MANGAL VIDYALAYAM, Petamitta.
Class: 8 PHYSICAL SCIENCE AY:2024-25.
Chapter: 13 SOUND
I. Important terms and definition:
1. Sound: A form of energy that travels as vibrations through air or another medium.
2. Amplitude: The maximum extent of vibration of a vibrating body from its mean
position is known as amplitude.
3. Frequency: The number of vibrations experienced by a vibrating body is known as
its frequency.
4. Time period: The time taken by a vibrating body to complete one vibration is
known as its time period.
5. Pitch: The shrillness or flatness of sound is called pitch.
6. Quality or Timbre: A characteristic which enables us to distinguish one sound
from another having the same pitch and loudness.
7. Echo: An echo is the sound that we hear after it has been reflected from a surface
at a distance .
8. Noise pollution: The presence of loud, unwanted and disturbing sound in our
environment
II. SHORT ANSWER TYPE QUESTIONS:
9. To increase the loudness of sound by four times, by how much should the
amplitude of vibration be changed ?
Ans:
1. Loudness is proportional to the square of amplitude.
2. Hence to increase the loudness of sound four times, the amplitude should be
doubled.
10. Give an example to show that light travels faster than sound.
Ans: Thunder and lightning occur simultaneously but we see the lightning first and
then hear the thunder. This shows that light travels faster than sound.
11. What factors decide the frequency of vibration of a plucked string?
Ans: The frequency of vibration of a stretched string depends on:
Thickness of the string
Length of the string
Tightness of the string
12. What factors decide the frequency of vibration of an air column?
Ans:
1. The frequency of vibration depends on the length of the air column.
2. A short air column produces a shrill note of higher frequency.
3. A long air column produces a flat note of lower frequency.
Class: 8 PHYSICAL SCIENCE AY:2024-25.
Chapter: 13 SOUND
I. Important terms and definition:
1. Sound: A form of energy that travels as vibrations through air or another medium.
2. Amplitude: The maximum extent of vibration of a vibrating body from its mean
position is known as amplitude.
3. Frequency: The number of vibrations experienced by a vibrating body is known as
its frequency.
4. Time period: The time taken by a vibrating body to complete one vibration is
known as its time period.
5. Pitch: The shrillness or flatness of sound is called pitch.
6. Quality or Timbre: A characteristic which enables us to distinguish one sound
from another having the same pitch and loudness.
7. Echo: An echo is the sound that we hear after it has been reflected from a surface
at a distance .
8. Noise pollution: The presence of loud, unwanted and disturbing sound in our
environment
II. SHORT ANSWER TYPE QUESTIONS:
9. To increase the loudness of sound by four times, by how much should the
amplitude of vibration be changed ?
Ans:
1. Loudness is proportional to the square of amplitude.
2. Hence to increase the loudness of sound four times, the amplitude should be
doubled.
10. Give an example to show that light travels faster than sound.
Ans: Thunder and lightning occur simultaneously but we see the lightning first and
then hear the thunder. This shows that light travels faster than sound.
11. What factors decide the frequency of vibration of a plucked string?
Ans: The frequency of vibration of a stretched string depends on:
Thickness of the string
Length of the string
Tightness of the string
12. What factors decide the frequency of vibration of an air column?
Ans:
1. The frequency of vibration depends on the length of the air column.
2. A short air column produces a shrill note of higher frequency.
3. A long air column produces a flat note of lower frequency.
