Characteristics of a Sound Wave

A sound wave is characterised by three factors:

1. Amplitude: It is the maximum disturbance caused in the medium from its rest position. It determines whether a sound is loud or soft. 

• Higher amplitude → Louder sound.
• Lower amplitude → Softer sound.

2. Frequency: It is the number of complete cycles (one compression + one rarefaction) produced per second.

`f="1" / "T"`

$T$: Time period (time taken for one complete cycle).

SI Unit: Hertz (Hz).

1 Hz = 1 cycle per second.

Example,

A tuning fork with a frequency of 512 Hz produces 512 compressions and rarefactions per second.

 Frequency determines the pitch of the sound.

• Higher frequency → Higher pitch (e.g., a whistle).
• Lower frequency → Lower pitch (e.g., a drum).

3. Speed: Speed of sound is the distance travelled by a compression or rarefaction in one second.

`v= "wavelength" / "time period"` = `lambda.f`

• $`v`$: Speed of sound
• λ: Wavelength
• `f`: Frequency

SI Unit: Metres per second (m/s)

Example,

Speed of sound in air = 343 m/s (at standard conditions).

Cycles of compression and rarefaction in a sound wave and change in air pressure

1. Compression: The upper part of the wave curve represents compression. It is a region where particles are close together, resulting in high pressure and high density.
2. Rarefaction (R): The lower part of the wave curve represents a rarefaction. It is a region where particles are spread apart, resulting in low pressure and low density.
3. Crest: The peak of the wave, representing maximum displacement in a compression.
4. Trough: The valley of the wave, representing maximum displacement in a rarefaction.

1. Wavelength (λ): It is the distance between two consecutive compressions or rarefactions. SI Unit: Metre (m).
2. Time Period (T): It is the time taken for two consecutive compressions or rarefactions to pass a fixed point. Or the time for one complete oscillation. SI Unit: Second (s).
3. Pitch: Pitch is how high or low a sound seems to a listener. Factors Affecting Pitch:

• Frequency of the sound wave.
• Size of the object producing the sound.
• Type of the object producing the sound.