Download Sound Sound is very important for our life. It is the sound that helps

Sound
Sound is very important for our life. It is the sound that helps us to communicate with each other.
Production of sound –
Sound is produced because of vibration of an object. In other words, a vibrating object produces sound.
Example –
 When a table is beaten, it starts vibrating and produces sound.
 When a drum is beaten, it starts vibrating and produces sound.
 When a stretched rubber band is struck, it starts vibrating and produces sound.
Musical instruments produce different types of sound because of vibration. For example; a flute produce sound because of
vibration in its air column, a guitar produces sound because of vibration of its string, a drum produces sound because of
vibration of its diaphragm.
Sound Produced by Human:
A human being produces sound because of vibration of his voice box. The voice box is also known as larynx. Larynx is situated at
the upper end of windpipe. There are two stretched membranes attached in larynx; with a narrow slit between them. When air
passes through those stretched membranes they produce different types of sound with different combinations of stretching.
Sound needs a medium to propagate:
The traveling of sound is called propagation of sound. Sound cannot propagate in the absence of a medium. The place where
there is no air or air is removed, is called vacuum. Sound does not propagate (travels) through vacuum.
Sound travels through solid, liquid and gas.
We usually hear sound which comes to us through air.
Aquatic animals communicate as sound travels through water also.
We hear the sound through ear
The external ear works like a funnel. Due to its unique shape, sound waves are concentrated once they enter through the
external ears. Then the sound waves reach the ear drum or tympanum. The tympanum is like a stretched membrane; which
vibrates when sound waves strike it. From the ear drum, sound waves reach inner ear; through middle ear. From inner ear,
sound waves are sent to the brain via auditory nerve. The brain interprets these signals and we hear the sound.
Amplitude, Time Period and Frequency of a Sound
Sound travels in the form of wave. When a pebble is dropped in pond water, it produces ripples in water. The ripple is called
wave. Sound travels producing similar waves.
Amplitude and frequency are two important characters of sound. Sounds produced by different object are differentiated by
amplitude and frequency of sound.
Amplitude – The distance from normal to peak is called amplitude. Since, sound travels in the form of wave, so sound has
amplitude.
Frequency: The number of vibrations or oscillations per second is called frequency.
Frequency is expressed in hertz.
If an object oscillates or vibrates 40 times in 1 second, then its frequency will be equal to 40 hertz.
Time period - Time required to produce one complete oscillation is called time period.
Loudness and Pitch
Loudness of sound depends on the amplitude of the sound wave. Greater amplitude produces louder sound and smaller
amplitude produces feeble sound.
Loudness of sound is measured in decibel (dB). Loudness of some types of sound is given here in decibel.
Shrillness or pitch
Frequency of a sound determines the shrillness or pitch of the sound. Shrillness or pitch increases with increase in frequency of
sound. Sound with greater frequency is shriller and has higher pitch. Sound with lower frequency is less shrill and of lower pitch.
Examples:
Children and women produce sound of high frequency and their sound is shriller and of higher pitch. On the other hand, an
adult male produces sound of lower frequency and his sound is less shrill and has lower pitch.
A drum produces sound of lower frequency which is less shrill and has lower pitch, while a whistle produces sound of higher
frequency which is shriller and is of higher pitch.
A lion produces a sound of lower frequency which is less shrill and has lower pitch, while a bird produces sound of high
frequency which is shriller and has higher pitch. However, sound of lion is louder than the sound of a bird.
Audible and Inaudible Sound
Sounds with frequency between 20 Hz to 20,000 Hz are called audible sound. The hearing range of human beings is between 20
hertz to 20,000 hertz.
Sound with frequency below 20 hertz and above 20,000 hertz is called sound of inaudible range. Humans cannot hear the sound
of inaudible range.
Many animals, such as dogs, cats, etc. can hear the sound with frequency above 20,000 hertz.
Noise and Music
Sound that appears unpleasant to us is called noise, such as sound of horn, sound near the site of construction work, sound of
aeroplane, etc.
Sound that appears pleasant to our ear is called musical sound, such as sound of musical instrument, song of a good singer, etc.
Noise Pollution
Loud and excessive sound is unbearable to our ears, and is called noise. Unwanted and excessive sound in our environment
creates noise pollution. Sounds of crackers, factories, vehicles, desert coolers, air conditioners, aeroplane, transistors or
television with high volume, loudspeakers, etc. create sound pollution.
