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Sound

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Introduction

A sound is a form of energy which gives the sensation of hearing. It is produced due to the vibration of a body. Acoustics is the study of sound waves. We hear various kinds of sound in our daily life. The sound is a type of mechanical wave as it requires a medium for propagation. It travels in all directions. We hear a different kind of sound in our daily life. Sound cannot travel in a vacuum. Flies cannot hear sound at all. Sound travels faster in solid than through air. There is no sound in space as there is no object to travel through or for the propagation of sound. Sound energy is not used for electricity as it produces a very low level of energy. When whales communicate with each other underwater, their sound can travel up to 800km in the ocean.

Sources of sound

Source: www.shrutihearingcare.com Fig: Sound
Source: www.shrutihearingcare.com
Fig: Sound

Sound is produced due to the vibration of a body. Every vibrating object is the sources of sound energy. There are various sources of sound energy like radio, guitar, piano, human beings, animals, etc. We are able to hear the different sound because as the sound (vibrations) enters our ear, the ear (eardrum) also vibrates. The vibration of eardrum transmits a sound impulse to the brain through auditory nerve. Sound propagates in the form of a wave. The speed of sound is 767 miles per hour.

Activity 1
Put your fingers in your throat and speak for some seconds or sing any one of the songs you like. What do you observe ? What do you conclude from this experiment?

Activity 2
Bring a guitar and play one of the strings of the guitar. What do you observe? What do you conclude from this activity?

Wave motion

Sound needs a medium for propagation. It propagates through air, liquid and solid. Sound propagates in the form of waves. A wave is a disturbance that travels through a medium from one location to another location. Wave motion is the transfer of disturbance from one point to another point with no net transport of the material of the medium itself. Simply wave motion means the disturbance in a medium. The motion of the electromagnetic wave, sound wave, etc. are some examples of wave motion. Depending on the direction of vibration, wave motion is of two types which are as follows,

Transverse wave

A transverse wave is a wave in which the particles of the medium move in a direction perpendicular or right angles to the direction of the wave. A ripple on a pond, waves on a string, wave on a rope, etc. are some examples of the transverse wave. Transverse waves cannot propagate in a gas or a liquid because there is no mechanism for driving motion perpendicular to the propagation of the wave. It consists of two parts crests and troughs. Crest is the point of maximum displacement and trough is the point of maximum negative displacement of a transverse wave.

Source: sciencewaveproperties.weebly.com Fig: Longitudinal wave and Transverse wave
Source: sciencewaveproperties.weebly.com
Fig: Longitudinal wave and Transverse wave

Longitudinal wave

A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction of the wave. Soundwave is a common example of the longitudinal wave. Other examples of the longitudinal wave are earthquake wave, tsunami wave, wave produced in slinky. It consists of two parts, compression, and rarefaction. A compression is a region where the particles are closer to each other and rarefaction is a region where furthest apart.

Propagation of sound wave

Sound waves are longitudinal because the direction of vibration of the particles is parallel to the direction of the wave. Sound propagates or travels through solid, liquid and gas. It cannot travel through a vacuum. Sound can propagate through air. The speed of sound is determined by the properties of the air, and not by the frequency or amplitude of the sound. The speed of sound in air is about 332 meter per second. Similarly, it propagates through solid and liquid. The sound wave travels faster in solid than in liquid and gas. The speed of sound in a water medium is about 1498m/s. The speed of sound in steel is 5200m/s.

Speed of sound in different medium

The speed of sound in a different medium is different. Sound travels faster in solid than in liquid and gas. Since the molecules of solid are closely packed the vibrations are transferred easily and fast. The speed of sound is minimum in the air as the molecules of air are loosely packed . The speed of sound in different medium is as follows,

Names of medium Speed of sound
Sea water (at 25 degree celsius) 1533m/s
Glycerol 1904m/s
Mercury 1450m/s
Diamond 12000m/s
Gold 3240m/s
Rubber 1600m/s
Hydrogen (0 degree celsius) 1286m/s

Factors affecting the speed of sound in air

There are various factors which affect the speed of sound. They are given below,

  1. Density
    The speed of sound is inversely proportional to the density of air. When the density of air increases then the speed of sound decreases and vice-versa. The speed of sound in hydrogen is more than the speed of sound in helium as the density of hydrogen is less than the density of helium.
  2. Temperature
    Temperature has a large effect on the speed of sound. Temperature affects the speed of sound because the temperature can affect the “elastic” qualities of different mediums. In the air, the speed of sound increases when the temperature increases and decreases when the temperature decreases. Sound travels faster in hot summer day then in cold winter day.
  3. Humidity
    It is the amount of water vapour present in the air. Humidity decreases the density of air and vice-versa. So, when the humidity of the air increases then the speed of sound decreases and decreases when the humidity of air increases. The speed of sound in moist air is more than that in dry air.
  4. Wind
    The speed of sound is affected by the direction of movement of wind. If the wind is blowing in opposite direction of the sound in which it travels then the speed of sound decreases and vice- versa.



