Tuesday, October 16, 2012

CBSE Physics help class 8 Chapter: Sound Solved Questions for Exam

CBSE Physics help class 8 Chapter: Sound

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 


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
Column  B
a. contraction
 i) coiled organ of hearing
b. rarefaction
ii) organs of balance
c. amplitude
 iii) compressed sound waves
d. cochlea
iv) loudness of sound waves
e. semicircular canals
v) expanded sound waves

Answer: a. iii, b. v, c. iv, d. i, e. ii.              
Match the column :-
Animals audible range
Column  A
Column  B
a. cats
i) 1 to 20000 Hz
b. Elephants
 ii) upto 40000 Hz
c. Moths
iii) upto 50000 Hz
d. Dogs
iv) 100 to 60000 Hz
e. Grasshoppers
v) 1000 to 240000 Hz

Answer: a. iv, b. i, c. v, d. ii, e. iii.

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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