Sound – Production and Propagation of Sound
* Sound is form of energy that produces the sensation of hearing in our ears.
* Sound is produced due to the vibration of objects.
* Intensity of sound is the amount of sound energy incident per unit time per unit area.
* Sound propagates through a medium.
* A wave is disturbance that moves through medium set neighbouring particles into motions.
Wave form are categorised into two types:
* Transverse waves
* Longitudinal waves
In a longitudinal wave:
* A compression is a region of high pressure.
* A rarefaction is a region of low pressure.
* Sound waves in air are longitudinal waves.
* The wavelength is the distance between two consecutive compressions or two consecutive rarefactions. It is denoted by λ.
* The time period is the interval between two successive or two successive rarefactions. It is denoted by T.
* The frequency is the number of waves produced in a unit, ‘T’. It is denoted by
‘n’: n = 1/T
* Pitch is the interpretation of frequency of a sound by brain.
* The amplitude is the maximum displacement of the vibrating particles from their mean position. It is denoted by A.
* The speed of a wave is the ration of its wavelength to its time period or the product of its frequency wavelength. It is denoted by v.
v = λ/T = nλ
* The quality or timbre is the characteristic that distinguishes a sound from other sounds with the same pitch or loudness.
* A tone is a sound of a single frequency.
* A note is a sound produced due to blend of several frequencies.
* The speed of sound of sound in a medium depends on the properties of the medium through which it propagates.
* Supersonic speed is the speed of an object when it travels in air at speed faster than that of sound in air. The sharp and loud sound produced by a supersonic object is called a sonic boom.
Reflection of Sound and Echo
* When a sound wave is incident on a hard surface, it bounces back into the same medium. This is known as the reflection of sound.
* Echo is the repetition of sound that results when a sound wave reflects from a surface.
* The minimum distance required to hear an echo is 17.2 metres (velocity of sound = 344 m s-1).
* Multiple reflection of sound is the success reflection of sound from various reflecting surfaces.
* The phenomena of persistence of sound in a closed enclosure, due to multiple reflections are called reverberation.
* The ear converts audible frequencies in air into electric impulses that reach the brain.
* Hearing aids helps us compensate for reduction in our auditory capabilities.
* A human ear can hear sounds ranging from 20 hertz to 20000 hertz.
Sound waves are classified into three categories based on their frequencies.
* Infrasonic sounds (0 to 20 hertz)
* Audible sounds (20 hertz to 20000 hertz)
* Ultrasounds (above 20000 hertz)
* Ultrasound waves have a wide range of applications in the medical and industrial field.
* SONAR stands for Sound Navigation and Ranging. Sonar is a device that uses ultrasonic waves to measure the distance, direction and speed of underwater objects.
* The distance travelled by the ultrasound ray is given by the equation: 2d = v x t
Where:
d = Distance from the ship to the seabed
v = Speed of sound waves
t = Time taken by the sound wave to get back.