- Books Name
- Science Made Easy Science Book
- Science Made Easy
- CBSE Class 9
Characteristics of Sound Wave
• The characteristics of sound waves are : wavelength, frequency, amplitude, time period and
→ When a wave travel in air the density and pressure of air changes from their mean position.
→ Compression is shown by crest while rarefaction is shown by trough.
→ Compression is the region of maximum density or pressure.
→ Rarefaction is the region of minimum density or pressure.
→ In sound waves the combined length of a compression and an adjacent rarefaction is called
→ The distance between the centres of two consecutive compressions or two consecutive
rarefactions is also called its wavelength.
→ It is denoted by the Greek letter lamda (λ). Its SI unit is metre.
→ No. of complete waves produced in one second or number of vibrations per second is called
→ Number of compressions or rarefactions passed in one second is also frequency.
→ Frequency of wave is same as the frequency of the vibrating body which produces the wave
• The SI unit of frequency is hertz (Hz). The symbol of frequency is v (nu).
• 1 Hertz: One Hz is equal to 1 vibration per second.
• Bigger unit of frequency is kilohertz kHz = 1000 Hz.
→ Time taken to complete one vibration is called time period.
→ Time required to pass two consecutive compressions or rarefactions through a point is called
• SI unit of time period is second (s). Time period is denoted by T.
• The frequency of a wave is the reciprocal of the time period.
• v = 1/T
→ The maximum displacement of the particle of the medium from their original undisturbed
position is called amplitude of the wave.
• Amplitude is denoted by A and its SI unit is metre (m).
→ Sound have characteristics like pitch and loudness and timbre.
• Pitch: The pitch of sound depends on the frequency of sound (vibration).
→ It is directly proportional to its frequency. Greater the frequency, higher is the pitch and lesser the
frequency, lower is the pitch.
→ A woman’s voice is shrill having a high pitch while a man’s voice is flat having low pitch.
• Loudness: The loudness depends on the amplitude of the sound wave.
→ Loudness is the measure of the sound energy reaching the ear per sec.
→ Greater the amplitude of sound wave, greater is the energy, louder the sound; short is the
amplitude, less is the energy, soft is the sound.
→ Loudness is measured in decibel ‘dB’.
• Quality or Timbre: The timbre of a sound depends on the shape of sound wave produced by
the characteristic of musical sound.
→ It helps us to distinguish between two sounds of same pitch & loudness.
• Sound of single (same) frequency is called tone while a mixture of different frequencies is called
• The distance travelled by a wave in one second is called velocity of the wave.
• Its SI unit is metre per second (m/s ).
Velocity = Distance travelled/Time taken
⇒ v = λ/T
(λ is the wavelength of the waves travelled in one time time period T)
v = λv (1/T = v)
So, Velocity = Wavelength × Frequency
This is the wave equation.
Example: What is the frequency of sound wave whose time period is 0.05 second ?
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