Analysing Sound Waves

1. Sounds are mechanical waves. They are caused by vibrating objects. Hence, all vibrating objects produce sound. As an example: The strings of a guitar, the skin of a drum and a tuning fork vibrate to produce sound.


2. By using a loudspeaker as an example,  the vibrating cone of a loudspeaker produces sound by vibration.

3. Its vibrating diaphragm is continually compressing and stretching the air next to it.

4. This produces a series of compression and rarefaction travel through the air away from the loudspeaker.

5. Compression is a region of increased pressure and rarefaction is region of decreased pressure. The resulting succession of compression and rarefaction makes up the sound waves.



6. Sound wave is longitudinal in nature because the air molecules vibrate in a direction which is parallel to the direction of propagation is essentially due to the vibration of molecules of its medium.

7. Compression and rarefaction need a material which can be compressed and stretched. This explains why we do not hear any sound from the outer space which mainly consists of vacuum.

Amplitude and Frequency of Sound Waves

1. The amplitude of sound waves depends on its loudness. The louder the sound, the bigger is its amplitude.

2. The frequency of sound waves depends on its pitch. The higher the pitch of the sound, the higher is its frequency.

Applications of sound waves

1. Sound can be generated at a wide range of frequency.

2. Sound waves generated between 20 Hz and 20 kHz can be heard by normal human ears and are known as audio waves.

3. Those below 20 Hz are called infrasound and those above 20 kHz are known as ultrasound.

4. A bat can navigate in complete darkness by emitting very high-pitched sound waves in the ultrasonic range. When the waves hit a nearby object, they are reflected and received by the bat. The time lag between the emission of the sound waves and sensation of the reflected waves helps  the bat to estimate the position of the object accurately. The bat then adjust its direction to avoid knocking the object.

5. Dolphins use ultrasonic frequency of about 150 kHz for communication and navigation.

6. Ultrasonic rulers in ships use ultrasonic echoes to measure distance.

7. High intensity ultrasonic shockwaves can be used to break kidney stones.

8. Opticians and goldsmiths use ultrasonic cleaner to clean spectacles, jewellery and ornaments. The water used for the cleaning purpose is vibrated by ultrasound. The vibrations shake off dirt attached to these objects.

9. Dentists also use ultrasonic beams to vibrate and shake off dirt and plaque off the the teeth of patients.