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

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.

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

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

(d) The frequency is measured in second.

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

(f) The pitch of sound depends on frequency.

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

### 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.

### 4. Select the correct alternative

(a) Sound can not travel in

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

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.

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

0 to 80 dB

(d) The unit of loudness is

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

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 .

using thicker string

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

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#### Question-1 :-

How does sound travel in air?

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?

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.

• 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.

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

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.

#### 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.

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

(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?

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.

(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

(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

(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?

(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?

(i) Loudness ∝ (amplitude)2

Loudness is proportional to amplitude square Ratio of loudness  =

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

#### Question-2 :-

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

(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

Thanks