Sound-NCERT Solutions

Class VIII Science
NCERT Solution for Sound
Q.1.   Choose t.e correct answer. Sound can travel through:
           (a) gases only
(b) solids only
           (c) liquids only
(d) solids, liquids and gases.
Ans. (d) solids, liquids and gases.
Q.2.   Voice of which of following is likely to have minimum frequency?
           (a) Baby girl
(b) By boy
           (c) A man
(d) A woman..
Ans. (a) Baby girl.
Q.3.   In the following statements, tick 'T� again t hose which arse tare, ara ‘F’ against the which are false:
           (a) Sound cannot trarl in vacuum.
           (b) The number of oscillations per second of a vibrating objet is called its time period.
           (c) If the amplitude of vibration is large, sound is feeble.
           (d) For human ears, the audible range is 20 Hz to 20,000 .
           (e) The lower the frequency of vibration, the higher is the pitch.
           (f) Unwanted or unpleasant sound termed as music.
           (g) Noise pollution may cause partial hearing impairrraent.
Ans. (a) True (b) False (c) False
           (e) False (f) False (g) True.
Q.4.   Fill in the blanks ith suitable words:
           (a) Time taken by an object to a complete one oscillation is called__________.
           (b) Loudness as determined the ___________of uibration.
           (c) unit of fqueracy is __________.
           (d) Unwanted sound is called __________.
           (e) Shrillness of a sound is determined by the __________ of vibration.
Ans. (a) time period (b) amplitude (c) hertz (d) noise
           (e) frequency
Q.5.   A pendulum oscillates 40 times is 4 seconds. Find its time period and frequency.
Ans. Number of oscillations = 40
           Total time = 4 seconds
Q.6.   The sound from a mosquito i produced when it vibrates its wings at an average rate of 500 vibrations per seconds, what is the time period of the vibrations?
Ans. Total vibrations = 500
           Time taken = 1 second
           So time period = 0.002 seconds.
Q.7.   Identify the part which vibrates to produce sound in following instruments.
           (a) Dholak
(b) Sitar
(c) Flute.
Ans. (a) Stretched membrane
(b) Strings
(c) Air column.
Q.8.   What is the difference between noise and music? Can music become noise sometimes?
Ans. The sound which is unpleasant for our ears is called noise while music is the sound which is pleasant for our ears. Music becomes noise sometimes when it crosses the bearable range of sound for our ears.
Q.9.   List sources of noise pollution in your surroundings.
Ans. Sources of noise pollution: Honking of horns, loud speakers, loud sounds of machines in factories, loud sounds of T.V., radio, domestic appliances etc.
Q.10.   Explain in what way noise pollution is harmful to humans?
Ans. Harmful effects of noise pollution:
           (i) It causes deafness.
           (ii) It causes mental illness.
           (iii) It causes headache and high blood pressure.
Q.11.   Your parents are going to buy a house. They awe been offered one on the road side and another three ides away from the road side. Which house would you suggest your parents to buy? Explain your answer.
Ans. I would suggest my parents to buy house three lanes away from the roadside. This house would safeguard our health and peace of mind.
Q.12.   Sketch larynx and explain its function in your own words.
Ans. Larynx is also known as voice box. It has vocal cords which have air column vibrating in them, which cause sound in humans
Q.13.   Lightening an 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?
Ans. The speed of light is more than that of sound. Due to more speed the light reaches us before the sound does. So lightening is seen earlier and thunder is heard later.