9th Class Science Sound

Sound

Synopsis

• Sound:

Sound is a form of energy that produced due to vibration s of different object

• Sound is a wave motion produced by a vibrating source. A medium is necessary for its propagation as it is a mechanical wave. Sound cannot travel in Vacuum. The vibration source produces compression and refraction pulses which travel one after the other in the medium. Sound wave are longitudinal waves.

• The speed (v), frequency (f) and the wavelength \[(\lambda )\]of a sound wave are related by the equation:

\[V=f\lambda \]

• Characteristics of sound:

Pitch - Depends on the frequency. Higher the frequency, higher is the pitch

Loudness - Depends on amplitude, More the amplitude, more is the loudness.

Quality - Quality depends on the combination of harmonics produced by different instruments

• Mathematical equations involving wavelength\[(\lambda )\], time period (T), frequency (f) or (n)

(i) \[f=\frac{1}{T}\]  (ii)\[\lambda =vT\]   (iii) \[v=f\lambda \]

Where f is the frequency T is the time period,\[\lambda \] is the wavelength and v is the velocity of the wave

• Reverberation

Echo is the sound heard after reflection from a rigid obstacle (such as a cliff, a hill side wall of a building etc.) For example, echo is produced when you shout into a well inside an empty hall or inside a dome.

• Sonar

Sonar is a device that usess ultrasonic waves to measure the distance direction and speed of underwater objects.

• Audible range of frequencies: An average person can hear sounds in the frequency range of 20Hz-20kHz

• Infrasonic sound: Some vibrations produce sounds below the normal hearing range. These are known as infrasonic sounds (below 20Hz) Earthquakes underground nuclear explosions and tides, all produce infrasonic sound.

• Ultrasonic sound: Vibrations above the normal hearing range produce ultrasonic sound (above 20,000 Hz) Many animals like bats dolphins, dogs produce and hear such sounds.

• Sonic boom: An object travelling faster than the speed of sound is said to travelling at at supersonic speed. A source of sound travelling at supersonic speed causes the formation of shock waves. When a shock wave reaches a person, he hears a sharp and loud sound called the sonic boom.