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SAI INTERNATIONAL SCHOOL
                                                          Class8
                                                     Lesson Notes
                                                   Subject-Physics
                                                       CH-Sound
                                       Subtopic-Characteristics of sound


               Characteristics of sound:
               1. Loudness:
                       The sensitivity of our ears to sound is called loudness. The loudness of sound
               depends on its amplitude. The loudness of sound is proportional to the square of the
               amplitude. A roar of a lion is louder than a woman’s voice. The loudness of sound is
               measured in Decibel (db). If loudness exceeds 80 db, then the sound becomes
               physically painful.

               2. Pitch:
                       It is the characteristic of sound that differentiates between two sounds of same
               loudness. The pitch of sound depends on its frequency. If frequency is more, then the
               pitch or shrillness is more. The pitch of a woman’s voice is more and it is shriller than a
               man’s voice.


               3. Quality/Timbre:
                       It is the characteristic of sound that differentiates between two sounds of same
               loudness and pitch. Quality of sound depends on waveform.


               Audible and inaudible sound

               Audible sound: Not all sound produced by vibrating bodies is audible. The human ear
               can recognize the sounds of frequencies in the range of 20 Hz to 20,000 Hz. This range
               of frequency of sound is called audible sound.


                   Some animals like dogs and snakes can hear sounds of frequencies greater than
                   20,000 Hz.


               Infrasonic sounds:
                   Sounds of frequency less than 20 Hz are called infrasonic sounds. They are
               inaudible.


               Ultrasonic sounds:
               The sounds of frequency greater than 20,000 Hz are called ultrasonic sounds. They are
               inaudible.
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