(a) Natural vibrations

(b) Damped vibrations

(c) Forced vibration

(d) Resonant vibrations

Ans: When a body vibrates under a periodic force, the vibrations of the body are
forced vibrations. Hence the correct answer is option c.

65. A tuning fork of frequency 256 Hz will resonate with another tuning fork of
frequency.

(a) 128 Hz

(b) 256 Hz

(c) 384 Hz

(d) 512 Hz

Ans: A tuning fork of frequency 256 Hz will resonate with another tuning fork of
frequency 256 Hz. Hence the correct answer is option b.

66. Name three characteristics of a musical sound.

Ans: The three characteristics of sound are as follows:

(a) Loudness

(b) Pitch or shrillness

(c) Quality or timber

Class X Science www.vedantu.com 29

67. (a) Which of the following quantities determines the loudness of a sound
wave?

(i) Wavelength

(ii) Frequency

(iii) Amplitude

Ans: The amplitude of the wave determines the loudness of a sound wave. Larger
amplitude means a loud sound while smaller amplitude means a soft sound. Hence
amplitude is the answer.

(b) How is loudness related to the quantity mentioned in above part (a)

Ans: The loudness is proportional to the square of the amplitude.

68. If the amplitude of a wave is doubled, what will be the effect on its loudness?

Ans: Since the loudness of sound is directly proportional to the square of amplitude.
Therefore if the amplitude of the wave is doubled then the sound will become four
times louder.

69. Two waves of the same pitch have amplitudes in the ratio 1.3. What will be
the ratio of their,

(i) Loudness

Ans: Loudness is proportional to square of amplitude. Therefore the ratio of

loudness = 1. 9

(ii) Frequencies

Ans: If pitch is unchanged, then the frequency remains the same. Therefore the ratio
of frequencies = 1. 1

Class X Science www.vedantu.com 30

70. How does the wave pattern of a loud note differ from the soft note? Draw a
diagram.

Ans:

71. Name the unit in which the loudness of sound is measured?

Class X Science www.vedantu.com 31

Ans: The loudness of the sound is measured in units called decibels.

72. Why is the loudness of the sound heard by a plucked wire increased when it
is mounted on a soundboard?

Ans: The loudness of the sound heard by a plucked wire increases when it is
mounted on a soundboard. This is because the board provides almost a large area
and forces a large volume of air to vibrate and therefore increases the sound energy
reaching our ears.

73. Define the term intensity of a sound wave. State the unit in which it is
measured.

Ans: The intensity of the sound wave at a point of the medium is defined as the
amount of sound energy passing per second normally through an unit area at that
point. The unit of the intensity of the sound wave is watt per meter2 (Wm - 2).

74. How is the loudness of sound related to the intensity of the wave producing
it?

Ans: The relationship between loudness L and the intensity I is as follows.

L = K log10I [where K is constant of proportionality].

75. Comment on the statement 'loudness of sound is a subjective nature, while

intensity is an objective nature'

Ans: The intensity of a sound wave at a point of the medium is the amount of sound
energy passing per second normally through the unit area at that point.The loudness
of a sound depends on the intensity which means that the energy conveyed by the
sound wave near the eardrum of the listener. The loudness also depends on the

Class X Science www.vedantu.com 32

sensitivity of the ears of the listener. Therefore the loudness of the sound of a given
intensity may differ from listener to listener. The two sounds of the same intensity
but of different frequencies may differ in the loudness even to the same listener. This
is due to the sensitivity of the ears to different frequencies. Hence loudness has a
subjective nature while intensity, being a measurable quantity, has an objective
nature.

76. State three factors which affect the loudness of sound heard by a listener.

Ans: The loudness of the sound heard by a listener depends on the factors mention
as follows.

(a) The loudness is proportional to the square of the amplitude

(b) The loudness is inversely proportional to the square of distance

(c) The loudness depends on the surface area of the vibrating body.

76. The bells of a temple are big in size. Why?

Ans: According to the study of bells the larger bells provide less resonant frequency.
It is essential that the frequency of the sound is less for a sound wave to travel long
distances. Also it is observed that thicker the body of a bell, the quality of sound will
be richer. Therefore the bells of a temple are big in size.

