Important Points of Sound | Class IX

  • Sound is a mechanical energy which produces sensation of hearing. Sound is produced due to vibration of different objects.
  • Sound wave propagates as compressions & rarefactions in the medium. Sound waves are longitudinal waves.
Characteristics of a Sound Wave
      Sound waves are produced due to variations in pressure & density of the        medium.
   Compression is the portion of the medium where a temporary increase in volume & a decrease in density takes place when a sound wave passes through the medium.
   Rarefaction is the portion of the medium where a temporary increase in volume & consequently a decease in density takes place when sound wave passes through the medium.
   Crest is the portion of the medium where the density (or pressure) has a value larger than its average value.
   Trough is the portion of the medium where the density (or pressure) has a value smaller than the average value.
   Amplitude is the magnitude of the maximum disturbance in the medium on either side of the mean position.
   Oscillation is the change in density (or pressure) from maximum value to the minimum value and again to the maximum value.
   Frequency enables us to know as to how many times a particular event occur in a given time.
   Time Period is the time taken for one complete oscillation in density (or pressure) of the medium.
   Wavelength is the distance between two consecutive compressions or two consecutive rarefactions.
      Characteristics of Sound
   Loudness or intensity.
   Pitch or frequency.
   Quality or timbre.
      Reflection of Sound
   An Echo is the phenomenon of repetition of sound of a source by reflection from an obstacle.
   Multiple echoes are heard when sound is repeatedly reflected from a number of obstacles at suitable distance.
   Megaphone, stethoscope ear trumpet, hearing aid etc are based on phenomenon of multiple reflection of sound.
   Reverberation is the phenomenon of persistence of audible sound after the source has stopped emitting sound.
      Reverberation is reduced by carpeting the floor, upholstering furniture & covering the walls with some absorbing material like curtains etc.
      Range of Frequencies
   Audible range of hearing of average human being is in the frequency range of 20Hz to 20KHz.
   Infrasound has a frequency below 20Hz. Ultrasound has a frequency above 20 kHz.
   Ultrasound finds application in industry, medical service & communications.
      Human Ear
   Outer ear collects sound waves.
   Middle ear amplifies the sound waves.
   Inner ear converts the amplified sound energy into electrical energy & conveys to the brain as nerve impulse for interpretation.

 

Advertisements

Leave a Reply

Your email address will not be published. Required fields are marked *