Short and Concise Class 8 Sound Notes

Firstly, let us see what we are going to study in this chapter. The overview of the chapter is very necessary for every student. This gives you an idea about the content we are going to study and can also relate to our previous syllabus or chapters.

Class 8 Sound Notes
Sound Notes Class 8
Overview: Chapter 13 Sound

Let us first see what we are going to study-

Here is the list of topics we are going to discuss in this chapter 13 Sound.

  1. What is Sound?
  2. Sound Production
  3. Propagation of Sound
  4. Time Period
  5. Frequency
  6. Amplitude
  7. Characteristics of Sound
    1. Pitch
    2. Loudness
    3. Quality of Sound
  8. How do Humans Speak?
  9. Human Ear
  10. Noise and Music
  11. Causes Noise Pollution
  12. Effects of Noise Pollution
  13. Prevention of Noise Pollution
  14. Echo
  15. Application of Echo

Sound Notes Class 8 | Short and Concise

What is Sound?

A sound is a form of energy that helps us to communicate with each other.

Question: What type of energy is Sound?

Answer: Sound is form of both Kinetic Energy and Potential Energy. (Kinetic>Potential).

In other words, Sound is a mechanical wave (longitudinal wave) that is produced by a vibrating source.

Knowledge Booster:

A wave is a disturbance.

Longitudinal Wave: The type of wave in which particles vibrate in the direction of the motion of the wave.

For More About Longitudinal and Transverse Waves: Click Here to Read

Production of Sound

Sound is produced when the source vibrates or the object producing the sound vibrates.

Vibration: Vibration is the to and fro or back and forth motion. The best example is the motion of the pendulum about its mean central position.

Propagation of Sound

Now, let us talk about the propagation of sound waves.

What is propagation of sound?

The propagation of sound takes place in a medium.

The propagation of sound takes place in all the mediums- solid, liquid, and gas.

The propagation of sound waves is faster in Solids than Liquid and Gas.

SOLID > LIQUID > GAS

Amplitude

Amplitude Meaning

The definition of Amplitude says it is the maximum displacement of a particle from its mean position.

Time Period

It is the time taken to repeat an event or It is the time taken to complete one vibration or oscillation.

Frequency

It is the number of events occurring in a second or It is the number of oscillations or vibrations taking place in 1 second.

In other words, it is the number of waves (in this case sound wave) passing a fixed point in a unit time.

Frequency can also be defined as the number of cycles in unit time or one second.

Unit of Frequency: Hertz (Hz)

Note: per second (1/second) = Hertz

Characteristics of Sound

The characteristics of sound helps us to distinguish different sounds coming from different sources of Sound.

The characteristics that help us to distinguish the sounds are – Loudness, Pitch and Quality.

Loudness

Two sounds can be differentiated with the help of loudness, and depends upon the sound energy. Greater the sound energy, larger is the loudness.

  • The Loudness of the Sound depends on the Amplitude of the Sound wave.
  • Loudness is measured in decibel (dB).
  • The drop of a pin is considered 0 dB.
  • When we increase the volume, we increase the amplitude.
  • When we decrease the volume we decrease the Amplitude.

Loudness depends upon the following factors- 

  1. Amplitude
  2. Area of vibrating body (Larger Area means larger loudness)
  3. Distance from the sound source (With distance loudness decreases)
  4. Density of the medium (Solid>Liquid>Gas)

Pitch

Two sounds having same loudness (Amplitude) can be differentiated with the help of Pitch.

Pitch helps in distinguishing Shrill Sound (thin Sound) from a Grave Sound (Thick or Heavy Sound).

  • Pitch of a sound depends on the frequency of sound.
  • Shrill Sound produces high frequency whereas Grave Sound produces low frequency.
  • High pitched sound has high frequency.
  • Low pitched sound has ow frequency.
  • Examples of High Frequency Sound- Sounds of Women, Birds, Cat, Babies
  • Examples of Low Frequency Sound- Sounds of Men, Dogs, Frog

Quality of Sound (Timbre)

Quality of sound which is also called Timbre, helps in distinguishing two sounds of the same Pitch and Loudness.

  • Different sources have different Quality of Sound because of the Waveform.
  • Quality of Sound is related to Music.

How do Humans Speak?

  • Humans speak with the help of a voice box also called Larynx.
  • The voice box has two Vocal Cords and a Slit in between them.
  • When the exhaled air passes through this slit, the two Vocal Cords vibrates (just like air passing through two paper folds) and thus produces sound.
  • The type of sound, i.e., high pitched or low pitched, depends upon the size of the vocal cords.
  • The size of Vocal cords in Women have 15 mm.
  • The size of Vocal cords in Men have 20 mm.

Human Ear

The Human Ear can be divided into two three parts- Outer Ear, Middle Ear, and Inner Ear.

Outer Ear: The outer ear consists of Pinna, Ear canal and Eardrum (a stretched membrane).

  • Eardrum separates the outer ear from the middle ear.

Middle Ear: It has three interlocked delicate bones- Malleus (Hammer), Incus (Anvil), and Stapes (Stirrup).

  • The vibration of eardrum makes these bones vibrate.

Inner Ear: It consists of a Cochlea and Auditory Nerves.

  • Cochlea: It is a snailed shaped organ filled with a fluid that moves in response to the vibrations.
  • Auditory Nerves: It consists of bundle of nerve fibres that carries hearing information from inner ear (Cochlea) to the brain.

Noise and Music

Music

  • Music is the sound that is pleasant to our ear.
  • Any sound that has a loudness below 30 dB is considered Music.
  • The waveform of Music is- Regular, Smooth, Continuous, and periodic.

Noise

  • Noise is the sound that is not pleasant to our ear.
  • Any sound that has a loudness above 120 dB is considered Noise.
  • The waveform of Music is- Irregular, harsh, discontinuous, and non-periodic.

Noise Pollution

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Causes Noise Pollution

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Effects of Noise Pollution

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Prevention of Noise Pollution

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Echo

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Application of Echo

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