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Characteristics of Wave - Sound Notes - Class 9 PDF Download

Characteristics of sound wave:

Following are the main characteristics of sound wave:

  • Wavelength.

  • Amplitude.

  • Time period

  • Frequency

  • Velocity (Speed)

To discuss the characteristics of wave, a graphical representation of sound wave is considered.

Sound Wave Graphical Representation class nine CBSE NCERT

The peak of a wave is called compression or crest. The valley of a wave is called rarefaction or trough.

WAVELENGTH:

Wave length is the length between two consecutive peaks, i.e. crest or two consecutive valleys, i.e. trough of a wave. Wave length is represented by Greek letter λ (lambda).

Louder sound has shorter wavelength and softer sound has longer wavelength.

The SI unit of wavelength is metre (m).

AMPLITUDE:-

Magnitude of maximum disturbance on either side of the normal position or mean value in a medium is called amplitude. In other words, amplitude is the distance from normal to the crest or trough.

Amplitude of Sound Wave Graphical Representation class nine CBSE NCERT

Amplitude is the energy of sound. Louder sound has greater amplitude and softer sound has shorter amplitude. Thus, louder or softer sound is determined by its amplitude. Since louder sound has greater energy consequently greater amplitude, thus it travels to a longer distance. Softer sound has smaller energy consequently shorter amplitude, thus it travels to a shorter distance.

Amplitude is denoted by letter ‘A’. The SI unit of amplitude is metre (m).

TIME PERIOD:

Time required to produce one complete wave is called time period or time taken to complete on oscillation is called the time period of the sound wave. In other words, time in which a wave moves a distance equal to its wavelength is called time period.

The time period of sound wave is represented by letter ‘T’. The SI unit of time period is second (s).

FREQUENCY:

The number of sound waves produced in unit time is called the frequency of sound waves. For example, if a source of sound produces 20 sound waves in one second then the frequency is 20 Hz.

Time taken to calculate frequency is in second. Frequency is denoted by Greek letter ‘ν’ (nu). The SI unit of frequency is ‘hertz’.

This name had been given after the German Scientist Heinrich Rudolph Hertz.

Relation between time-period and frequency:

If 1 sound wave is produced by a source, in T second.

Relation between time period and frequency class nine sound cbse ncert

Where, ν = frequency and T = time period

Thus frequency is the reciprocal of the time period of wave. This means the frequency is increased with decrease in time and vice versa.

VELOCITY:

Distance covered by sound wave in unit time is called the velocity of sound wave.

Wave equation - sound - class nine cbse ncert

Therefore, velocity can be defined as distance travelled per second by sound wave.

Wave equation - sound - class nine cbse ncert1

Thus, velocity of sound wave = frequency X wavelength

This is called WAVE EQUATION. WAVE EQUATION is applied to all types of waves.

Thus, velocity of sound wave is the product of frequency and sound wave.

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FAQs on Characteristics of Wave - Sound Notes - Class 9

1. What are the characteristics of a sound wave?
Ans. The characteristics of a sound wave include frequency, amplitude, wavelength, and speed. Frequency refers to the number of vibrations or cycles per second and determines the pitch of the sound. Amplitude measures the intensity or loudness of the sound. Wavelength is the distance between two consecutive points on a wave and determines the size of the wave. Speed refers to how fast the wave travels through a medium.
2. How does frequency affect the pitch of a sound?
Ans. Frequency directly affects the pitch of a sound. Higher frequency sound waves have a higher pitch, while lower frequency sound waves have a lower pitch. For example, a high-pitched sound like a whistle has a higher frequency, while a low-pitched sound like a bass drum has a lower frequency.
3. What is the relationship between amplitude and loudness of a sound wave?
Ans. The amplitude of a sound wave determines its loudness or intensity. A larger amplitude means a louder sound, while a smaller amplitude means a softer sound. For example, when a guitar string is plucked harder, it vibrates with a larger amplitude and produces a louder sound.
4. How does the speed of sound vary in different mediums?
Ans. The speed of sound varies in different mediums. In general, sound travels faster in solids, then liquids, and slowest in gases. This is because the particles in solids are closer together, allowing sound waves to propagate more quickly. In contrast, particles in gases are more spread out, resulting in a slower speed of sound.
5. What happens to the wavelength of a sound wave when the frequency increases?
Ans. When the frequency of a sound wave increases, the wavelength decreases. This is because wavelength and frequency are inversely proportional to each other. As the frequency increases, the number of cycles per second increases, leading to shorter wavelengths. Conversely, if the frequency decreases, the wavelength becomes longer.
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