SOUND

In the study of sound, we learn about the source, the medium and the receiver. Sound energy is transmitted from the source to the receiver via the medium. An example of the source is a tuning fork. It provides sound of a single frequency f. If the arms of the tuning fork vibrate 261 times in a second, we say its frequency of vibration is 261 Hz and the produced sound (vibration of the molecules in air, the medium) has the same frequency. As the arms of the tuning fork vibrate, a series of high (compression) and low (rarefaction) pressure regions in the air (the medium) is generated and propagates outwards. This series of compressions and rarefactions constitutes a traveling sound wave in the air. 

SOUND WAVE IN TERMS OF AIR PRESSURE VARIATION: -

Air pressure p (Nm^-2) at a particular time. The last graph shows the pressure variation of the medium (air) versus distance in front of the source at a particular time. 

The distance from one compression (or rarefaction) to the next is called a wavelength l.

 It is a traveling wave. The pattern moves away from the source as time progresses. 

              ∆ p at a latter time another way to describe the sound wave is to stand at a particular position (e.g. position Q) in front of the source and record the pressure variation as a function of time t.

 ∆ p at a particular position. The interval from one high (or low) to the next is called the period T of the sound wave.

 The relationship between f and T is F = 1 / T.