Physics XII Notes for Physics Notes

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Wave and Wave Motion

The change in pressure density or displacement of particles of the medium about their equilibrium position is disturbance for Eg: When a stone is dropped at the center of the pond, the equilibrium of the water surface of the pond is disturbed. Rise and fall of the water surface is observed which is called disturbance.

A wave is a disturbance from an equilibrium condition that propagates or travels with finite velocity from one region of space to another region of space. It is due to the repeated or periodic harmonic motion of particles of the medium about their equilibrium position. Which is called mean position for eg:- The periodic disturbance that travels through the surface of water is water wave.

According to the ways of energy transferring waves are divided into two kinds.

1. Mechanical wave: The wave which need material medium for their propagation are mechanical wave. For eg: the sound waves are mechanical wave and hence need a material medium for propagation.

2. Electromagnetic wave: The waves which do not need material medium for their propagation are called electromagnetic waves. For eg: Light waves are electromagnetic waves and hence do not need material medium for propagation or propagates even in vacuum. The electromagnetic are caused to propagate by two electromagnetic forces.

Wave Motion
The wave motion is disturbance caused in a medium by the repeated periodic motion of the particles of the medium the wave motion possess the following characteristics.
When wave travels forward, the particles of the medium vibrates about their mean position.
Each particles in a medium start vibrating a little later then the preceding one.
The wave velocity is different from the particle velocity the wave velocity is given by,


The wave travels with uniform velocity but the velocity of the particle differ from position to position since it is function of time.

Transverse and longitudinal wave
According to the modes of vibration of the particles, in the medium, there are two types of the wave.

Transverse wave: The wave in which medium particle vibrate perpendicularly to the direction of the propagation of wave is called transverse wave. In the transverse wave the medium particle or disturbance travels in the form of crest and trough. Water wave, light waves are example of transverse wave.
Longitudinal wave: The wave in which medium particles vibration along the direction of propagation of wave is called longitudinal wave the compressional wave in the spring, sound waves etc. are the example of longitudinal wave.
The longitudinal wave travels in the form compression and rarefaction.

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