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# Sound and its Properties- Sound Waves

## Sound And Its Properties

### Key Concepts

• Vibrations and formation of sound
• Types of sounds
• Propagation of sound

### Sound wave:

Sound has two types of waves

1. Longitudinal wave
1. Transverse wave

#### Longitudinal wave:

The particles in the wave oscillate parallel to the way of propagation of the wave; such type of wave is called a longitudinal wave.

In longitudinal waves, there are alternate compression and rarefactions.

#### Transverse wave:

The particles in the wave oscillate perpendicular to the way of propagation of the wave; such type of wave is called a transverse wave.

In transverse waves, there are alternate crests and troughs.

#### Amplitude:

The maximum displacement or displacement of the wave from the mean position or equilibrium position is called amplitude transverse waves.

#### Wavelength:

The wavelength is between two consecutive crests, troughs, or two consecutive compressions or rarefaction.

Wavelength is denoted by λ(lambda), and units of the wavelength are m(meters) in the SI system.

#### Frequency:

The number of cycles per second is called frequency; the number of waves passing through the specific point is called a cycle.

Frequency is denoted by υ(nu), and units of the frequency are hertz.

#### Wave speed:

The distance travelled by the wave in the given amount of time is called wave speed.

Speed of wave = wavelength x frequency

Wave speed is denoted by meter Hertz (MHz).

### Formation of sound:

Every vibrating body produces sound.

Let’s consider a steel plate in the kitchen. If the plate is vibrated, then there is the production of sound which means that the vibrating body produces sound, and also after some time, the plate stops vibrating, and the sound will be disappeared. Those types of vibrations are called damped vibrations, which travel with decreasing amplitude are called damped vibrations.

### Important points of formation of sound:

1. Every vibrating produces sound.
1. If a body is at rest and not vibrating, then the body doesn’t produce sound.
1. Vibration with decreasing amplitude is called damped vibration.

### Types of sounds:

Depending upon the measurement of sound, sound has three types:

1. Infrasound
1. Normal sound
1. Ultrasound

### Measurement of sound:

The intensity of sound is measured in decibels. A human ear can hear sounds between 20 Hz to 20000 Hz.

### Infra-sound:

Sounds that are less than 20 Hz are called infrasound. The human ear cannot hear infrasound which has very little frequency.

### Audible sound:

Audible sounds are from 20 Hz to 20000 Hz. The human ear can hear normal sounds.

### Ultrasound:

Sounds that are more than 20000 Hz are called ultrasound. The human ear cannot hear ultrasound which has more frequency.

### Propagation of sounds:

Sounds can propagate from one point to another in a medium.

Propagation of sounds in

1. Solids
1. Liquids
1. Gases

### Propagation of sound in solids:

Particles in the solids are closely packed. If the particles are disturbed, then the disturbance will propagate very fast, as the particles are closely packed.

Hence, the speed of sound in solids is very high. The speed of sound in iron is 3960 m/s.

### Propagation of sound in liquids:

Particles in the liquids are moderately packed. If the particles are disturbed, then the disturbance will propagate at a medium pace, as the particles are moderately packed.

Hence, the speed of sound in liquids is moderate. The speed of sound in liquids is 1230 m/s.

### Propagation of sound in gases:

Particles in the gases are loosely packed. If the particles are disturbed, then the disturbance will propagate at a slow pace, as the particles are loosely packed, Hence the speed of sound in gases are slow, speed of sound in gases is 330 m/s.

## Summary

Formation of sound:

1. Every vibrating produces sound.
2. If a body is at rest and not vibrating, then the body doesn’t produce sound.
3. Vibration with decreasing amplitude is called damped vibration.

Measurement of sound:

The intensity of sound is measured in decibels. A human ear can hear sounds between 20 Hz to 20000 Hz.

Infrasound:

Sounds that are less than 20 Hz are called infrasound. The human ear cannot hear infrasound which has very little frequency.

Normal sound:

Normal sounds are from 20 Hz to 20000 Hz. The human ear can hear normal sounds.

Ultrasound:

Sounds that are more than 20000 Hz are called ultrasound. The human ear cannot hear ultrasound which has more frequency.

Propagation of sound in solids:

Particles in the solids are closely packed. If the particles are disturbed, then the disturbance will propagate very fast, as the particles are closely packed.

Propagation of sound in liquids:

Particles in the liquids are moderately packed. If the particles are disturbed, then the disturbance will propagate at a medium pace, as the particles are moderately packed.

Propagation of sound in gases:

Particles in the gases are loosely packed. If the particles are disturbed, then the disturbance will propagate at a slow pace, as the particles are loosely packed.

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