Among the phenomena characteristic of wave processes is the interference of waves is the fact that the mutual superposition of two waves can be strengthening and weakening of oscillation.
To see this phenomenon, consider what would happen if at some point of the space will be coming waves of the same length.
observe this phenomenon on the example of waves propagating on the surface of the water.We will continuously create waves on its surface in some two points.To this end in the vicinity of the water surface will place the ends of two wires, fastened to a resilient metal plate.At the ends of the wires swing plate will be periodically immersed in water, and excite vibrations propagate as waves of equal length on its surface.Each of the delay wave excites your system.Two wave systems, superimposed on one another, interact, and thus will be interference waves.
important that the two wave systems have been agreed, t. E. To the same length they came out of the centers of oscillation in the same phase, or if they are when an out of phase (e.g., occurred in opposite phases), then the shiftphase-in time should not be changed.Such waves are called coherent.In this experiment, the coherence achieved in that both ends of the wire are periodically simultaneously touch the surface of the water - wave leaves the center oscillation in the same phase.
construct a picture of the two systems of coherent superposition of waves.The solid circles denote ridges ring waves propagating along the surface of the water from the springs, and a dotted line - depression.The points where there are waves of both systems in the same phase, with depression and depression with a ridge crest - point reinforced fluctuations (highs).Points also weakened fluctuations (minimum), located in the place where the trough of one wave crest to the other.If you have a picture of the coherence of waves of alternating highs and lows will be stable.In fact, if you are currently at a point there, comb with a comb, then a half-period in the same meet with a hollow cavity, and after half a period again comb with a comb, etc., ie,at this point all the time will be a maximum oscillation.Such a change of minima and maxima of the oscillation amplitudes is called an interference pattern.And the phenomenon of superposition of waves, forming an interference pattern called interference waves.
To address the issue of public phases meet at a given point of interfering waves, it is necessary to take into account the difference in their turn.It is enough to count the number of waves of an appropriate system that fit in the distance between the point of interest of highs and lows and the centers of oscillation.We will see that the maxima are in the points, which are either located at equal distances from both centers, or at points where the path difference corresponds to an even number of half wavelengths, while at least - an odd number.
an example of this experience, we have considered the phenomenon of interference of mechanical waves.
However, the interference phenomenon is not unique to waves generated on the surface of the water, but also all types of waves, acoustic, electromagnetic and others.Therefore, if the light has wave properties, then the imposition of his two beams occurs interference of light waves.
sources emitting such waves are called coherent.In optics, coherent sources can only be created artificially.
We should not forget that the interference waves (all, including light) occurs only when the waves that interact have the same frequency and time-dependent phase shift at any point.
