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

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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

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 :-

Question-2 :-

Question-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.

Question-8 :-

How is loudness related to the amplitude of wave?

Answer-8 :-

Amplitude determines the loudness of a wave. Greater the amplitude, greater is the loudness.

Question-9 :-

If the amplitude of a wave is doubled, what will be the effect on its loudness?

Answer-9 :-

The loudness of sound is directly proportional to the square of the amplitude of waves.
Loudness α (amplitude)² When the amplitude is doubled loudness becomes ( 2 )² = 4 times

Question-10 :-

How does the wave pattern of a loud note differ from a soft note? Draw a diagram

Answer-10 :-

Greater the amplitude, greater is the loudness.

The amplitude of soft notes is smaller than the amplitude of a loud sound.

Question-11 :-

Name the unit in which the loudness of sound is expressed?

Answer-11 :-

Loudness of sound is expressed in decibel (dB)

Question-12 :-

Why is the loudness of sound heard by a plucked wire increased when mounted on a sound board?

Answer-12 :-

A wire mounted on a soundboard is plucked, the surface area of vibrating air increases and sends forth a greater amount of energy, So the amplitude of vibration is large and louder is the sound

Question-13 :-

State three factors on which loudness of sound heard by a listener depends.

Answer-13 :-

THREE FACTOR FOR LOUDNESS OF SOUND:

1. Surface area of the sounding body. i.e. is directly proportional to the surface area of vibrating body.
2. On the distance of the source of sound, i.e. decreases with distance.
3. On amplitude of wave i.e. increases with amplitude.

Question-14 :-

What determines the pitch of a sound?

Answer-14 :-

FREQUENCY. A number of vibrations per second determine the pitch. Higher frequency, higher pitch means shrill sound. A ‘ low pitch has a flat sound.

Question-15 :-

Name the characteristic of sound related to its frequency

Answer-15 :-

Characteristic of sound related to its frequency is PITCH.

Question-16 :-

Name and define the characteristic which enables one to distinguish two sounds of same loudness, but of different frequencies, given by the same instrument.

Answer-16 :-

Sounds of different frequencies but of same loudness and timbre can be distinguished by the property called ‘pitch’ of sound.

The sensation of a frequency is commonly referred to as the pitch of a sound. A high pitch sound corresponds to a high-frequency sound wave and a low pitch sound corresponds to a low-frequency sound wave.

Question-17 :-

Draw a diagram to show the wave pattern of high pitch note and a low pitch note, but of the same loudness.

Answer-17 :-

 

Question-18 :-

How is it possible to detect the filling of a bucket under a water tap by hearing the sound standing at a distance?

Answer-18 :-

The pitch of the sound of water filling in a bucket increases as the water in the bucket rises, and the length of the area of the air column decreases. Hence, the frequency of the sound increases. Hence, from a distance it is possible to detect the filling of a bucket under a water tap.

Question-19 :-

The frequencies of notes given by flute, guitar and trumpet are respectively 400 Hz, 200 Hz and 500 Hz. Which one of these has the highest pitch?

Answer-19 :-

Frequency is directly proportional to pitch. Higher the frequency, higher the pitch. Hence, trumpet has the highest frequency of 500 Hz, and highest pitch.

Question-20 :-

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?

Answer-20 :-

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.

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

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

Answer-26 :-

(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 :-

(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 :-

(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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