Class-8-Science Chapter 13 Sound Question and Answer

Question 1: How is sound produced?

Answer: Sound is produced due to the vibration of the object.

Question 2: What should an object do to produce sound?

Answer:The object should vibrate

Question 3: How does a sound making object differ from one that is silent?

Answer: When an object produces sound it actually vibrates. In the case of silent the object is not vibrating and not producing any sound.

Question 4: Name the parts which vibrates to produce sound in the following: (a)Drums, (b)Sitar, (c)Flute

Answer:(a)Skin, (b)Strings, (c)Air holes.

Question5: What brings the sound of a ringing telephone bell to our ears?

Answer: Air brings the sound of a ringing telephone bell to our ears.

Question6: What is the length of vocal cords in a man?

Answer: The vocal cords of a man are about 20 mm long.

Question7: Out of a man or a woman:(a) who has shorter vocal cords?, (b) who produces sound of higer pitch?

Answer: (a) Women have 5mm shorter vocal cord then men.
(b) Women produces sound of higher pitch, and men produce sound of less pitch.

Question8: Give any three sources of sound in a market place.

Answer: Vehicel, Seller, Buyer

Question9: Which part of our body vibrates when we speak?

Answer: Our vocal cord move and vibrates when we speak.

Question 10: Name the sound producing organ in human.

Answer: Larynx

Question 11: What does the working of a toy telephone tell us about sound?

Answer: Sound requires material medium to propogate

Question 12: Name one solid, one liquid and one gas through which sound can travel.

Answer: Iron, Sea water, Dry air

Question 13: Which of the following cannot transmit sound?
Water, Vacuum, Aluminium, Oxygen gas

Answer: Vacuum

Question 14: Is the speed of sound travels faster: air or iron?

Answer: Iron

Question15: In which medium sound travels faster:- air, water or steel.

Answer: Steel

Question16: Out of solid, liquid and gas:-
(a) in which medium sound travels slowest?
(b) in which medium sound travels fastest?

Answer: (a) Gas, (b) Solid

Question17: What is the speed of sound in air?

Answer: 332 m/s

Question18: Name that part of the ear which vibrates when outside sound falls on it.

Answer: Eardrum

Question19: Name the three tiny bones present in the middle part of the ear.

Answer: The malleus, incus, and stapes

Question20: What is the function of three tiny bones in the ear?

Answer: Help in transmitting the sound into the ear

Question 21: Name the nerve which carries electrical impulses from the cochlea of the ear to the brain.

Answer: Auditory nerve

Question 22: What is the name of passage in the outer ear which carries sound waves to the eardrum?

Answer: Sound waves are carried through the ear canal to the eardrum.

Question 23: Name the quantity whose unit is ‘hertz’.

Answer: frequency

Question 24: What is the relation between ‘time-period’ and ‘frequency’ of an oscillating body?

Answer: The time period is the reciprocal of the frequency.
Time period = 1/frequency.

Question 25: Name three characteristics which are used to describe oscillations (or vibrations).

Answer: Frequency, amplitude and Phase

Question 26: What is the scientific name for the following?
The number of vibrations made per second

Answer: Frequency

Question 27: What name is given to the maximum displacement of a vibrating body from its central position?

Answer: Amplitude the maximum displacement of a vibrating body from its central position.

Question 28: If 125 oscillations are produced in 5 seconds, what is the frequency in hertz?

Answer:
No. of oscillations = 125
Total time taken= 5 second
Frequency= 125/5 Hz
= 25Hz

Question 29: How does loudness depend on the amplitude of vibrations?

Answer: Loudness of sound is proportional to the square of the amplitude of the vibration producing the sound. For example, if the amplitude becomes twice, the loudness increases by the factor of 4.

Question 30: By how much will the loudness of a sound change when the amplitude of vibrations is:(a) doubled?, (b) halved?

Answer: (a) doubled, (b) halved.

Question 31: Name the unit used to measure the loudness of sound. Also, write its symbol.

Answer: Decibel(db)

Question 32: What is the loudness of a normal conversation in decibels?

Answer: 60 - 70 Db

Question 33: On what factor does the pitch of a sound depend?

Answer: Frequency is an important factor which maintains the pitch of the sound.

Question 34: How is pitch related to frequency?

Answer: If the pitch is high, the frequency will be high and vice versa.

Question 35: Name the characteristic of sound which enables us to distinguish between a man’s voice and a woman’s voice even without seeing them.

Answer: Pitch

Question 36: Arrange the following sounds in the order of increasing frequencies (keeping the sound of lowest frequency first) : (i) Baby’s voice, (ii) Man’s voice, (iii) Woman’s voice

Answer: ii, iii, i

Question 37: Which produces the sound of a higher pitch: a drum or a whistle?

Answer: Drum

Question 38: Name the characteristic of sound which depends on: (a) Amplitude, (b) Frequency.

Answer: (a) When the amplitude of vibration is large, the sound produced is large and vise versa.
(b) If the frequency of vibration is higher we say that the sound is shrill and has a higher pitch.

Question 39: Name the characteristic of sound which can distinguish between the ‘notes’ (musical sounds) played on a flute and a sitar (both the notes having the same pitch and loudness).

Answer: Tone

Question 40: Write the full form of dB.

Answer: Decibels

Question 41: What is the name of very high-frequency sounds which cannot be heard by the human ear?

Answer: Ultrasonic wave

Question 42: Why do we not hear the screams of a bat?

Answer: Because bat screams at 20,000Hz.

Question 43: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.

Answer: (a) 50,000 hertz

Question 44:State whether the following statements are true or false:
(a) Sound cannot travel in a vacuum.
(b) The number of oscillations per second of a vibrating object is called its time period.
(c) If the amplitude of vibrations is large, the sound is feeble.
(d) The lower the frequency of vibration, the higher is the pitch.
(e) If the amplitude of vibrations is doubled, the loudness of sound also gets doubled.
(f) When the amplitude of vibrations is halved, the loudness of sound becomes one-fourth.
(g) Unwanted or unpleasant sound is termed as music.
(h) Noise pollution may cause partial hearing impairment.

Answer: (a) True
(b) False
(c) False
(d) False
(e) True
(f) False
(g) False
(h) True

Question 45: Fill in the following blanks with suitable words :
(a) Sounds are produced by …………..objects.
(b) The human voice box is called …………..
(c) Sound cannot travel in ………………..
(d) A set of three tiny…………in the middle part of ear passes on sound vibrations from the eardrum to the liquid in the cochlea. (e) The unit of frequency is ………….
(f) The time taken by an object to complete one oscillation is called…………
(g) The shrillness of a sound is determined by the ………..of vibration.
(h) Unpleasant sound is called……………….
(i) Sound which is pleasing to the ear is called…………….sound.
(j) A person having partial hearing loss can hear properly by wearing a device called hearing ……………on the ear.

Answer:(a) vibrating
(b) larynx
(c) vacuum
(d) bones
(e) Hertz (Hz)
(f) time-period
(g) frequency
(h) noise
(i) musical sound
(j) hearing machine

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