Problems due to Noise Pollution:
Noise pollution can create many types of health related problems, such as lack of sleep (insomnia), hypertension, loss of hearing,
anxiety, etc. Sound above 80 dB is very painful to hear.
A person who is exposed to loud sound continuously may get permanent or temporary loss of hearing (impairment of hearing).
Measures to Limit Noise Pollution
Noise pollution can be limited or controlled by controlling the noise coming from source. Noise pollution can be limited by taking
following measures:
 TV or radio should be played at low volume.
 By installing high quality silencer in vehicles.
 Minimum use of vehicle horns.
 Plantation of trees along the road sides and around buildings. Trees absorb sound.
 Awareness campaign to make people aware; about the harmful effects of noise pollution and measures to control noise
pollution.
Sound
NCERT Solution:
Question: 1. Choose the correct answer :
Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases.
Answer:- (d) solids, liquids and gases.
Question: 2. Which of the following voices is likely to have minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
Answer:- (c) A man
Question: 3. In the following statements, tick T against those which are true, and F against those which are false:
(a) Sound cannot travel in vacuum. (T/F)
Answer: T
(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
Answer: F
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
Answer: F
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
Answer: T
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
Answer: F
(f) Unwanted or unpleasant sound is termed as music. (T/F)
Answer: F
(g) Noise pollution may cause partial hearing impairment. (T/F)
Answer: T
Question: 4. Fill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called ....................
Answer: Time period.
(b) Loudness is determined by the .........................of vibration.
Answer: Amplitude
(c) The unit of frequency is..........................
Answer: hertz
(d) Unwanted sound is called ......................... .
Answer: Noise
(e) Shrillness of a sound is determined by the ................. of vibration.
Answer: frequency and amplitude
Question: 5. A pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
Answer:
Since time period is time taken to complete one oscillation,
Question: 6. The sound from a mosquito is produced when it vibrates its wings at an average rate of 500 vibrations per
second. What is the time period of the vibration?
Answer:
Since time period is time taken to complete one oscillation,
Question: 7. Identify the part which vibrates to produce sound in the following instruments:
(a) Dholak
Answer: Diaphragm (stretched membrane)
(b) Sitar
Answer: String
(c) Flute
Answer: Air column
Question: 8. What is the difference between noise and music? Can music become noise sometimes?
Answer:
Unwanted sound that is unpleasant to ear is called noise. A pleasant sound is called music.
Music can become noise at many instances. When someone tries to enjoy very loud music, it can be noise for someone else.
When loud music is played during religious celebrations or marriages, it can be annoying for many people.
Question: 9. List sources of noise pollution in your surroundings.
Answer:
 Running vehicles.
 Use of loudspeaker.
 Use of TV with high volume.

Question: 10. Explain in what way noise pollution is harmful to humans.
Answer: Noise pollution is harmful to humans in many ways. Constant exposure to noise pollution can create many health
related problems; like insomnia, hypertension and may even lead to loss of hearing.
Question: 11. Your parents are going to buy a house. They have been offered one on the roadside and another three lanes
away from the roadside. Which house would you suggest your parents should buy? Explain your answer.
Answer: I will suggest my parent to buy a house which is away from the roadside, because house at roadside would be noisy
because of running vehicles. On the other hand, the house which is three lanes away from the roadside would be quieter.
Question: 12. Sketch larynx and explain its function in your own words.
Answer: Larynx is composed of two stretched membranes; with some gap between them. When air passes through the larynx,
the membranes or vocal cords vibrate and produce sound. That is why larynx is also known as sound box.
Question: 13. Lightning and thunder take place in the sky at the same time and at the same distance from us. Lightning is seen
earlier and thunder is heard later. Can you explain?
Answer: We know that the speed of light much more than the speed of sound. Due to this, light reaches to us faster than sound.
Hence, during lightning we see the streak of light earlier than hearing the sound of thunder.
Solved Questions
Q1. Define the term Vibration?
Ans. To & fro or back & forth motion of an object is called vibration.
Q2. How is sound produced?
Ans. Sound is produced when an object vibrates.
Q3. Name the part which vibrates to produce sound in the following:
(a) Drums (b) Veena (c) Flute (d) Tabla
Ans. (a) Stretched membrane
(b) Stretched string
© Air column
(d) Stretched membrane
Q4. Name the sound producing organ in humans.
Ans. Voice box or Larynx.
Q5. Describe how sound is produced by the human voice box (or larynx)?
Ans. Two vocal cords are stretched across the voice box or larynx in such a way that it leaves a narrow slit between them for the
passage of air. When the lung forces air through the slit, the vocal cords vibrate to produce sound.
