pitch?
A. The faster the vibration of the source, the higher is the
frequency and the higher is the pitch.Thus, a high pitch sound
corresponds to more number of compressions and
rarefactions passing a fixed point per unit time.

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18.What is loudness of sound?
A. The loudness or softness of a sound is determined basically by
its amplitude.The amplitude of the sound wave depends upon
the force with which an object is made to vibrate.
19.What is intensity of sound?
A. The amount of sound energy passing each second through unit
area is called the intensity of sound.
20. Explain the dependence of the speed of sound with the state of
matter and the temperature?
A. The speed of sound depends on the properties of the medium
through which it travels.The speed of sound decreases when we
go from solid to gaseous state. In any medium as we increase
the temperature the speed of sound increases.

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21.What is the difference between a tone and a note?
A. A sound of single frequency is called a tone.The sound which is
produced due to a mixture of several frequencies is called a note
and is pleasant to listen to.
22. Difference between loudness and intensity?
A.The amount of sound energy passing each second through unit
area is called the intensity of sound. Loudness is a measure of the
response of the ear to the sound. Even when two sounds are of
equal intensity, we may hear one as louder than the other simply
because our ear detects it better.
23.Why there is a lag between lightening and thunder?
A. Sound travels with a speed which is much less than the speed of
light.Thus, sound of a thunder is heard a little later than the flash
of light is seen.

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24.A sound wave has a frequency of 2 kHz and wave length 50 cm.
Calculate its speed?
A. Frequency, ν = 2 kHz = 2000 Hz
Wavelength, λ = 50 cm = 0.50 m
We know that speed, v of the wave
= wavelength*frequency
v = λ ν
= 0.50 m × 2000 Hz = 1000 m/s.
25. Calculate the frequency when wavelength is 20 cm and speed is
500 m/s?
A. ν= v/ λ
=500/0.2
= 2500 Hz= 2.5kHz

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26.A sound wave has a frequency of 3 kHz and wave length 20 cm.
Calculate its speed?
A. Frequency, ν = 3 kHz = 3000 Hz
Wavelength, λ = 20 cm = 0.20 m
We know that speed, v of the wave
= wavelength*frequency
v = λ ν
= 0.20 m × 3000 Hz = 600 m/s.
27. Calculate the frequency when wavelength is 10 cm and speed is
200 m/s?
A. ν= v/ λ
=200/0.1
= 2000 Hz= 2.0kHz

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28.What is time period?What is its unit and symbol?
A. The time taken by two consecutive compressions or rarefactions to
cross a fixed point is called the time period of the wave. It is
represented by the symbol T. Its SI unit is second (s).
29. Give the wave shape of high and low pitched sound.
A.

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30. Give the relation between wavelength and frequency.
A. We know that v = λ ν
From the above we can see that wavelength is inversely
related to frequency. So we can conclude that as the
wavelength increases frequency decreases and vice versa.