  • Sound is a form of energy which gives the sensation of hearing.
  • Sound is produced due to the vibration of a body. 
  • A transverse wave is a wave in which the particles of the medium move in a direction perpendicular or right angles to the direction of wave.
  • A longitudinal wave is a wave in which particles of the medium move in a direction parallel to the direction of wave.
  •  Sound travels faster in solid than in liquid and gas.
.

Very Short Questions

A sound is a form of energy which gives us the sensation of hearing. Any three sources of sound are as follows,

  • Animals
  • Vehicles
  • Musical instrument

The wave in which the particles of the medium vibrates up and down perpendicular to the direction of the wave is called a transverse wave. Any two examples of the transverse wave are as follows,

  • Ripples produced on the water surface in a pond.
  • Vibration of the stretched wave in musical instrument.

The wave in which the particles of the medium vibrate to- and -fro (back and forth) in the direction of the wave is called longitudinal waves. Any two examples of longitudinal wave are as follows,

  • Soundwave
  • Wave formed on a slinky when pulled and pushed.

The speed of sound in air is 332m/s.
The speed of sound in the water medium is 1498m/s.
The speed of sound in steel medium is 5200m/s.

The wave in which the particles of the medium vibrate to- and- fro (back and forth) in the direction of the wave is called a longitudinal wave. Since, when a sound wave passes through the air, the particle of the air vibrate back and forth parallel to the direction of propagation of the sound wave. It forms a region of compression and rarefaction. So, the sound wave is a longitudinal wave.

The factors that affect the speed of sound in air are as follows,

  • Density
  • Temperature
  • Humidity
  • Wind

Humidity is the amount of water vapour present in the air. The presence of water vapour decreases the density of air. The speed of sound decreases when the density of sound increases. So, the speed of sound increases when the humidity of air increases and vice versa.

The differences between the transverse wave and longitudinal wave are s follows,

Transverse wave Longitudinal wave
The particles of the medium vibrate perpendicular to the direction of propagation of sound. The particles of the medium vibrates parallel to the direction of propagation of sound.
The wave travels in the form of crests and troughs. The wave travels in the form of compression and rarefaction.
This wave can be polarised. This wave cannot be polarised.

Crest is defined as the point of maximum displacement of a transverse wave and troughs is defined as the point of maximum negative displacement of a transverse wave. Crest is also known as peak.

A compression is that part of a longitudinal wave in which the particles of the medium are closer to one another and rarefaction is the part of the waves in which the particles are farther apart.

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  • The form of energy that produces a sensation of hearing is called

    Electricity
    Light
    Heat
    Sound
  • Which one of the following is required to produce sound?

    Vibration of a body
    Gas medium
    Solid medium
    Liquid medium
  • Sound cannot propagate through

    Gas
    Vacuum
    Solid
    Liquid
  • What is the speed of sound in steel?

    5200m/s
    450m/s
    330m/s
    5300 m/s
  • What is the speed of sound in water medium?

    1233m/s
    1023m/s
    1498m/s
    330m/s
  • What is the speed of sound in air?

    238m/s
    328m/s
    350m/s
    332m/s
  • The speed of sound is maximum in

    Water
    Gas
    Liquid
    Solid
  • Which one of the following is not the sources of sound?

    Stone
    Piano
    Guitar
    Radio
  • How many types of waves are there?

    7
    2
    3
    5
  • Sound travels in the form of

    Transverse wave
    Longitudinal wave
    Perpendicular wave
    Vertical wave
  • Which one of the following is the source of sound?

    Magnet
    Bulb
    Guitar
    Tourch
  • The disturbance in a medium is called

    Crest
    Troughs
    Mist
    Wave
  • The maximum negative displacement of a transverse wave is called

    Crest
    Trough
    Wave
    Fro
  • The wave in which the particles of the medium vibrate to- and -fro in the direction of the wave is called

    Transverse wave
    Perpendicular wave
    Vertical wave
    Longitudinal wave
  • The wave in which the particles of the medium vibrate up and down perpendicularto the direction of the wave is called

    Transverse wave
    Perpendicular wave
    Vertical wave
    Longitudinal wave
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