Q6. What is the frequency of the sound produced when the vocal cords are:
(a) Tight & thin?
(b) Loose & thick?
Ans. (a) High frequency (high pitch sound).
(b) Low frequency (low pitch sound).
Q7. Why are voices of men, women & children different?
Ans. The lengths of the vocal cords are different in men, women & children; as a result sounds of different frequencies (or
different pitch) are produced.
Q8. Why a sound cannot be heard on the moon?
Ans. Sound needs a medium ( ie. Solid, liquids or gas) for its propagation. Since there is no atmosphere on the moon to carry the
sound waves, therefore sound cannot be heard on moon.
Q9. Out of solids, liquids & gases:
(a) In which medium sound travels slowest?
(b) In which medium sound travels the fastest?
Ans. (a) Gases.
(c) Solids.
Q9. When we put our ear to a railway line, we can hear the sound of an approaching train even when the train is far off but
its sound can not be heard through the air. Why?
Ans. Because the sound of the train travels much faster through solid railway track made up of steel than through air.
Q10. Define the following terms for a vibrating object:
(a) Amplitude
(b) Time-period
(c) Frequency
Ans. (a) Amplitude: The maximum displacement of vibrating object from its mean position is called the amplitude.
(b) Time-period: The time taken by a vibrating object to complete one vibration is called its time-period. Its unit is ‘second’.
© Frequency: The number of vibrations made per second by a vibrating body is called the frequency. It is measured in ‘hertz’
(written in short form as Hz).
Q11. On what factor does the loudness of sound depends?
Ans. The loudness of sound depends on the amplitude of vibrations. Greater the amplitude of vibrations, louder the sound will
be.
Q12. On what factor does the pitch of sound depends?
Ans. The pitch or shrillness of sound depends on the frequency of vibrations. If the frequency of vibration is low, the sound
produced has a low pitch. On the other hand if the frequency of vibration is high, the sound produced has a high pitch.
Q13. Which produces sound of a higher pitch: a drum or a whistle?
Ans. A whistle.
Q14. Name the characteristic of sound which enables us to distinguish between a man’s voice & a women’s voice even
without seeing them.
Ans. Frequency (or pitch).
Q15. What is the name of high frequency sound wave which cannot be heard by the human ear?
Ans. Ultrasonic. (Sound of frequency greater than 20,000 Hz).
Q16. What is the name of low frequency sound wave which cannot be heard by the human ear?
Ans. Infrasonic (Sound of frequency less than 20 Hz).
Q17. What is the range of audible frequencies?
Ans. 20 to 20,000 Hz.
Q18. What is the difference between noise & music?
Ans. The unpleasant sounds around us are called Noise.
The sounds which are pleasant to us are called Music.
Q19. Explain how, noise pollution is harmful to human beings.
Ans. Noise pollution is harmful to human beings in following ways:
(a) It reduces the hearing power of our ears.
(b) It can cause hypertension (high blood pressure)
(c) It can cause irritation & headache.
(d) Loud noise during night-time disturbs our sleep.
Q20. What type of pollution is caused by the working of mixer & grinder in the kitchen?
Ans. Noise Pollution.
Q21. Discuss the importance of sound in our life.
Sound plays an important role in our life; Sound helps us to communicate with one another.Sound is so important because
animals are able to hear events all around them, no matter where their attention is focused or not
Q22. Why the larynx in human body does vibrate while speaking or singing a song?
Ans:There are two vocal cords which are stretched across the voice box or larynx in such a way that it leaves a narrow slit
between them for the passage of air, when the lungs force air through the slit, the vocal cords vibrate producing sound.
Q23. Define:
Reverberation of sound - The persistence of sound due to repeated reflection and its gradual fading away is known as
reverberation of sound.
Echo: Echo is defined as a repetition of sound due to the reflection of original sound by a large and hard obstacle.
Q24. Sound travels through a medium, it cannot travel in vacuum”. Justify the statement.
Sound travels through a medium solid, liquid and gas. It cannot travel through vacuum.Fill a bucket with water and shake a bell
under the water with one hand make sure that the bell should not touch the body of the bucket. Now place your ear gently on
the water surface, you will hear the sound of the ringing bell, thus we can say that sound can travel through water.Take a metal
rod and hold its one end to your ear, ask your friend to tap at the other end of metal rod you will hear the sound of tapping, thus
this proves that sound can travels through solid.
Q25. The sound from a butterfly is produced when it vibrates its wings at an average rate of 400 vibrations per second. What
is the time period of vibration?
