Goyal Brothers Sound Class-9 ICSE Physics Ch-9

Goyal Brothers Sound Class-9 ICSE Physics Ch-9.  We Provide Step by Step Answer of Exercise, Subjective Sound  Class-9, Visit official Website CISCE  for detail information about ICSE Board Class-9 Physics.

Goyal Brothers Sound Class-9 ICSE Physics Ch-9


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Exercise Objective Questions

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 Subjective Questions

Practice Problems


Exercise Objective Questions

Goyal Brothers Sound Class-9 ICSE Physics Ch-9

Multiple Choice Questions.
Select the correct option :

1. In case of longitudinal waves, the particles of the medium vibrate :
(a) in the direction of wave propagation
(b) opposite to the direction of wave propagation
(c) at right angles to the direction of wave propagation
(c) none of the above
Ans. (a) in the direction of wave propagation

2. A longitudinal wave consists of :
(a) crest and trough in the medium
(b) compression and rarefaction in the medium
(c) both (a) and (b)
(d) neither (a) nor (b)
Ans. (b) compression and rarefaction in the medium

3. The longitudinal waves can propagate only in .
(a) solids
(b) liquids
(c) gases
(d) all of these
Ans. (d) all of these

4. A part of the longitudinal wave in which particles of the medium are closer than the normal particles is called :
(a) rarefaction
(b) crest
(c) trough
(d) compression
Ans. (d) compression

5. A part of longitudinal wave in which particles of the medium are farther away than the normal particles is called :
(a) rarefaction
(b) trough
(c) compression
(d) crest
Ans. (a) rarefaction

6. In the region of compression or rarefaction, in a longitudinal wave, the physical quantity which does not change is :
(a) pressure
(b) mass
(c) density
(d) volume
Ans. (b) mass

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7. The wavelength is the linear distance between the :
(a) two consecutive compressions
(b) two consecutive rarefactions
(c) one compression and one rarefaction
(d) both (a) and (b)
Ans. (d) both (a) and (b)

8. The number of oscillations passing through a point in unit time is called :
(a) vibration
(b) frequency
(c) wavelength
(d) amplitude
Ans. (b) frequency .

9. The SI unit of frequency is
(a) hertz
(b) gauss
(c) decibel
(d) none of these
Ans. (a) hertz

10. If the frequency of a wave is 25 Hz. the total number of compressions and rarefactions passing through a point in 1 second is :
(a) 25
(b) 50
(c) 100
(d) none of these
Ans. (b) 50

11. Which of the following is an elastic wave?
(a) light wave
(b) ratio wave
(c) sound wave
(d) microwave
Ans. (c) sound wave


 Subjective Questions

Goyal Brothers Sound Class-9 ICSE Physics Ch-9

Question 1.

(a) What do you understand by the term sound energy?
(b) State three conditions necessary for hearing sound.

Answer:
(a) Sound energy : “It is a form of energy that produces the sensation of hearing in our ears.” Sound is produced when a body vibrates.
(b) Necessary conditions for hearing sound :

  1. There must be a vibrating body, capable of transferring its energy to its surroundings.
  2. These must be a material medium to pick the energy and then propagate it in forward direction.
  3. There must be a receiver, so as to receive the sound vibrations and then transmit them to the brain for final interpretation, such as human ear.

Question 2.
Describe briefly an experiment to prove that vibrating bodies produce sound.
Answer:
Experiment : Take a tuning fork. It is U-shaped fork made of steel provided with a handle.
 Take a tuning fork. It is U-shaped fork made of steel provided with a handle.
Strike the tuning fork with a rubber hammer and hold it close to ear. A sound is heard. Now take a freely suspended pith ball and touch one end of the tuning fork (which is already hit with a rubber hammer) to it. It is observed that pith ball repeatedly flies outward. This experiment too proves that sound is produced by a vibrating body.

Question 3.       (Goyal Brothers Sound Class-9 ICSE Physics)

(a) What do you understand by the term infrasonic vibrations?
(b) What do you understand by the term sonic vibrations? State the range of sonic vibrations for the human ear.

Answer:
(a) Infrasonic vibrations : Those vibrations whose frequency is less than 20 hertz are known as infrasonic vibrations
(b) Sonic vibrations : Sonic vibrations are also known as audio vibrations.
Those vibrations whose frequency is from 20 hertz to 20000 hertz are known as sonic vibrations.
The range of sonic vibrations is from 20 vibrations per second to 20000 vibrations per second.

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Question 4.

(a) What do you understand by the term ultrasonic vibrations?
(b) Name three animals which can hear ultrasonic vibrations.

Answer:

(a) Ultrasonic vibrations : Those vibrations, whose frequency is more than 20000 hertz and are not perceived by human ear, are known as ultrasonic vibrations.
(b) Dogs, bats and dolphins can hear ultrasonic vibrations.

Question 5.
How do bats locate their prey during flight?
Answer:
Bats produce ultra sound which returns after striking an obstacle in their way. By hearing the reflected round, bats can judge the distance and direction of obstacle/prey in their way and hence bats can catch their prey during flight.

Question 6.
What is Galton’s whistle? To what use is it put?
Answer:
A special whistle which can produce ultra sound, not heard by humans, is called Galton’s whistle.
It is used to train dogs because they can hear ultrasounds upto a frequency of 40000 hertz.

Question 7.
State four practical uses of ultrasonic vibrations.
Answer:
Uses of ultrasonic vibrations :

  1. These are used for dissipating fogs on the runways at the airports.
  2. These are used in the ultrasound scanning of internal organs of human body.
  3. These are used for making dish washing machines. In these machines, water and detergents are vibrated with ultlrasonics vibrator. The vibrating particles of the dissolved detergent rub against the plates and clean them.
  4. These are used in SONAR (Sound navigation and ranging) to detect and find the distance of objects under water.

Question 8.
Describe an experiment to prove that material medium is necessary for the propagation of sound.
Answer:
A material medium is necessary for the propagation of sound. It can be proved with the help of following experiment :
An electric circuit consisting of a cell, a switch and an electric bell is arranged inside a bell-jar, which stands on the platform of an evacuating pump.
The switch of the bell is pressed to close the electric circuit. Sound is heard when there is air within the bell-jar. Air is now gradually pumped out of the bell-jar. The intensity of sound goes on decreasing, and no sound is heard when the air is completely removed from the bell-jar. It is because, the air which acts as a medium for the propagation of sound energy is removed.
 an experiment to prove that material medium is necessary for the propagation of sound.
From above experiment, it is clear that sound can not be heard in the absence of air i.e. a material medium is necessary for the propagation of sound.

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