Lakhmir Singh Manjit Kaur Class 8 Science 13th Chapter “Sound” solution

Lakhmir Singh and Manjit Kaur Science solution: “Sound” Chapter 13. Here you get easy solutions of Lakhmir Singh and Manjit Kaur Science solution Chapter 13 . Here we give Chapter 13 all solution of Class 8. Its help you to complete your homework.

Board – CBSE

Text Book – SCIENCE

Class – 8

Chapter – 13

VERY SHORT ANSWER TYPE QUESTIONS Answers

1) Sound is produced by vibrating objects.

2) Vibrate.

3) An object vibrates to produce sound. A sound making object is different from the one that is silent because it produces vibrations that the silent object does not vibrate.

4) a> Drum produced sound when the stretched membrane of the drum vibrates.

b> Sitar produced sound when a sitar string vibrates.

c> Flute produced musical sounds by the vibrations of air columns inside.

5) Air.

6) 20 mm.

7) a> Woman.

b> Woman.

8) By Human, By Horn, By Heavy construction, By Mikes.

9) Vocal cord.

10) Vocal cord.

11) Sound can travel through solid substance.

12) Thick Thread, water, air.

13) vacuum.

14) Steel

15) water

16) Iron

17) Steel

18) a> gases.

b> solids.

19) 1500 m/s

20) a> Iron, b> Water, c> Air

21) ear

22) Eardrum

23) Hammer, Anvil, stirrup.

24) The Three tiny bones in the middle part of ear as a system of levers and amplify sound vibrations coming from the eardrum before passing them on the inner part of the ear.

25) Auditory nerve.

26) Pinna.

27) Sound.

28) Period is the amount of time T it takes to repeat itself and Frequency is the number of times f it repeats in one time unit. Obviously, f = 1/T. If you measure time in S then frequency is measured in Hz. Frequency is inversely proportional to time period.

29) Frequency, amplitude and Phase are the three characteristics which are used to describe oscillations.

30) Frequency.

31) Amplitude.

32) 125/5= 25 Hz

33) Loudness of the sound produced by a vibrating.  Object depends on the amplitude of vibration. Loudness is proportional to the square of the amplitude.

34) a>  Loudness of a sound will increase double.

b> Loudness of a sound will decrease halved.

35) The unit used to measure the loudness of sound is Decimal.

Symbol is dB.

36) 60 dB

37) Pitch of the sound depends upon its frequency

38) The pitch of a sound you hear depends on the frequency of the sound wave. A high frequency sound wave has a high pitch, and a low frequency sound wave has a low pitch.

39) Woman’s voice have high pitch or woman have a loud voice but man have low pitch voice or men have a low voice than woman.

40) Man’s voice, Women voice, baby’s voice.

41) A whistle.

42) Amplitude- The maximum displacement of a vibrating object from its central position is called the amplitude of vibrations.

Frequency- The number of vibrations made in one second is called the frequency of vibration.

43) Quality (or Timbre).

44) Decibel

45) Ultrasonic sound.

46) Bat produces ultrasonic sound during screaming and we cannot hear ultrasonic sound with the ear. So we cannot hear the screams of a bat.

47) a> 50000 hertz

48)  Air

49) a> True, b> False, c> False, d> False, e> False, f> True, g> false, h> True.

50) a> Vibrating, b> Larynx, c> Vacumn, d> bones, e> Hertz, f>Time-period, g> Frequency, h> Noise, i> Musical, j> Aid.

SHORT ANSWER TYPE QUESTIONS Answers

51) a> Vocal cords.

b> The Vocal cords are stretched across the larynx and they vibrate to produce sound.

52) When we want to speak the muscles of vocal cords contract due to which two vocal cords become stretched and close together leaving only a narrow slit between them. The lungs pass a current of air between the two vocal cords. This air makes the vocal cords vibrate. And the vibrating local cords produce sound.

53) a> High, b> Low

54) The voice of men, women and children are different because of the  they have different length of vocal cords. The vocal cords of a man are about 20 mm long. The vocal cords of a women are about 5 mm shorter than man. Due to the shorter vocal cords the frequency of a woman voice is higher that of a man. Small children have very short vocal cords due to which the frequency of their voice is different.

55) It is more convenient to put the ear to the track if you want to hear a train approaching far away because we can hear the vibrations from the ground when we put our ear at the track.

56) During rainy season, the flash of lighting is seen first and the sound of thunder is heard a little later.

57) This is because the speed of sound in air is about 340 m/s and speed of light in air is 300,000,000 m/s this means that sound travels at a slow speed but light travels much much faster than sound. It is due to very high speed of light that we see the flash of lightning fast and it is due to a comparatively low speed of sound that the thunder is heard a little later.

