Science: Sound and Communication: Nature Measure and Quality of Sound (For CBSE, ICSE, IAS, NET, NRA 2022)

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Longitudinal Wave

  • The displacement of the particles and propagation of the wave are in the same direction.
  • The longitudinal waves can form in all the three media viz. solid, liquid and gas.
  • To see a longitudinal wave , take a spring, fix it between two ends and then pull or press it on one end along the length. Compressions and rarefactions can be seen moving and rebounding along the axis of the spring.
Longitudinal Wave

Nature Measure and Quality of Sound

  • Sound level is measured in units of decibel (dB) . For average human ears, the whisper is about 30 decibel. The normal conversation is about 65 decibels while a jet plane taking off makes a noise of about 150 decibel. Beyond 85 decibels, sound is damaging and can lead to temporary loss of hearing.
  • Music is a set of sound that is pleasing to hear and is not random. It refers to the quality of sound as well as the tune. Noise is random and irritates while music has periodicity whether in beats, or rhythm.
  • Sound from a metallic tumbler on hitting with a metallic spoon is higher in pitch than sound from a pitcher when hit with wooden stick.
  • The flute produces a higher pitch because smaller wavelength higher frequency as the relationship between frequency and wavelength .

Use of Different Kinds of Waves in Communication Devices


  • Sonar is a technique that makes use of this property of sound. SONAR stands for Sound Navigations and Ranging. This works on the principle of echo of transmitted sound waves from objects.
  • The advantage of using sonar wave over electromagnetic waves is that electromagnetic waves lose energy fast in the ocean water because water can conduct electricity. In contrast sonar waves can travel farther in water.
  • There can be two types of Sonar set-ups. One is Passive and the other Active.
  • In Passive Sonar, one detects sound waves that are present around
  • Active Sonar has two major components:
    • A transmitter consisting of a signal generator, power amplifier and a transducer.
    • A detector which may be a single detector or an array of several detectors.

If velocity of the sound in water is v, then distance of the object .

where ‘t’ is the time-lapse between transmission and detection of sonic signal.

Sonar is Technique


Radar is an acronym for Radio Detection and Ranging and is useful in many ways to us:

  • Observation of atmospheric objects and phenomena like clouds, cyclones, rain drops etc. and prediction of weather
  • Air Traffic Control
  • Ship navigation
  • In military use (early warning and fighter control radar)

The basic elements of RADAR system are:

  • A pulse source and a transmitter with an aerial which՚d emit radio waves
  • An object which՚s reflect the radio wave
  • A receiver with an antenna and a display system like Cathode Ray Tube (somewhat like a television or a computer monitor)
Radio Detection and Ranging

Different Type of Communication Systems and Devices

  • Microphone and speakers
  • Telephone
  • Satellite, Computer and internet in communication


  • The inventions of microphone, speakers, telephone, satellite, computer and internet and HAM have revolutionized communication. They all work through the conversion of sound wave/text into electromagnetic waves at transmission end and reconversion to sound wave/text at the receiver՚s end.
  • A microphone (mic) converts sound into electrical signal, while the speaker converts it back into sound. Mic can be of different types like condenser, piezoelectric, contact and magnetic mic.
  • Sound pollution can have dangerous implications and hence care should be exercised that the level is kept low. Prolonged use of mobile phone can damage us and there is possibility of serious illness.

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