SOUND        CLICK HERE SOUND-  The form of energy which causes the sensation of hearing in our ears. LIMITS:- 1.The Range of Sound from 20Hz to 20000 Hz is called the range  of  audibility. 2.The sound frequency  above 20000Hz is called ultrasonic waves/sound. 3.The sound frequency below 20Hz is called infrasonic sound/waves. 4.Sound can't travel in vacuum  (place without air). POINTS TO REMEMBER :- *Amplitude:- The maximum displacement of the particle of a body on either side of its mean position. *Time Period :- The time taken by the particle of the medium to complete it's one vibration. *Wavelenght:- The distance travelled by wave in one time period.  *Frequency :- The no. of vibration made in one second. *Wave Velocity :-  The distance travelled by wave in 1 second.