G10 Sound Waves and Speed of Sound PDF

**7.6 SOUND WAVE AND SPEED OF SOUND** **Sound Wave** Sound is a form of energy that is transferred from one place to another in a certain medium. Sound wave is produced by a vibrating object placed in a medium. The pressure changes occur alternately in the medium by vibrating object. The medium is...

**7.6 SOUND WAVE AND SPEED OF SOUND** **Sound Wave** Sound is a form of energy that is transferred from one place to another in a certain medium. Sound wave is produced by a vibrating object placed in a medium. The pressure changes occur alternately in the medium by vibrating object. The medium is usually air, but it can be any gas, liquid (or) solid. Sound wave propagates as a series of compression and rarefaction like longitudinal waves on a vibrating spring. Like other waves, sound wave can be reflected and diffracted. Unlike electromagnetic waves, sound waves need a medium to propagate. Sound wave cannot travel through vacuum. The compression is created in the medium as the vibrating object moves forward, since it pushes molecules together. The compression region has higher pressure. When the object moves back, the molecules are spread out and rarefaction is created and the pressure of that region is low. After the object is vibrated several times, it has created a series of compression and rarefactions travelling away from the vibrating object. The pressure of the medium is changed into higher and lower alternately. In this way, sound energy propagates through the medium to the ear. When waves enter the ear, they strike the ear drum and make it vibrate. This vibration of ear drum results the hearing of the sound. Sound energy is transferred through the medium by the successive pressure changes among the adjacent parts without moving the medium as a whole. vibrating speaker cone loudspeaker air pressure is high air pressure is low vibrating diaphragm compression rarefaction high low distance Grade 10 ce it bject that Occur any like and SSION mis *the* This ough g the Wavelength Wavelength Figure 7.21 Pressure-distance graph of a propagated sound waves Audible range: The average person can only hear sound that has a frequency higher than 20 Hz and lower than 20 000 Hz. This interval of frequency is called the audible range (or) hearing range. But the range becomes reduced according to age and health conditions. Sound waves with frequencies greater than 20 000 Hz are called ultrasounds. Some objects vibrating with frequencies under 20 Hz produces sound which cannot be heard by human. This is called infrasound. It is found that, by experiments: dog, bat and dolphin can hear the ultrasound and they communicate with it. On the other hand, elephants can communicate with infrasound. Speed of Sound Since sound propagates from one place to another through a distance in a time interval in a given medium, the speed of sound is speed of sound = d V= t distance travelled by sound time taken However, sound waves travels at different speeds in different media through which it passes. Generally, the speed of sound depends on the density of the medium. The denser the medium is, the greater the speed because the particles of the medium are tightly bound together. This means that the disturbance can be transferred more quickly from one particle to next. Table 7.1 The speed of sound in some solids, liquids and gases **Speed** Medium m s ft s **Temperature °C** Air 332 1090 0 CO2 259 850 0 Cl 206 676 0 Water, pure 1 404 4 605 0 Copper 3.560 11 680 20 Iron 5130 16 830 20 75