Sound

Sound

Sound:-
 Sound is a form of energy which emitted by a vibrating body that travels in the form of waves and causes the sensation of hearing sound cannot travel through vacuum.
 The mechanical wave energy which can be heard by human ear is known as sound.
 Sound is propagate in the form of longitudinal mechanical waves.
 A material medium is necessary for the propagation of sound.
 Medium must posses elasticity and inertia velocity of sound in air at STP is 330m/s.
 Velocity of sound depends on nature of the medium and temperature of the medium.
 If a sound wave travelling from one medium to another medium its velocity wave length change but its frequency remains constant.
 Sounds of all frequencies are not audible.audible sound frequency is 20Hz to 20,000Hz.
 Sound waves of frequencies less than  20 Hz are known as infrasonic.
 Sound waves of frequencies grater than 20000Hz  are known as ultrasonics.
 Velocity of sound is maximum in solids intermediate in liquids and minimum is gases.

Types of Waves:
 1.Mechanical Waves
 2.Electro Magnetic Waves        
Sound is a mechanical wave. 
 

Mechanical Wave : The wave which needs a material medium (solid, liquid or gas) for its propagation is called Mechanical Wave or Elastic wave. Mechanical Wave cannot travel through vacuum.

Types of Mechanical Waves: 
There are two distinct types of mechanical waves.
1.Longitudinal Waves.
2.Transverse Waves

1. Longitudinal Waves :
The waves produced by particles vibrating parallel to the direction of propagation of the waves are called Longitudinal waves.


Consider a long spring fixed to one end on a table. If a gentle push is given to the free end of the spring and released, the spring oscillates laterally which is parallel to the wave propagation. Apart form this, a few rings of the spring during vibrations have less distance between certain adjacent rings then before the disturbance started. These regions are called compressions (C). Alternatively at certain movement there are some regions in the spring where the distance between two adjacent rings is larger than their actual distance of existence. These regions are called rarefactions (R). Hence a longitudinal wave propagates in a medium in the form of compressions and rarefactions.

2.Transverse Waves :
The waves produced by particles vibrating perpendicular to the direction of propagation of the waves are called transverse waves.Consider a rope to a fixed support, hold the free end of the rope stretch and vibrate in a perpendicular direction to the length of the string. A wave as shown in figure can be set up.


The wave propagates because of vibration of particles of the string up and down. At a certain movement of time the vibrating particles have maximum displacement in the upward direction from the mean position known as crest. At the same movement the vibrating particles have maximum displacement in the down ward direction from the mean position known as trough. Hence a transverse wave propagates in a medium in the form crests and troughs.