Sound - Class 8 - Science
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Back Questions - Sound | NCERT | Science | Class 8
Choose the correct answer. Sound can travel through
(a) gases only
(b) solids only
(c) liquids only
(d) solids, liquids and gases.
(d) solids, liquids and gases.
Voice of which of the following is likely to have minimum frequency?
(a) Baby girl
(b) Baby boy
(c) A man
(d) A woman
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Sign up nowIn the following statements, tick ‘T’ against those which are true, and ‘F’ against those which are false.
(a) Sound cannot travel in a vacuum. (T/F)
(b) The number of oscillations per second of a vibrating object is called its time period. (T/F)
(c) If the amplitude of vibration is large, sound is feeble. (T/F)
(d) For human ears, the audible range is 20 Hz to 20,000 Hz. (T/F)
(e) The lower the frequency of vibration, the higher is the pitch. (T/F)
(f) Unwanted or unpleasant sound is termed as music. (T/F)
(g) Noise pollution may cause partial hearing impairment. (T/F)
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Sign up nowFill in the blanks with suitable words.
(a) Time taken by an object to complete one oscillation is called __________.
(b) Loudness is determined by the __________ of vibration.
(c) The unit of frequency is __________
(d) Unwanted sound is called __________ .
(e) Shrillness of a sound is determined by the __________ of vibration.
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Sign up nowA pendulum oscillates 40 times in 4 seconds. Find its time period and frequency.
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Sign up nowThe 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?
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Sign up nowIdentify the part which vibrates to produce sound in the following instruments.
(a) Dholak
(b) Sitar
(c) Flute
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Sign up nowWhat is the difference between noise and music? Can music become noise sometimes?
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Sign up nowList sources of noise pollution in your surroundings.
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Sign up nowExplain in what way noise pollution is harmful to human
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Sign up nowYour 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.
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Sign up nowSketch the larynx and explain its function in your own words.
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Sign up nowLightning 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 why?
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Sign up nowExtra Questions - Sound | NCERT | Science | Class 8
"How does a sound-making object differ from one that is silent?"
A sound-making object differs from a silent one primarily in its ability to produce vibrations. These vibrations are what generate sound. In contrast, a silent object does not produce these vibrations, hence it does not create any sound.
Which of the following is not a part of a sound wave?
A) Pitch
B) Timbre
C) Color
D) Loudness
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Sign up nowLong Questions - Sound | NCERT | Science | Class 8
Describe the process by which sound is produced, propagated and received. Include the mechanism of vibrating bodies in producing sound, the role of a medium in carrying sound, and the process through which our ears interpret these sounds.
Sound is produced by a vibrating body such as a musical instrument or the human vocal cords. This vibration creates sound waves that require a medium, such as gas, liquid or solid for propagation. The sound cannot travel in a vacuum. These propagating waves reach our ears, where they cause our eardrums to vibrate. These vibrations are sent to the inner ear and then to the brain for interpretation. The loudness and pitch of the sound are determined by the amplitude and frequency of these vibrations, with larger amplitudes producing louder sounds, and higher frequencies producing a higher pitch.
How the amplitude and frequency of sound waves affect the features of sound such as its loudness and pitch. Provide examples to illustrate.
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Sign up nowNumerical - Sound | NCERT | Science | Class 8
A submarine emits a sonar pulse, which returns from an underwater cliff in 1.02 s. If the speed of sound in salt water is 1531 m/s, how far away is the cliff?
To find the distance to the underwater cliff, we use the fact that the sonar pulse travels to the cliff and then back to the submarine. The total time for this round trip is given as (1.02,s).
The speed of sound in salt water is given as (1531,m/s).
The distance (d) to the cliff can be found using the formula for distance:
$$ d = \frac{v \times t}{2} $$
where (v) is the speed of sound in the medium (in this case, salt water), and (t) is the total time for the round trip. We divide by (2) because the given time includes the time to reach the cliff and the time to return.
Substituting the given values:
$$ d = \frac{1531,m/s \times 1.02,s}{2} = \frac{1561.62,m}{2} = 780.81,m $$
So, the underwater cliff is (780.81) meters away from the submarine.
In a thunderstorm, you see the lightning before you hear the thunder. If the sound of thunder reaches you 3 seconds after the lightning is seen, how far away is the storm (consider the speed of sound to be about 340 m/s)?
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Sign up nowShort Questions - Sound | NCERT | Science | Class 8
Explain how sound is produced by a vibrating body.
Sound is produced by a vibrating body when it sets the surrounding medium (such as air, liquid, or solid) into vibration. This vibration propagates through the medium as longitudinal waves which eventually reach our ears. For example, when a school bell is struck, it starts vibrating and these vibrations travel through the air, producing sound that we hear.
What role does a medium play in the propagation of sound?
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Sign up nowWhy can some animals hear sounds that humans cannot?
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