# Characteristics of Sound Class-8th Goyal Brothers ICSE Physics Solution Chapter-7 Unit-1

Characteristics of Sound Class-8th Goyal Brothers Physics Solutions Chapter-7 (Sound), unit-1 (Characteristics of Sound). We Provide Step by Step Answers of Objective, True False, Incorrect and Correct, Fill in the blanks, Match the following , Short/Long Answer Type of Chapter-7 (Sound), unit-1 (Characteristics of Sound) Visit official Website  CISCE  for detail information about ICSE Board Class-8.

## Characteristics of Sound Class-8th Goyal Brothers ICSE Physics Solution Chapter-7 Unit-1

 Board ICSE Class 8th Subject Physics Book Name Goyal Brothers Chapter-7 Sound Unit-1 Characteristics of Sound Topic Solution of exercise questions Session 2023-24

### OBJECTIVE QUESTION

Characteristics of Sound Class-8th Goyal Brothers ICSE Physics Solution Chapter-7 Unit-1

#### Que: A. Fill in the blank spaces by choosing the correct words from the list given below:

List: ultrasonic, frequency, reflecting, sonar, amplitude

1. The device used to measure the depth of sea is called sonar.

2. For hearing an echo the minimum distance between the source of sound and the reflecting body is 17 m.

3. The range of ultrasonic vibrations is above 20,000 Hz.

4. The frequency of the sound produced by a vibrating wire decreases, if its length is increased.

5. The loudness of sound depends on the extent of amplitude of a vibrating body.

#### Que: B. Statements given below are incorrect. Write the correct statements :

##### Question: 1. The time taken by a vibrating body to complete one vibration is called frequency.

Answer: The time taken by a vibrating body to complete one vibration is called time period.

##### Question: 2. In order to produce an echo, the minimum distance between the source of sound and the reflecting body should be 14 m.

Answer: In order to produce an echo, the minimum distance between the source of sound and the reflecting body should be 17 m.

##### Question: 3. The characteristic of sound which distinguishes between the sharp sound and dull sound is called loudness.

Answer: The characteristic of sound which distinguishes between the sharp sound and dull sound is called pitch.

##### Question: 4. Shriller the sound more is the amplitude of body.

Answer: Shriller the sound more is the frequency of body.

##### Question: 5. Galton whistles are used to train animals.

Answer: Galton whistles are used to train dog.

#### Que: C. Write ‘True’ or ‘False’ for the following statements :

 Statements True/False 1. The range of sonic vibrations is between 20 Hz and 20,000 Hz. T 2. More the amplitude of a vibration, less is its loudness. F 3. With the increase in the frequency of a body, the sound becomes shrill. T 4. Subsonic waves are used in dish washing machines. F 5. Sound energy is reflected by soft and loose surfaces. F

#### Que: D. Tick (√) the most appropriate answer:

##### 1. The number of vibrations made by a vibrating body in one second is called :

(a) wavelength

(b) frequency

(c) time period

(d) amplitude

Answer: option (b) frequency is correct.

##### 2. The frequency of ultrasonic waves is :

(a) less than 20 Hz

(b) between 20 and 10,000 Hz

(c) between 20 and 20,000 Hz

(d) above 20,000 Hz

Answer: option (d) above 20,000 Hz is correct.

##### 3. The frequency of sound increases when the closed length of an air column :

(a) increases

(b) decreases

(c) remains same

(d) none of these

Answer: option (a) increases is correct.

##### 4. The pitch of sound does not depend upon :

(a) thickness of vibrating wire

(b) area of cross-section of vibrating wire

(c) amplitude of vibrating wire

(d) length of vibrating wire

Answer: option (c) amplitude of vibrating wire is correct.

##### 5. Loudness does not change with the change in :

(a) frequency

(b) amplitude

(c) distance from source of sound

(d) presence of other reflectors

Answer: option (a) frequency is correct.

#### Que: E. Match the statements in Column A, with those in Column B :

 Column A Column B 1. A sound wave of frequency less than 20 Hz. (a) Quality of sound 2. The repetition of sound on reflection from some hill or high-rise building. (b) Sonar 3. An instrument used to measure the depth of sea. (c) Frequency 4. Number of vibrations made by a body in one second. (d) Echo 5. Term used to describe two sounds of same loudness and same frequency, yet they can be distinguished from each other. (e) Infrasonic

 Column A Column B 1. A sound wave of frequency less than 20 Hz. (a) Infrasonic 2. The repetition of sound on reflection from some hill or high-rise building. (b) Echo 3. An instrument used to measure the depth of sea. (c) Sonar 4. Number of vibrations made by a body in one second. (d) Frequency 5. Term used to describe two sounds of same loudness and same frequency, yet they can be distinguished from each other. (e) Quality of sound

### STUDY QUESTION

Characteristics of Sound Class-8th Goyal Brothers ICSE Physics Solution Chapter-7 Unit-1

#### Question: 1. Define the following terms used in the study of sound :

##### (a) Amplitude

Answer: The amplitude of a sound wave is the measure of the height of the wave. The amplitude of a sound wave can be defined as the loudness or the amount of maximum displacement of vibrating particles of the medium from their mean position when the sound is produced.

