CBSE Physics help class 8 Chapter: Sound
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1. What is the
difference between noise and music?
Answer: Unpleasant sounds are
called noise whereas music is a sound, which produces pleasant sensation. But,
if the musical sound is too loud, it becomes noise.
2. What is
eardrum? How does it play an important role in hearing?
Answer: A thin tightly
stretched membrane t is called eardrum. it vibrates sound wave and sends
vibrations to the inner ear.
3. Which property of vibrations determines the pitch of the sound? Explain giving some examples.
Answer: The frequency determines the shrillness or pitch of a sound. If the frequency of vibration is higher the sound has a higher pitch. If the frequency of vibration is lower, the sound has a lower pitch. Women sound is shriller than man due to high frequencies
4. What is the audible range of frequencies for human beings?
Answer: The range of audible frequencies is roughly between 20 to 20,000 Hz.
Dogs can hear frequencies up to 40,000 Hz while cats can produce and hear frequencies up to 70,000 Hz.
5. What is noise pollution? What are its major causes?
Answer: Presence of excessive or unwanted sounds due to irregular frequencies in the atmosphere is called noise pollution.
Major causes of noise pollution are sounds of vehicles, explosions including bursting of crackers, machines,
loudspeakers etc.
6. How can the noise pollution be controlled in a residential area?
Answer: Noise producing industries should be set up away of such areas. Use of automobile horns be minimized. TV and music systems should be run at lower volumes. Plants must be planted along the roads and around buildings to minimize the harmful effects of noise pollution.
7. What are the harms of noise pollution?
Lack of sleep, high blood pressure, anxiety and many more health disorders are caused by noise pollution. if a person is exposed to a loud sound continuously may get temporary or even permanent deafness.
8. How does the loudness of sound depend upon the amplitude?
Loudness of sound is proportional to the square of the amplitude of vibration producing the sound. For example, if the amplitude becomes twice the loudness increases 4 times.
9. Why a tabla with tight membrane does vibrates at a higher pitch than a tabla with a loose membrane?
Answer: A tight membrane vibrates at a much higher frequency than a loose one, so that the sound produced with
tight membrane has a higher pitch.
10. Give some applications of ultrasound?
Answer: To detect flaws in metals and structures in industries
To test the thickness of outer parts in industries
As a diagnostic tool in medical science
In relieving pain, in joints and muscles in medical science
11. What is pitch of the sound?
Answer: It is characteristic of sound depending upon its frequency. Different frequencies produce different pitch of
sound.
12 . What is called musical sound?
Answer: Sound is defined as sensation of hearing. Musical sound is one which gives a pleasant sensation to mind.
13. What are radio waves?
Answer: The types of waves which needed no medium to travel is called radio waves or Electromagnetic wave
Q. 14.You felt some irritation in her ears and
put a needle into her ears to remove it. Can it be dangerous?
Answer: It is very dangerous to put a sharp, pointed or hard thing
into our ears. It is so because outer part of the ear channels vibrations down
to a thin membranous structure called the eardrum which is stretched very
tightly and is flexible but delicate tissue. Any of the above mentioned objects
can damage the eardrum. Damaged eardrum in turn can impair the hearing process.
Q.15. Match the column :-
Column A
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Column B
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a. contraction
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i) coiled organ of hearing
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b. rarefaction
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ii) organs of
balance
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c. amplitude
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iii) compressed sound waves
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d. cochlea
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iv) loudness of
sound waves
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e. semicircular
canals
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v) expanded sound
waves
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Answer: a. iii, b. v, c. iv, d. i, e. ii.
Match the column :-
Animals audible range
Column A
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Column B
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a. cats
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i) 1 to 20000 Hz
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b. Elephants
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ii) upto 40000 Hz
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c. Moths
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iii) upto 50000 Hz
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d. Dogs
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iv) 100 to 60000 Hz
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e. Grasshoppers
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v) 1000 to 240000 Hz
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16. How does an ultrasound machine work in detecting
pregnancy or tumor?
Answer: Ultrasonic sound waves
have frequency higher than 20000 Hz and are used to investigate structures
inside human body. These waves can penetrate human tissue and get reflected
back. The reflected rays from the tissues are interpreted by the ultrasound
machine and shown on the monitor. So they can be used to check that a baby is
developing normally inside mother’s body or a tumour and its size in human body.
17. A Veena
player tunes his instrument before a concert. What is this tuning all about ?
Answer: A Veena player tunes his
instrument before a concert because if he wishes to raise the pitch of a
string, he must tighten the string since tighter string will vibrate faster to produce
high pitch of the sound while reverse will happen if he loosens string. Tuning
of stringed musical instrument means tightening or loosening the strings with the help of pegs
provided in it.
20. What is meant by echolocation? Is it useful?
Answer: Echolocation is a technique of detecting
objects with the help of sound waves. A bat flying in the dark uses echo
location where it produces high frequency sounds that bounce off objects in its
path and the bat hears echoes, which enable it to detect location of objects.
Sonar is a form of echolocation used by ships to detect echoes coming from
submerged objects. Geologists use sonar to find out oil deposits below the
surface of earth.
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