The word wave brings to our mind a picture of water waves moving across the pond of water. When a stone is dropped in a still pond of water, a disturbance is produced at that point and circular ripples will be formed which travel out and finally reach the shore of the pond. If we float a cork at a suitable place in the pond, it will simply move up and down without any forward or backward movement. This shows that it is not the water that moves outward, but it is the wave (i.e. disturbance) that travels outward. So a wave consists of oscillations that move without carrying matter with them. A wave, in general, is a disturbance that travels from one region to another region in a medium. The wave carries energies without transport of matter.
There are two ways of energy transfer by waves. The waves which require material medium for their transmission are called mechanical waves. Sound waves, ripples on a pond, vibration in a stretched string are some examples of mechanical waves. These are also called the elastic waves. On the other hand, the waves which do not require material medium for their transmission are called non-mechanical waves. Electromagnetic waves such as X-rays, light waves, microwaves, radio waves are some examples of non-mechanical waves. The electromagnetic waves can be transmitted through vacuum.
1. Wave
A wave is a continuous transfer of disturbance from one part of a medium to another through successive vibrations of the particles of the medium about their mean positions. In a wave motion, energy and momentum are carried from one region to another region of the medium. If there is no transfer of energy, it is not a wave but an oscillation. In order to produce a mechanical wave, we need a source which produces disturbance and an elastic medium. When a particle of the medium is disturbed by some source, it begins to vibrate about its mean position. The disturbance of this particle is transferred to the next particle due to the elastic property of the medium. The second particle also starts to vibrate about the mean position and transfers the disturbance to the third particle and so on. In this way, disturbance, i.e. wave, is transmitted from particle to particle. In wave motion, the disturbance travels through the matter, but the particles of the medium do not move themselves along with the disturbance.
The disturbance may be produced in the medium due to change in pressure or change in density, etc. For transmission of energy through the medium, the medium should possess the elasticity behavior and inertia, it can store energy. It is assumed that the frictional forces are not very large, otherwise the wave motion will die out very soon. Thus wave motion is a form of disturbance which travels through a medium due to the repeated periodic motion of the particles of the medium about their mean positions, the disturbance being handed from one particle to the other.
Some Important Terms
Crest: The maximum displacement of the particles of a medium above the equilibrium position is called a crest.
Trough: The maximum displacement of the medium particles below its equilibrium position is called a trough.
Amplitude: The maximum displacement of a particle from its equilibrium state when a mechanical wave passes through the medium is called the amplitude.
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