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# Sound – Definition and Types

### Key Concepts

• Introduction to sound energy
• Sound wave
• Parts of sound wave

## Introduction to Sound

### Introduction:

Sound in the form of energy travels with decreasing amplitude. Sound is a mechanical wave; hence, it requires a medium (solids, liquids and gases) to propagate.

Unlike light, sound energy cannot travel through a vacuum.

### Important points of sound energy:

1. A sound is a form of energy.
1. It is a mechanical wave.
1. Sound needs a medium for the propagation.
1. Sound cannot travel through the vacuum.
1. It travels with decreasing amplitude.

### 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 a type of wave is called longitudinal wave.

In longitudinal waves, there are alternate compression and rarefactions.

### Compression:

If the particles in the wave are closer to each other in the longitudinal wave, then it is called compression.

### Rarefaction:

If the particles in the wave are far from each other in the longitudinal wave, then it is called rarefaction.

### Transverse wave:

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

In transverse waves, there are alternate crests and trough.

#### Crest:

The maximum displacement in a transverse wave is called a crest.

#### Trough:

The minimum displacement in a transverse wave is called a crest.

### Sound wave:

#### Amplitude:

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

The maximum displacement of the wave when plucked in the string, which is at rest, is called amplitude in longitudinal waves.

Amplitude is denoted by A, and units of amplitude are m(meter).

Note: Sound always travels with decreasing amplitude.

#### Wavelength:

The distance between a two consecutive crest or the trough or the distance between two consecutive compressions or the rarefaction is called wavelength.

The distance between the crest and the trough is called half of the wavelength, and the distance between compression and the rarefaction is also called half of the wavelength.

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 frequency units are Hz(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).

### Summary:

Sound in the form of energy travels with decreasing amplitude. Sound is a mechanical wave; hence, it requires a medium (solids, liquids, and gases) to propagate.

Unlike light, sound energy cannot travel through the vacuum.

#### 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 a type of wave is called 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 a type of wave is called longitudinal 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).

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