Sound Waves - Audible Wave, Infrasonic Wave, Ultrasonic Waves, Uses of Waves, Doppler effect, Mach number


Table of Contents: - Sound Waves, Audible Waves, Infrasonic Waves, Ultrasonic Waves, Doppler effect, Mach number, frequency Range of sound waves, Use of ultrasonic waves, Effect of heat, humidity, and air on the speed of sound, characteristics of sound wave (intensity, Quality, Reflection of sound, Refraction of sound, resonance, Reverberation, diffraction of sound, interference of sound), Doppler's Effect, sound boom.

What is a sound wave?:-  Sound is a longitudinal wave that originates from vibrating something, and produces sensation in our ears.

Frequency Range of Sound Wave/ Type of Sound Waves


#01. Audible sound waves: This is called audible sound.  human Can hear it. The Frequency range of Audible sound waves are between 20 Hz to 20,000 Hz.

#02. Infrasonic Waves: The frequency of the waves below 20 Hz are called Infrasonic Waves. The human cannot hear it. The elephant can hear these Infrasonic Waves.

#03. Ultrasonic waves: waves with a frequency range higher than 20,000 Hz are called ultrasonic waves. Dogs and bats can hear Ultrasonic waves & the human cannot hear it.



Use of Ultrasonic Waves


  1. To detect tumors in the body and to treat arthritis.
  2. In destroying harmful bacteria inside milk.
  3. In airplanes, cleaning of clock parts.
  4. In adding metals.
  5. SONAR (Sound Navigation and Ranging)- It is used in measuring the depth of the ocean.
Sound Waves - Audible, Infrasonic, Ultrasonic Waves, Doppler effect, Mach number
Sound Waves - Audible, Infrasonic, Ultrasonic Waves, Doppler effect, Mach number

Effect of pressure, heat, humidity, and air on the speed of sound


1. Pressure effect: If the temperature of the gas is constant then the change of pressure has no effect on the speed of sound.

2. Effect of heat: When the temperature of air increases by 1 ° C, the speed of sound is increased by 0.61 m / s.

3. Effect of humidity: The speed of sound in humid air is higher than its speed in dry air.

4. Effect of wind speed: If the wind is moving in the direction of sound then the sound waves accelerate & the speed of sound increases.

Speed ​​of sound in a different medium (m/s)

  1. Dry Air - 332
  2. Steam (100 ° C) - 405
  3. Hydrogen - 1269
  4. Carbon dioxide - 260
  5. Water - 1450
  6. Glass - 5640
  7. Aluminum - 6420
  8. Iron - 5100

Characteristics of the sound wave

Intensity: The intensity of a sound depends on the vibration amplitude of the vibrating object that produces the sound. The higher the amplitude of the vibration, the higher the sound intensity and hear the sound loudly.

Pitch: It is the characteristic of sound due to which the difference between thick and melodious sound is made. A high-pitched sound has a high frequency and a melodious sound, while low-pitched sound has a low frequency and a thick sound.

The Pitch of the sound of women is higher than those of men and the Pitch of mosquitoes are higher than those of lions. The intensity of sound has no relation to the Pitch of sound.

Quality: It is that characteristic of sound, on the basis of which differences can be made between sounds of equal intensity and the same frequency. The difference between the two sounds is due to differences in their original tones and harmonics.

Reflection of Sound: When the sound returns to the same medium after striking on the reflective surface, such a phenomenon is called a reflection of sound.

Echo: There is a reflected sound, which can be heard clearly. The minimum distance between the listener and the reflective surface must be about 17.2 m to hear the resonance. The effect of sound on the ear lasts for 1/10 seconds.

Refraction of Sound: When the sound waves go from one medium to another, their path deviates which is called refraction. Due to refraction, the sound is heard far away in the night than in the day.

Resonance: When the natural frequency of vibrations of an object is equal to the frequency of vibrations of a driving force, that object vibrates with maximum amplitude. This incident is called Resonance, due to resonance in 1939, the Tacoma bridge of the USA was damaged.

Reverbration: Even after closing the sound source in a hall, the sound is not stopped at all, but is heard for some time due to reflection. Such an event is called tracing. The time during which this sound persists is called the Reverbration time.

If the retention time of a hall is more than 0.8 seconds, then the speech of the speaker will not be heard clearly and if the retention time is zero then the hall is called a resonant hall.

Diffraction of Sound: This phenomenon is called diffraction when the sound waves turn on the edge of an obstacle in their path. Because of this, the sound coming from outside the room turns and reaches us.

Interference of Sound: When equal frequency and amplitude sound waves reach a point simultaneously, the redistribution of sound energy occurs at that point. This is called interference of sound. There are two types

i. Constructive interference: When both sound waves meet in the same phase, it is called Constructive interference. It has maximum sound intensity.


ii. Destructive Interference: When both sound waves are combined in opposite art, they are called destructive interference, which decreases the intensity of sound.

Doppler's Effect: The Doppler effect was propounded by John Doppler in 1842. According to Doppler, when there is a relative motion between a sound source and a listener, the frequency of sound is heard to the listener different from its actual frequency. This is called the Doppler effect.

Mach Number: The ratio of the speed of the body in a medium and the speed of sound in the same medium is called the Mach number.

Mach number = (speed of the body in a medium) / (speed of sound in the same medium)

If the MAC number is more than 1, then the body is called parasitic and if it is more than 5, it is called hyperpolar.

Sound Boom: The sound (the speed faster than the speed of sound) air produces a sound cone, which is called a strong wave. When this strong wave reaches the listener, he suddenly hears a kind of loud bang called a sound boom.