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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 sound 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

               1.  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.
               2.  Infrasonic sounds
                   Sounds of frequencies less than 20 Hz are called infrasonic sounds. They are
               inaudible.
               3.  Ultrasonic sounds
               The sounds of frequencies greater than 20,000 Hz are called ultrasonic sounds. They
               are inaudible.
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