Time period =1/frequency of oscillation
= 1/ 400
= 0.0025 seconds
MCQ
1.Loudness of sound is measured on a scale called:
(A) Vernier scale. (B) Decibel scale. (C) Meter scale.
(D) Screw gauge.
2.What is velocity of sound in water?
(A) 1500 m/s.
(B) 330 m/s.
(C) 200 m/s.
(D) 330 m/s.
3.For an echo to be heard, the minimum distance between the source and reflecting surface must be ………
(A) 17 m.
(B) 17 cm.
C) 10 m.
(D) 10 cm.
4.A pendulum vibrates 50 oscillations in 5 seconds. Calculate its frequency?
(A) 10 Hz.
(B) 20 Hz.
(C) 50 Hz.
(D) None.
5.Sound can travel through:
(A) Gases only.
(B) Solids only.
(C) Liquids only.
(D) Solid, liquids and gases.
6.What is velocity of sound in air?
(A) 300 m/s.
(B) 330 m/s.
(C) 280 m/s.
(D) 200 m/s.
7.The number of oscillations per second is called:
(A) Time period.
(B) Amplitude.
(C) Frequency.
(D) None.
8.On what factor does loudness of sound depend?
(A) Pitch.
(B) Frequency.
(C) Time period.
(D) Amplitude.
9.Sound is produced when objects:
(A) Rotate.
(B) Vibrate.
(C) Circulate.
(D) None.
10.Name the section of throat in which the human voice is produced.
(A) Wind pipe.
(B) Larynx.
(C) Vocal cord.
(D) None.
11.The audible range of frequency for human ear is:
(A) Less than 20 Hz.
(B) 20 to 20,000 Hz.
(C) More than 20,000 Hz.
(D) None.
12.Bats and dolphins can produce and hear sounds with a frequency of:
(A) 12,000 Hz.
(B) 1,20,000 Hz.
(C) 1200 Hz.
(D) 120 Hz.
13.Shrillness of a sound is determined by the ……………… of vibration.
(A) Frequency.
(B) Amplitude.
(C) Time period.
(D) Loudness.
14.Vibrating part of the tabla is:
(A) Stretched membrane.
(B) Stretched string.
(C) Air column.
(D) Water column.
15.Frequency is measured in:
(A) Hertz.
(B) Second.
(C) Per second.
(D) (a) & (c).
16.Vibrating part of the sitar is:
(A) Stretched membrane.
(B) Stretched string.
(C) Air column.
(D) Water column.
17.Vibrating part of the flute is:
(A) Stretched membrane.
(B) Stretched string.
(C) Air column.
(D) Water column.
18.Vibrating part of the Jaltarang is:
(A) Stretched membrane.
(B) Stretched string.
(C) Air column.
19.Waves of frequency greater than 20,000 Hz are called:
(A) Panasonic.
(B) Ultrasonic.
(C) Sonic.
(D) None.
20 .In which medium speed of sound is maximum:
(A) Solid.
(B) Liquid.
(C) Air.
(D) Vacuum.
(D) Water column.
21.A small instrument having two prongs is called:
(A) Tuning fork.
(B) Larynx.
(C) (a) & (b).
(D) None.
22.A sensation depending upon frequency is known as:
(A) Loudness.
(B) Pitch.
(C) Noise.
(D) Shrill.
23.Which is not characteristic of sound:
(A) Pitch.
(B) Noise.
(C) Loudness.
(D) Shrill.
24.Reflected sound is called:
(A) Music.
(B) Noise.
(C) Echo.
(D) None.
25.To and fro motion of an object about its mean position is called:
(A) Oscillatory motion.
(B) Linear motion.
(C) Circular motion.
(D) None.
26.The loudness of sound is proportional to the:
(A) Amplitude.
(B) Square of amplitude.
(C) Frequency.
(D) Square of frequency.
27.If the amplitude of sound become twice then loudness increases by factor:
(A) 2.
(B) 4.
(C) 8.
(D) It will not increase.
28.The voice of a woman has a higher …………… and ………….. than that of a man.
(A) Loudness and amplitude.
(B) Loudness and pitch.
(C) Frequency and pitch.
(D) Frequency and amplitude.
29.High pitch sound has …………… frequency.
(A) high
(B) low
(C) negative
(D) None.
30.Sounds of frequencies less than about 20 vibrations per second called:
(A) Audible.
(B) Ultrasonic.
(C) Inaudible.
(D) None.