##### (b) Frequency

Answer: Sound moves through a medium such as air or water as waves. It is measured in terms of frequency and amplitude. Frequency, sometimes referred to as pitch, is the number of times per second that a sound pressure wave repeats itself.

##### (c) Time period

Answer: The time taken by a wave to complete one oscillation is called as time period. SI unit to measure time period is second (s).

#### Question: 2. Derive a mathematical relation between the frequency and the time period of a sound wave?

Answer: The relation between period and frequency is Time = 1 / Frequency.

#### Question: 3. What name is given to the sound waves of frequency (a) less than 20 Hz, (b) between 20 Hz and 20,000 Hz (c) above 20, 000 Hz. Which waves among the above are not audible to human ear?

Answer: Sound waves above 20,000 Hz are ultrasonics. Sound waves below the frequency of 20Hz are infrasonics. Both are inaudible sounds for humans. Sound waves between 20Hz to 20,000Hz are audible sounds.

#### Question: 4. Name three animals who use ultrasonic waves. Explain atleast one animal which uses ultrasonic waves?

Answer: Ultrasonic sound waves are the waves having frequency above 20,000 hertz. Animals such as bats, dos and dolphins can hear these high pitched sounds. So, the correct answer to this question is dogs, bats and dolphins.

#### Question: 5. (a) Define monotone properly?

Answer: A sound with a single fixed frequency is called monotone. Sound produced by a vibrating tuning fork produces monotone which is the sound of a single frequency. frequency of a monotone does not vary.

#### (b) State the unit of loudness and write some loudness level and their effect of sound on human ear?

Answer: It is directly proportional to the square of the amplitude of vibration. If the amplitude of the sound wave becomes double, then the loudness of the sound will be quadrupled. It is expressed in decibel (dB). Sounds above 80 dB becomes noise to human ears.

#### Question: 6. (a) State two laws of reflection of sound?

Answer: State two laws of reflection of sound:

• The angle of reflection is always equal to the angle of incidence.
• The reflected sound, the incident sound, and the normal sound belong in the same plane.

#### (b) Name three different materials which reflect sound?

Answer: Zinc, copper and metal are the three different materials that reflect sound.

#### (c) Name three different materials which absorb sound?

Answer: clothes, paper and foam are the three different materials that absorb sound.

#### Question: 7. (a) What do you understand by the term echo?

Answer: Echo is a reflection of sound that arrives at the listener with a delay after the direct sound. The delay is proportional to the distance of the reflecting surface from the source and the listener. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room.

#### (b) State two conditions for the formation of an echo?

Answer: The necessary conditions for the formation of an echo:

(i) The minimum distance between the source of sound and the reflecting body should be 17 meters.

(ii) The wavelength of sound should be less than the height of the reflecting body.

#### Question: 8. (a) What is a sonar?

Answer: Sonar stands for sound navigation and ranging. Sonar would be described as the method of estimating the distance as well as the orientation of underwater structures or entities using sound waves.

#### (b) To what use sonar is put? Explain clearly?

Answer: NOAA scientists primarily use sonar to develop nautical charts, locate underwater hazards to navigation, search for and map objects on the seafloor such as shipwrecks, and map the seafloor itself. There are two types of sonar—active and passive.

#### Question: 9. (a) What do you understand by the term loudness of sound?

Answer: The loudness of a sound is a phenomenon that occurs when the amplitude of the sound wave changes. The sound is said to be loud if the amplitude of the sound wave is large. The loudness of sound is proportional to the square of the vibration amplitude and is measured in decibels.

#### (b) State two physical factors which determine loudness of sound?

Answer: There are two factors that determine how intense a sound is: the size of the sound waves and the distance from their source:

• Sound waves are measured according to their amplitude.
• Wave amplitude is determined by the energy that caused them.

#### Question: 10. (a) What do you understand by the term pitch of sound?

Answer: Pitch, in music, position of a single sound in the complete range of sound. Sounds are higher or lower in pitch according to the frequency of vibration of the sound waves producing them.

#### (b) State one factor which determine pitch of sound.

Answer: Pitch of the note is determined by the frequency of sound. More is the frequency of sound, more is the pitch of sound and vice-versa.

#### Question: 11. What do you understand by the term quality of sound? How is quality imparted to a sound of some particular pitch and loudness?

Answer: The quality or timbre of sound is that characteristic which enables us to distinguish one sound from another having the same pitch and loudness. The sound which is more pleasant is said to be of a rich quality.

The two main properties of sound are frequency and amplitude. The frequency of the sound waves determines the pitch of the sound. The amplitude of sound determines the loudness. The quality of sound is affected by the pitch and the loudness.

— : end of Characteristics of Sound Class-8th Goyal Brothers ICSE Physics Solution Chapter-7 Unit-1:–-