77. Name the unit used to measure the sound level.

Ans: The unit to measure the sound level is called the decibel.

78. What is the safe limit of sound level in dB for our ears?

Ans: The safe limit of the sound level in dB for our ears is up to 120 dB.

Class X Science www.vedantu.com 33

79. What is meant by noise pollution? Name one source of sound causing noise
pollution.

Ans: The disturbance produced due to undesirable loud and harsh sound of level
above 120 dB from the various sources such as the loudspeaker, moving vehicles etc
in the environment is the noise pollution.

80. What determines the pitch of sound?

Ans: The pitch of a note depends on its frequency. Two notes with same amplitude
sounded on the same instrument, will differ in pitch when their vibrations are of
different frequencies.

81. Name the subjective property of sound related to its frequency.

Ans: The pitch is the subjective property of the sound related to its frequency.

82. Name and define the characteristic which enables one to distinguish two
sounds of same loudness, but of different frequencies given by the same
instrument.

Ans: The characteristic by which two sounds of same loudness, but of different
frequencies given by the same instrument can be distinguished is called the pitch.

83. Draw a diagram to show the wave pattern of a high pitch note and a low
pitch note, but of the same loudness.

Ans: The diagram for high pitch notes is as follows.

Class X Science www.vedantu.com 34

The diagram for low pitch notes is as follows.

Class X Science www.vedantu.com 35

84. How is it possible to detect the filling of a bottle under a water tap by hearing
the sound at a distance?

Ans: The length of the air column decreases with rise in the water level in a bottle
kept under a water tap. Therefore the frequency of sound produced increases. Thus
one can get the idea of water level in the bottle by hearing sound from a distance.

85. The frequencies of notes given by flute, guitar and trumpet are respectively
400 Hz, 200 Hz and 500 Hz. Which one of these has the highest pitch?

Ans: Given that the frequencies of notes by flute, guitar and trumpet are respectively
400 Hz, 200 Hz and 500 Hz. From the given frequencies the frequency of the trumpet
is highest. Hence the trumpet has the highest pitch.

86. Complete the following sentences.

(a) The pitch of sound increases, if its frequency ___________.

Ans: The pitch of sound increases, if its frequency increases.

(b) If the amplitude of the sound is halved, its intensity becomes __________.

Ans: If the amplitude of the sound is halved, its intensity becomes one-fourth.

87. The diagram below shows three different modes of vibration P, Q and R of
the same string of a given length.

Class X Science www.vedantu.com 36

(a) Which vibration will produce a louder sound and why?

Ans: The amplitude of R is maximum. Therefore R will produce a louder sound.

(b) Which vibration will produce a sound of maximum shrillness (or pitch) and
why?

Ans: The frequency of P is maximum. Therefore P will produce a maximum

shrillness.

(c) What is the ratio of wavelength of vibrations P and R?

Ans: The ratio of wavelength of vibrations P and R is [λp: λR = 1 : 3].

88. Name the characteristic which enables one to distinguish the sound of two
musical instruments even if they are of the same pitch and same loudness.

Ans: The quality or timber of sound is the characteristic which enables one to
distinguish the sound of two musical instruments even if they are of the same pitch
and same loudness.

Class X Science www.vedantu.com 37

89. How do the two sounds of same loudness and same pitch produced by
different instruments differ? Draw diagrams to illustrate your answer.

Ans: The two sounds having the same loudness and same pitch produced by the
different instruments differ due to their different waveforms. The waveforms depend
on the number of the subsidiary notes and their relative amplitude along with the
principal note. The below diagram shows the wave patterns of the two sounds having
same loudness and same frequency but have different waveforms. One is a sine wave
and the other is a triangular wave.

90. Two identical guitars are played by two persons to give notes of the same
loudness and pitch. Will they differ in quality? Give a reason for your answer.

Ans: Since the guitars are identical, they will have a similar waveform and thus will
have the similar quality.

Class X Science www.vedantu.com 38

91. Two musical notes of the same pitch and same loudness are played on two
different instruments. Their wave patterns are as shown in the diagram below.
Explain why the wave patterns are different.