31.Presence of excessive or unwanted sounds in the environment is called:
(A) Music.
(B) Noise.
(C) Noise pollution.
(D) None.
32.Which of the following voices is likely to have minimum frequency?
(A) Baby girl.
(B) Baby boy.
(C) A man
(D) A woman.
33.The maximum distance through which a vibrating body is displaced from its mean position is called:
(A) Frequency.
(B) Amplitude.
(C) Pitch.
(D) None.
34.In human beings, voice is produced by the vibration of their:
(A) Wind pipe.
(B) Vocal chord.
(C) Larynx.
(D) None.
35.If an object makes 10 oscillations in 1 second, then what is its frequency?
(A) 1 Hz.
(B) 10 Hz.
(C) 5 Hz.
(D) 8 Hz.
36.If an object makes 10 oscillations in 2 seconds, then what is its frequency?
(A) 1 Hz.
(B) 10 Hz.
(C) 5 Hz.
(D) 8 Hz.
37.If an object makes 10 oscillations in 1 second, then what is its time period?
(A) 1 sec.
(B) 0.1 sec.
(C) 0.01 sec.
(D) 10 sec.
38.Time taken by an object to complete one oscillation is called:
(A) Frequency.
(B) Pitch.
(C) Amplitude.
(D) Time period.
39.Vibration below ……………. is called infra sound.
(A) 10 dB.
(B) 0dB.
(C) 90 dB.
(D) None.
Answer the following questions :
Q.1 How does a sound making object differ from one that is silent?
Q.2 How does sound from a sound producing body travel through air to reach our ears?
Q.3 Why are the voices of men, Women and children different?
Q.4 Why a sound cannot be heard on the moon?
Q.5 How do astronauts talk to one another on the surface of moon and Why?
Q.6 If you want to hear a train approaching from far away, why is it more convenient to put the ear to the track?
Q.7 State one observation from everyday life which shows that sound travels much more slowly than light?
Q.8 What is the scientific name for the following? The number of vibrations made per second.
Q.9 Why do we not hear the screams of a bat?
Q.10 Which of the following frequency of sound can be heard by a dog but not by a man? {a} 50,000 hertz {b} 15,000
hertz
Q.11 Explain how, noise pollution {or excessive loud noise} is harmful to human beings.
Q.12 State the various measures which can be taken to control {or reduce} noise pollution in our surroundings.
Q.13 Give two causes of noise pollution from the homes.
Q.14 Sound of different pitch can be produced using a flute. Explain, how?
Q15.How is a sound produced?
Q16.How is sound propagates?
Q17.What is the amplitude of the wave?
Q18.What is the use of reflection of sound?
Q19.On what factor does loudness of sound depend?
Q20.Where will the sound travel faster, in wood or water?
Q21.Define frequency of sound.
Q22.Define the term pitch.
Q23.Define the term echo.
Q24.What is the audible range of human ear?
Q25.What is the full form of SONAR?
Q26.Name the section of throat in which human voice is produced.
Q27.What is ultrasound?
Q28.Write one difference between musical sound and noise.
Q29.Name the two animals that use echo-location to guide them.
Q30.What is ultrasound?
Q31. State one characteristic of ultrasound which makes it useful in the process of echo-location
Q32.In cinema halls and auditoria, the walls, floor and ceilings are covered by sound absorbing materials, why?
Q33.Write the following frequency in their increasing order: (i) Voice of a child, (ii) Voice of a man, (iii) Voice of a
woman.
Q34.A pendulum produces 20 oscillations in 5 second. Calculate its time period?
Q35.Give reason: (i) During a thunderstorm, we first see the lightning and then hear the thunder. (ii) We do not hear
the supersonic jet approaching, but hear a sudden boom after it has passed away
Q36.How is the human voice produced?
Q37.Explain how sound is produced by each of the following types of musical instruments. (i) Wind instruments. (ii)
String instruments. (iii) Percussion instruments.
Q39.How would you describe the sound produced if :
1. A large number of vibrations are produced per second.
2. The amplitude is small. 3. Vibrations are produced at irregular intervals.
Q40.Sound produced by a mosquito is quite different from the roar of a lion. Explain.
Q41.What do you understand by term noise pollution?
Q42. Suggest some ways of minimizing noise pollution.
Q43.Differentiate between loudness and pitch.
Q44. Name the two animals that use echolocation to guide themselves.
Q 45. Why humans cannot hear the sound of the whistle used for dog training?
Q46. Complete the following table:
HUMAN EAR – STRUCTURE
Loudness of sound from various sources