58) a> strings, b> membrane, c> wooden tube or metal tube, d> vibrations of thick plate, e> string, f> membrane.

59) a> sitar, Veena.  b> flute, trumpet.  c> Tabla, Dholak. d> cymbals, Noot.

60) a> sitar, Veena.  b> flute, trumpet.  c> Tabla, Dholak. d> cymbals, Noot.

61) We can hear following frequencies: a> 6 hertz, b>5000 hertz, c> 10000 hertz, e> 18 KHz.

We cannot hear frequency d> 35000 hertz.

62) a> 20000 hertz,

b> 20 hertz,

c> Bat, Dog.

63) a> A repeated back and forth motion is called Vibration.

The maximum displacement of a vibrating object from a central position is called the amplitude of a vibration.

b> 20 Hz.

64) (a) Two methods are: Vibration of string, vibrations of air column.

(b) With the help of sound waves, sound can travel through air to reach our ears.

65) (a) Sound can’t be heard on the surface of moon because there is no air on the moon to carry the sound waves.

(b) Astronauts talks to each other with the wireless setup using radio waves.

66) (a) Pitch of a sound depends on the frequency of vibration. In fact, the pitch of a sound is directly proportional to its frequency.

Quality is that characteristics of sound that enables us to distinguish between the sounds produced by different sound producing object even they are of same loudness or pitch.

(b) The sounds having too high frequency which can’t be heard by human beings called ultrasound.

The two uses are:-

(i) Ultrasound is used as a diagnostics tool in Medical science to investigate inside of the human body.

(ii) Ultrasound is used to study the growth of foetus.

68) a> To see the membrane of the tabla during hitting with our hand, we can see that the sounding tabla is vibrating.

b>  The loudness of a sound depend on the pitch.

69) This is due to the fact that sound travels much more faster through the railway line made of steel then through air. In fact, sound travels about 15 times faster in steel than in air. So if we want to hair a train approaching far away, it is more convenient to put the ear to the railway track.

70) In vacuum, there is no air molecule, so sound cannot travel through vacuum.

71) a> Noise pollution.

b> We should not put a pin or pencil in our ears because it will damage our ear drums.

72) Two common musical instruments are : Flute and tabla.

In flute, the vibrating parts are air columns.

In table, the vibrating parts are membranes.

73) The difference between music and noise are the sounds which are pleasant to hear are called music but if a musical sound becomes too loud, it would become noise.

Yes, music becomes noise sometimes when very loud music is played at a disco and when a band plays loudly during a marriage procession.

75) a> The two causes of noise pollution from home are :

  • The loud playing of radio, stereo-systems and televisions.
  • Some kitchen appliances.

b>  The usual causes of the partial hearing loss suffered by a person are illness, ear infection, injury or old age.

LONG ANSWER TYPE QUESTIONS Answers:

76) When clapper hits the bell, the bell vibrates. The vibrating bell makes the nearby air molecules to vibrate back and forth. These vibrating air molecules make the next layer of air molecules to vibrate. When these vibrating air molecules fall on our ears, we can hear the sound of ringing bell cannot reach our ears and hence we cannot hear the sound of ringing bell. When there is vacuum in glass jar, there are no air molecules to carry sound vibrations. That’s why sound cannot travel through vacuum.

77) a> The time taken by a vibrating object to complete one vibration is called time-period.

Its unit is called ‘second’

b> The number of vibrations made in one second is called the frequency of vibrations.

Frequency is measured by ‘Hz’.

79) a> When a musical sound becomes too loud, then it would become Noise.

Two examples are :

  • The motor vehicles running on the road produce noise.
  • The bursting of crackers.

b> The sounds which are pleasant to hear are called musical sounds.

Two examples are:

  • The strings of a sitar make regular vibrations to produce musical sounds.
  • Harmonium also produced musical sound.

80) a> The presence of loud, unwanted and disturbing sounds in our environments is called noise pollution.

The source of the noise pollution are surrounding are:

  • The motor vehicles running on the road produce noise.
  • The bursting of crackers.

b> The harmful of noise pollution to human beings are:

  • Loud noise can great harm to human ears. Constant loud noise reduces the hearing power of our ears.
  • Loud noise can cause a person t o lose concentration in work or studies.

c> The various measures to control noise pollution are below:

  • We should not play radio, stereo-systems and television too loudly.
  • The horns of motor vehicles should not be blown unnecessarily.

d> The horns of motor vehicles should not be blown unnecessarily and we should to use big trees to reduce noise pollution.

Thank You


3 Comments

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  1. sir it very good but sst you should post. @arupsarkar@shoutout we want chapter -14

  2. It is very helpful for me
    Thanks for the solutions
    But some questions answered are not given please post this answers

    1. No Please….

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