Ans: The different instruments produce different subsidiary notes. A note played on
one instrument has a large number of the subsidiary notes, while the same note
played on another instrument contains only a few subsidiary notes. Therefore they
have different waveforms.

92. Which characteristic of sound makes it possible to recognize a person by his

voice without seeing him?

Ans: The quality or timbre of sound is the characteristic which enables us to

recognize a person by his voice even if we can’t see him.

93. State the factor that determines

(i) The pitch of a note

Class X Science www.vedantu.com 39

Ans: The frequency determines the pitch of a note.

(ii) The loudness of the sound heard

Ans: The amplitude determines the loudness of the sound heard.

(iii) The quality of the note.

Ans: The waveform determines the quality of the note.

94. Name the characteristic of the sound affected due to a large in its

(i) Amplitude

Ans: The characteristic of the sound affected because of the large amplitude present
in it is loudness.

(ii) Wave form

Ans: The characteristic of the sound affected because of the large waveform present
in it is quality.

(iii) Frequency

Ans: The characteristic of the sound affected because of the large frequency present
in it is pitch.

95. The sketches I to IV in figure show sound waves, all formed in the same time
interval.

Class X Science www.vedantu.com 40

Which diagram shows;

(i) A note from a musical instrument

Ans: A figure IV is a note from a musical instrument.

(ii) A soft (or feeble) note

Ans: A figure I is a soft (or feeble) note.

(iii) A bass (or low frequency) note.

Ans: A figure II is a bass (or low frequency) note.

96. Shows the wave patterns of three sounds A, B and C.

Class X Science www.vedantu.com 41

Name the characteristic of sound which is same between,

(i) A and B

Ans: Both A and B have the same amplitude and waveform. Therefore loudness and
quality are the same.

(ii) B and C

Ans: In figures B and C, neither amplitude nor waveform is same. Hence no

characteristic is the same.

(iii) C and A

Ans: In figures C and A, frequency of both the sound is same and therefore the pitch
is same.

97. A microphone is connected to the Y-input of a C.R.O. Three different

sounds are made in turn in front of the microphone. Their traces (a), (b) and
(c) produced on the screen are shown in figure.

Class X Science www.vedantu.com 42

(i) Which trace is due to the loudest sound? Give reason for your answer.

Ans: Figure (b) is due to the loudest sound because amplitude is largest

(ii) Which trace is due to the sound with the lowest pitch? Explain your answer.

Ans: Figure (a) is due to the sound with the lowest pitch because frequency is lowest

98. In what respect does the wave pattern of a noise and music differ? Draw a
diagram to explain your answer.

Ans:

Class X Science www.vedantu.com 43

The above figure shows the waveforms of a music and a noise.The wave pattern is
regular in music while the wave pattern of a noise is irregular.

99. State one difference between a musical note and a noise.

Ans: The difference between a musical note and a noise are:

Noise Musical note

This is harsh, discordant and This is regular, smooth and
1 1
unpleasant to the ear. pleasant to the ear.
The sound level is high, that is above The sound level is low, between
2 2
120 dB. 10 dB to 30 dB.

100. By reducing the amplitude of the sound wave, its.

(a) Pitch increases

(b) Loudness decreases

Class X Science www.vedantu.com 44

(c) Loudness increases

(d) Pitch decreases

Ans: If the amplitude of the sound wave is reduced, its loudness decreases. Hence
the correct answer is option b.

101. Two sounds of same loudness and same pitch produced by the two different
instruments differ in their

(a) Amplitudes

(b) Frequencies

(c) Wave forms

(d) All the above

Ans: The two sounds of same loudness and same pitch produced by the two different
instruments differ in their waveforms. Hence the correct answer is option c.

102. Two sounds A and B are of same amplitudes, same wave forms but of
frequencies f and 2f respectively. Then.

(a) B differ in quality from A

(b) B is grave, A is shrill

(c) B is shrill, A is grave

(d) B is louder than A

Ans: Two sounds A and B are of same amplitudes, same wave forms but of
frequencies f and 2f respectively. Then B is shrill, A is grave. Hence the correct
answer is option c.

Class X Science www.vedantu.com 45