Sound Waves

Often we hear sound when we talk to people, listen to music, play a musical instrument, etc. But have you ever wondered what is sound and how is it originated? Or why do we hear our own voice when we shout in a big empty room? In this article, let us find answers to all these questions.

What Is Sound?

A sound is a vibration that propagates through a medium in the form of a mechanical wave. The medium in which it propagates can either be a solid, a liquid or a gas. Sound travels fastest in solids, relatively slower in liquids and slowest in gases. A sound wave is the pattern of disturbance caused by the energy traveling away from the source of the sound. Sound waves are longitudinal waves. This means that the propagation of vibration of particles is parallel to the direction of the energy wave propagation. When the atoms are set in vibration they move back and forth. This continuous back and forth motion result in a high-pressure and a low-pressure region in the medium. These high- pressure and low-pressure regions are termed as compressions and rarefactions, respectively. These regions are transported to the surrounding medium resulting in the sound waves to travel from one medium to another.

Nature Of Sound

The sound produced by a guitar is different from the sound produced by a drum. This is because the sound produced by different sources have different characteristics. Sound can be characterised by its frequency, wavelength and amplitude.

  • Frequency of sound

The number of rarefactions and compressions that occur per unit time is known as the frequency of a sound wave. Mathematically, the frequency of a wave is denoted as follows:

f=1/T

Where f is the frequency of a sound wave and T is the time period.

  • Wavelength of sound

The distance between the successive compression and rarefaction is known as the wavelength of a sound wave. The wavelength is mathematically represented as follows

λ=v/f

Where f is the frequency of the sound wave and v is the velocity of the sound wave.

  • Amplitude of sound

The amplitude of the sound is the magnitude of the maximum disturbance in a sound wave. The amplitude is also a measure of the energy. Higher the amplitude higher the energy in a sound wave.

Humans can hear a limited range of frequencies of sound. Physicists have identified the audio frequency spectrum of the human ear to be between 20 Hz and 20,000 Hz. Under ideal laboratory conditions, the human ear can detect frequencies that are as low as 12 Hz and as high as 20,000 Hz.

Speed  of Sound

The speed at which sound waves propagate through a medium is known as the speed of sound. The speed of sound is different in different media. The speed of sound is highest in solids because the atoms in solid are highly compressed. The interaction between atoms in a particle is highly dependent on the distance between them. Higher the interaction between the atoms, the quicker the energy is transferred. As the interaction of the particles in solids is high, the speed of sound is faster than liquids and gases. The table below lists the speed of sound in different media. The speed of sound is calculated using the formula

c=d/t

Where d is the distance travelled by sound and t is the time taken to cover the distance.

Medium

Speed of sound

Water

1481 m/s

Air

343.2 m/s

Copper

4600 m/s

Hydrogen

1270 m/s

Glass

4540 m/s

Reflection Of Sound

Reflection of sound is similar to the reflection of light. The reflection of sound obeys the following laws of reflection

  • The angle of incidence is equal to the angle of reflection.
  • The incident sound, the normal sound and the normal sound all lie in the same plane.

When a sound hits a hard surface, it reflects back to its source. This reflection of sound is otherwise is called an echo. Hard surfaces have a tendency to reflect sound while soft surfaces absorb sound and silence them. If the frequency of the sound wave is low, then the sound wave will not get reflected. Sometimes, we hear multiple echoes from a source of sound if the area is large and has multiple reflecting surfaces such as valleys and huge empty rooms. This phenomenon is known as reverberation.

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Sound can travel through