Sound Waves

Sound Waves

In physics, the sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid, or solid.

Effect of Humidity on the Speed of Sound Waves

The speed of sound is higher in humid, moist air than in dry air. This is why in the rainy season the sound is heard far and wide.

Frequency of Sound Waves

The frequency that a particle vibrates in a second is called frequency. Its S.I. unit is Hertz.

The frequency of a wave is equal to the frequency of the oscillation of the particles in the medium.

Types of Sound Waves

There are three types of sound waves

  • Infrasonic Waves.
  • Audible Waves.
  • Ultrasonic Waves.

Infrasonic Waves

Waves whose frequency is less than 20 Hz are called Infrasonic Waves. These waves are not heard by humans.

Audible Waves

Waves whose frequencies are between 20 Hz to 20,000 Hz are called Audible Wave. These waves are heard by humans.

Ultrasonic Waves

Waves with a frequency greater than 20,000 Hz are called Ultrasonic Wave. These waves are not heard by humans but are heard by dogs, villi, bats, etc.

Sound Waves
Uses of Ultrasonic Waves

Use of Ultrasonic Wave (1) Detection of ocean depths (2) Treatment of rheumatism (3) Sending signals (4) Destroying harmful bacteria of milk (5) Soot of factory chimneys Removal is done in (6) detecting human brain tumors and (7) cleaning parts of clocks.

Symptoms of Sound

The three characteristics of sound are – Intensity, Pitch, and .


The intensity of the sound is slow or slow, depending on the intensity of hearing. Its measurement unit is decibels.

The characteristic of a sound that causes differences in sounds of the same frequency is called .

Due to quality, a person recognizes and listens to hear his voice without seeing his acquaintances.


The characteristic of a sound that causes a sound to be thick or thin is called Pitch. The stringency depends on the frequency of the sound.

When the frequency of sound is high, the strings are high due to which the sound is thin ie melodious.

When the frequency of sound is low then the stellar is low due to which the sound is thick.

The frequency and sound of women are high due to which the voice of women is thin and melodious.

The lion’s roar and mosquito’s buzzing have more stringency than mosquitoes’ buzzing.

Sound Mixer
Sound Mixer

Intensity of Different Sound Sources

Sound Source Intensity (in decibels)
Simple conversation 30 to 40
Fast talk 50 to 60
Trucks, tractors 90 to 100
Orchestra 100
Missile 180
Machine gun 170
Motorcycle, electric motor 110
Siren 110 to 120

Refraction of Sound

When sound waves move from one medium to another, they deviate from their path, which is called the refraction of sound.


When the sound waves collide with a distant surface, this reflected sound is called resonance. This sound is heard again and again due to reflection. Like – the resonance is heard when shouting in the well.

The minimum distance between the listener and the reflective surface should be 16.44 m (about 17 m) to hear the resonance.

The resonance is used to measure the height of the aircraft, the depth of the ocean, and the distance to the mountain at a distance.


Even after closing the sound source in a closed place like a hall, the sound is heard for some time, which is called maintenance of a sound and the period of time the sound is heard is called the maintenance period. Like – thunder clouds.

Diffraction of sound

The wavelength of sound is of 01 meters. When an equal-grade blocker comes in the path of sound, the sound turns from the edge of the block and moves forward. This phenomenon is called the diffraction of sound.

Doppler,s Effect

When there is a relative motion between a sound source and a listener, the frequency of the listener’s sound is different from its actual frequency, which is called the Doppler effect.

Shock Wave

When the movement of a body becomes parabolic, that body leaves a conical disturbance in the medium behind it. The transmission of this disturbance is called Shock Wave.

MAC Number

The ratio of the speed of a body in a medium and the speed of sound in the same medium under the same conditions of temperature and pressure is called Mach number.

The speed of the body is supersonic when the Mach number is more than 01 and it is highly altitudinal when the Mach number is more than 05.


When the natural frequency of vibrations of an object is equal to the frequency of vibrations of a moving force, then that object starts vibrating with a much greater amplitude. This phenomenon is called Resonance.

Reflection of Sound

When the sound hits the surface and returns, this phenomenon is called Reflection of Sound.

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