Characteristics of a sound wave


  • Sound wave is longitudinal wave consisting of compression and rarefaction traveling through a medium
  • To describe a sound wave we need to know five terms
  • Time Period,Frequency,Wavelength,Amplitude,and Velocity



In the Above Image

  • Sound Wave ABCDE and EFGHI .
  • It starts from position A (normal density position) and compress along ABC and Rarefaction along CDE
  • Again it returns to its normal position E
  • Thus The ABCDE portion shows a complete Wave



  • The Minimum Distance in which a sound wave repeats itself is called its wavelength
  • It is denoted by the symbol  lambda  λ
  • The Combined length of one compression and rare fraction is called its wavelength
  • In the above figure the combined length of AC and CE means the length ACE is the wavelength
  • The SI unit of wavelength is Meter



  • When a wave passes through a medium ,the particles of the medium gets displaced temporarily from their original position
  • In the Figure PB is the Amplitude
  • The maximum displacement of the particle of the medium from their original undisturbed position is called amplitude
  • The SI unit of Amplitude is Meter


Time Period

  • The Time required to produce one complete wave is called time period
  • You can say the time taken to travel from Point A to point E is the time period
  • The Unit of time period is Second


  • The Number of complete cycles produced in one second is called Frequency
  • The Unit of frequency is Hertz Hz.

Also F= 1/t

Where Frequency = 1/ Time Period

Velocity Of Wave(Speed of wave)

  • The distance traveled by a wave in one second is called its velocity.
  • Its unit is M/S


The Relationship between frequency wavelength and velocity



  1. If 25 sound waves are produced per second,what is the frequency in hertz.

Ans. As the name Says Frequency is equal to number of waves produced in a second .hence frequncy is equal to 25 hertz.


Now Another Problem

2.The Wavelength of  a sound emitted by a source is 1.7 × 10 -2 m. calculate the Frequency of the sound if its velocity is 343.4 m/s .


The Relationship between frequency wavelength and velocity is given by

v= f ×λ

v= velocity of the wave


λ= Wavelength

Velocity of the wave = Frequency × Wavelength

So     343.4 = f ×  1.7 × 10 -2 m

f = 2.02 ×  104 Hz.

Here is the link to download NCERT solutions For Class 9th

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