SOUND AND ITS NATURE & PROPAGATION

HOW SOUND IS PRODUCED?

Sound is a form of energy and it is produced by a vibrating body. Whenever a sound is produced, the vibration of the sounding body can be observed or felt.

Experiment: Place a pan upside down on a table and strike it with a spoon. A particular sound will be heard. We can feel its vibrations by touching it with our fingers. We can also see its vibrations by placing small pieces of paper on the pan, which start jumping.

NATURE AND PROPAGATION O F SOUND

Sound waves are Compressional waves. To verify and study the nature and propagation of sound we consider the motion of a vibrating tuning fork. Strike a tuning fork on a rubber pad. The prongs of such a tuning fork begin to vibrate.

When the prongs move right to the equilibrium position, they compress the layer of air in front of it. The compressed layer transfers its increased pressure to the air layer next to it. This process continues and the compression produced by rightward movement of the prong. Now when the prongs move left to the equilibrium position, the pressure in the adjacent layers of air decreases and a rarefaction is produced here. This first layer transfers its decrease in pressure

To the next layer and after doing so it comes to its normal position. As the tuning fork continues to vibrate to and fro against its mean position compressions and rarefactions are produced and travels outwards one after the other. Such a series of compression and rarefactions are the sound waves.

“SOUND CANNOT TRAVEL IN VACUUM”

The apparatus consists of a jar which is placed on the platform of a vacuum pump. As electric bell is suspended in the jar with the help of two wires passing through a cork fixed in its mouth. The electric bell will begin to ring on connecting the free ends of the two wires to a battery. The sound of the bell can be heard. Now start pumping out air from the jar by means of vacuum pump. The sound of the bell starts becoming feeble. At last the sound of the bell becomes hardly audible in spite of the fact that we see the hammer stinking the bell. We can conclude from the experiment that the presence of air is necessary for the propagation of sound.

WHAT IS AUDIBLE FREQUENCY RANGE?

Answer.         Sound is produced by a vibrating body. A simple pendulum also vibrates but it does not produce any sound. The reason is that its vibrations are very slow. And a human ear can hear a sound only if its frequency lies between 20 and 20000 Hz. Sounds of frequency beyond 20000 Hz are inaudible because the eardrum cannot vibrate so rapidly. The audible frequency range differs a little for different persons. Young children can hear sounds of 20000 Hz frequency, but old people cannot hear sounds even above 15000 Hz frequency.

Read More

1. Important Trigonometric Ratios
2. Waves & Its Types
3. What are Physical Quantities?
4. Scientific Method