Science: Sound and Communication: Characteristics and Nature of the Wave (For CBSE, ICSE, IAS, NET, NRA 2022)

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Characteristics and Nature of the Wave

Sound is a result of vibration. The vibration is produced by a source, travels in the medium as a wave and is ultimately sensed through the ear – drum.

  • Sound has an association with vibrations -These vibrations are transmitted in a medium mechanically. It travels like a wave.
  • A medium is a must for mechanical waves like sound to travel- sound needs a medium to travel. In contrast, we can receive electromagnetic waves from distant stars and artificial satellites in space as electromagnetic waves need no medium to travel.
  • A wave involves a periodic motion, movement that repeats itself-It also transports energy.
  • Crest and trough are essential components of a wave. A wave transfers energy from one point to the other without the medium particles moving from one point to the other. Thus, wave is clearly different from particle.

Representing a Wave

Representing a Wave


The maximum height of the wave.


The distance between adjacent troughs or adjacent crests, measured in unit of length such as meters and expressed by symbol λ (lambda) . For longitudinal wave, it will be distance between two successive rarefactions or compressions.

Time Period

This defines the time it takes for one complete wave to pass a given point, measured in seconds (s) .


The number of complete waves that pass a point in one second, measured in Hertz (Hz) .

Speed or Velocity

Wave speed is defined as the distance travelled by a wave disturbance in one second and is measured in meters/second (ms – 1) . Speed is scalar quantity while velocity is a vector quantity.

Velocity = frequency × wavelength


Movement of Sound Waves in Air

  • Sound waves travel in fluids and solids as longitudinal waves.
  • A longitudinal wave is a wave in which vibration, or the displacement takes place in the direction of the propagation of the wave. Sound moves due to difference in pressure.
  • If there is no medium, then produced sound will not be able to push any medium-molecules and sound will not move.

Different Types of Waves

The waves can be of different types. These may be mechanical or electromagnetic.

Mechanical Wave

  • Mechanical wave are those waves that require a medium for travelling.
  • Their speed is dependent on the properties of the medium such as inertial and elastic properties.
  • The speed of the wave will depend on how easy or difficult is it to displace the particles of the medium (that is to say on their inertia) and on how those particles regain their original positions which is the elasticity.

Electromagnetic Wave

  • Electromagnetic wave results from acceleration of charge.
  • It doesn՚t require a medium to travel. It can travel through vacuum such as light do waves which travel from stars through empty space to reach us.
  • The electromagnetic wave has electric and magnetic fields associated with it.
  • The 2 fields, electric and magnetic, are perpendicular to each other and also to the direction of propagation.
  • When we mention the wavelength of an electromagnetic wave, we don՚t mean any physical separation between any crests or troughs or between rarefactions and compressions. This is because sound wave creates low- and high-pressure points in traveling through, say, air.

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