ICSE Selina Class 8 Physics Chapter 7 – Sound explains how vibration or the back and forth movement of an object produce sound. The solutions of the ICSE Selina publication for Class 8 covers all the questions given in the Selina Publication for class 8 in that particular chapter. The answers provided in these Solutions by BYJU’S are accurate and precise in the examination point of view.
The form of energy produced by a vibrating object is known as Sound. The to and fro motion of an object is called vibration. A material medium is required for the propagation of sound. As there is no material in the vacuum, sound cannot propagate through it.
Different components that you learn in this chapter are:
- Amplitude: Maximum displacement of a vibrating particle from its mean position.
- Time period: The time taken for a vibrating particle to complete one full oscillation.
- Frequency: The number of vibrations per second.
Characteristics of Sound: The sound originated by any means have the following characteristics, namely, loudness, pitch or shrillness, and quality or timbre. The chapter deals with all these attributes in details
A. Objective Questions
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 the nearest rarefaction is called wavelength.
(d) The frequency is measured in second.
(e) The pitch of a sound depends on the amplitude of the wave.
(f) The pitch of a sound depends on the amplitude of the wave.
(g) Decibel is the unit of the pitch of a sound.
Fill in the blanks
(a) The time period of a wave is 2 s. Its frequency is 0.5S-1
(b) The pitch of a stringed instrument is increased by increasing tension in the string.
(c) The pitch of a flute is decreased by increasing the length of the 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 the sound of a single frequency.
Match the following
Column A Column B
(a) Amplitude (i) 1/time period
(b) Frequency (ii) amplitude
(c) Loudness (iii) maximum displacement
(d) Pitch (iv) presence of other frequencies
(e) Waveform (v) frequency
Column A Column B
(a) Amplitude (iii) maximum displacement
(b) Frequency (i) 1/time period
(c) Loudness (ii) amplitude
(d) Pitch (v) frequency
(e) Waveform (iv) presence of other frequencies
Select the correct alternative
(a) Sound can not travel in
Answer: The correct answer is 4. vacuum
(b) When sound travels in the form of a wave
1. the particles of the medium move from the source to the listener
2. the particles of the 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 correct answer is 4. 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: The correct answer is 1. 0 to 80 dB
(d) The unit of loudness is
Answer: The correct answer is 4. decibel
(e) In a piano, the pitch is decreased by
1. using a thicker string
2. increasing tension
3. reducing the length of string
4. striking it hard
Answer: The correct answer is 1. using a thicker string