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Sound ICSE Class-8th Concise Selina Physics

Sound ICSE Class-8th Concise Selina Physics Solutions Chapter-7. We Provide Step by Step Answer of Objective, True False , Fill in the blanks,Match the following, Short/ Long Answer Question and Numericals Type of Exercise-7 Sound. Visit official Website  CISCE  for detail information about ICSE Board Class-8.

Sound ICSE Class-8th Concise Selina Physics


 -: Select Topic :-

Objective Questions

Short/ Long Answer Question

Numericals Questions


A. Objective Questions Sound ICSE Class-8th Concise Selina

1. Write true or false for each statement

(a) When sound propagates in air, it does not carry energy with it.
Answer. False.

(b) In a longitudinal wave, compression and rarefaction are formed.
Answer. True.

(c) The distance from one compression to nearest rarefaction is called wavelength.
Answer. False.

(d) The frequency is measured in second.
Answer. False.

(e) The quality of a sound depends on the amplitude of wave.
Answer. False.

(f) The pitch of sound depends on frequency.
Answer. True.

(g) Decibel is the unit of pitch of a sound.
Answer. False.

 

2. Fill in the blanks

(a) The time period of a wave is 2 s. Its frequency is 0.5 S-1.
(b) The pitch of a stringed instrument is increased by increasing tension in string.
(c) The pitch of a flute is decreased by increasing length of air column.
(d) Smaller the membrane, higher is the pitch.
(e) If a drum is beaten hard, its loudness increases.
(f) A tuning fork produces sound of single frequency.

3. Match the following

Match the following

4. Select the correct alternative

(a) Sound can not travel in

  1.  solid
  2.  liquid
  3.  gas
  4.  vacuum

Answer

vacuum

(b) When sound travels in form of a wave

  1. the particles of medium move from the source to the listener
  2.  the particles of medium remains stationary
  3.  the particles of medium start vibrating up and down
  4.  the particles of medium transfer energy without leaving their mean positions.

Answer

the particles of medium transfer energy without leaving their mean positions.

(c) The safe limit of loudness of audible sound is

  1.  0 to 80 dB
  2.  above 80 dB
  3.  120 dB
  4.  above 120 dB

Answer

0 to 80 dB

(d) The unit of loudness is

  1.  cm
  2.  second
  3.  hertz
  4.  decibel

Answer

cm

(e) In a piano, pitch is decreased by

  1.  using thicker string
  2.  increasing tension
  3.  reducing length of string
  4.  striking it hard .

Answer

using thicker string


Short/ Long Answer Question Chapter-7 Sound Selina Physics for class-8

Page-136

Question-1 :-

How does sound travel in air?

Answer-1 :-

A periodic disturbance in the medium (Air) is created by the vibration of sound and the particles of the medium vibrate about their mean position and transfer of energy in the form of sound waves takes place, i.e. in the LONGITUDINAL WAVES

Question-2 :-

What is longitudinal wave?

Answer-2 :-

Longitudinal wave: The wave in which the particles of the medium vibrate about their mean positions in the direction of propagation of sound is called longitudinal wave. Such a wave can be produced in solids, liquids as well as gases.

Answer-5 :-

    • Frequency is the number of times a cycle is completed in a second.
    • The frequency & time period is inversely proportional.
      The number of vibrations per second is called frequency
      The s.i unit of frequency is Hertz.
    • The time taken to complete one vibration is called time period.

    Relationship between the Time Period (T) and Frequency (ƒ): By definition time period is the time taken to complete 1 vibration
    Or
    In time T, the number of vibration= 1
    ∴ In 1 second, the frequency or number of vibrations = 1 / T
    ƒ = 1/t or t= 1/ƒ

Question-6 :-

Name three characteristics of a musical sound.

Answer-6 :-

Sounds can be distinguished from one another by the following three different characteristics:

  1. loudness
  2. pitch or shrillness, and
  3. quality or timbre

Question-7 :-

Name the quantity from below which determines the loudness of a sound wave :
(a) Wavelength
(b) Frequency, and
(c) Amplitude

Answer-7 :-

Quantity which determines loudness of a sound wave is (c) AMPLITUDE.

The air column determines the frequency of the sound produced, less air column produces increased frequency. Jar B has lesser air column above water and it will produce higher pitch.

 Figure shows two jars A and B containing water up to different heights. Which will produce sound of higher pitch when air is blown on them?

Question-21 :-

Two identical guitars are played by two persons to give notes of the same pitch. Will they differ in quality? Give reason for your answer.

Answer-21 :-

No two musical instruments of the same pitch have the same quality because pitch depends on the frequency or wavelength and quality depends on the waveform, upon the number or relative intensities of the different harmonics. Hence, the two notes are not of the same quality.

Question-22 :-

Two musical notes of the same pitch and same loudness are played on two different instruments. Their wave patterns are as shown in figure.

How do they differ in (a) loudness (b) pitch and (c) quality

Two musical notes of the same pitch and same loudness are played on two different instruments. Their wave patterns are as shown in figure.

Answer-22 :-

(a) Loudness of each is the same as the amplitude is the same.

(b) Pitch of each is the same.

(c) Quality is different as the wave form is different.


(Page-137)

Question-23 :-

Which characteristics of sound makes it possible to recognize a person by his voice without seeing him?

Answer-23 :-

Timbre and pitch are the characteristics of sound that make it possible to recognize a person by his voice without seeing him.

Question-24 :-

State the factors that determine

(a) The pitch of a note

(b) The loudness of the sound heard

(c) the quality of the note.

Answer-24 :-

(a) Frequency

(b) Amplitude

(c) Waveform

Question-25 :-

Name the characteristics of the sound affected due to a change in its

(a) amplitude (b) waveform (c) frequency

Answer-25 :-

(a) Loudness

(b) Quality

(c) Pitch

Question-26 :-

Figure shows four waves A, B, C, and D

Name the wave which shows (a) a note from a musical instrument (b) a soft note (c) a shrill note

Name the wave which shows (a) a note from a musical instrument (b) a soft note (c) a shrill note

Answer-26 :-

Name the wave which shows (a) a note from a musical instrument (b) a soft note (c) a shrill note

(a) a note from a musical instrument is shown by figure (d);

(b) a soft note is shown by figure (a);

(c) a shrill note is shown by figure (c)

Question-27 :-

How is the pitch of sound in a guitar changed if

(a) thin wire is used,

(b) wire under less tension is used?

Answer-27 :-

(a) Higher pitch is obtained

(b) Low pitch is obtained.


Numericals  Question Chapter-7 Sound Selina Physics for class-8

(Page-137 )

Question-1 :-

Two waves of the same pitch have amplitudes in the ratio 1: 3 What will be the ratio of their (i) loudness, (ii) pitch?

Answer-1 :-

(i) Loudness ∝ (amplitude)2

Loudness is proportional to amplitude square Ratio of loudness  =

Two waves of the same pitch have amplitudes in the ratio 1: 3 What will be the ratio of their (i) loudness, (ii) pitch?

(ii) Frequency of the sound wave has no effect on amplitude.
so, frequency remains the same if the pitch is unchanged.

selina physics class 8 ch 7 sound numerical ans no 1 b

Question-2 :-

Two waves have frequencies 256 Hz and 512 Hz, but same amplitude. Compare their (i) loudness, and (ii) pitch

Answer-2 :-

(i) LOUDNESS :
∴ Amplitude of two waves is the same
∴ their loudness is the same i.e. in 1:1

(ii) PITCH :
Ratio of frequencies
256 Hz: 512 Hz
∴ Ratio of their pitch =1:2

 

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