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Sunday, January 24, 2010

Wave


   A wave is a disturbance that propagates through space and time, usually with transference of energy. A mechanical wave is a wave that propagates or travels through a medium due to the restoring forces it produces upon deformation. There also exist waves capable of traveling through a vacuum, including electromagnetic radiation and probably gravitational radiation. Waves travel and transfer energy from one point to another, often with no permanent displacement of the particles of the medium (that is, with little or no associated mass transport); they consist instead of oscillations or vibrations around almost fixed locations.

Definition


Agreeing on a single, all-encompassing definition for the term wave is non trivial. A vibration can be defined as a back-and-forth motion around a reference value. However, a vibration is not necessarily a wave. Defining the necessary and sufficient characteristics that qualify a phenomenon to be called a wave is, at least, flexible.
The term is often understood intuitively as the transport of disturbances in space, not associated with motion of the medium occupying this space as a whole. In a wave, the energy of a vibration is moving away from the source in the form of a disturbance within the surrounding medium. However, this notion is problematic for a standing wave (for example, a wave on a string), where energy is moving in both directions equally, or for electromagnetic / light waves in a vacuum, where the concept of medium does not apply. There are water waves in the ocean; light waves from the sun; microwaves inside the microwave oven; radio waves transmitted to the radio; and sound waves from the radio, telephone, and voices.


Characteristics


Periodic waves are characterized by crests (highs) and troughs (lows), and may usually be categorized as either longitudinal or transverse. Transverse waves are those with vibrations perpendicular to the direction of the propagation of the wave; examples include waves on a string, and electromagnetic waves. Longitudinal waves are those with vibrations parallel to the direction of the propagation of the wave; examples include most sound waves.
When an object bobs up and down on a ripple in a pond, it experiences an orbital trajectory because ripples are not simple transverse sinusoidal waves.

Ripples on the surface of a pond are actually a combination of transverse and longitudinal waves; therefore, the points on the surface follow orbital paths.
All waves have common behavior under a number of standard situations. All waves can experience the following:
  • Reflection — change in wave direction after it strikes a reflective surface, causing the angle the wave makes with the reflective surface in relation to a normal line to the surface to equal the angle the reflected wave makes with the same normal line
  • Refraction — change in wave direction because of a change in the wave's speed from entering a new medium
  • Diffraction — bending of waves as they interact with obstacles in their path, which is more pronounced for wavelengths on the order of the diffracting object size
  • Interference — superposition of two waves that come into contact with each other (collide)
  • Dispersion — wave splitting up by frequency
  • Rectilinear propagation — the movement of light waves in a straight line also helpful for seismographs



Polarization

A wave is polarized if it oscillates in one direction or plane. A wave can be polarized by the use of a polarizing filter. The polarization of a transverse wave describes the direction of oscillation in the plane perpendicular to the direction of travel.
Longitudinal waves such as sound waves do not exhibit polarization. For these waves the direction of oscillation is along the direction of travel.this is very important

Examples of Wave
  • Ocean surface waves, which are perturbations that propagate through water
  • Radio waves, microwaves, infrared rays, visible light, ultraviolet rays, x-rays, and gamma rays, which make up electromagnetic radiation; can be propagated without a medium, through vacuum; and travel at 299 792 458 m/s in a vacuum
  • Sound — a mechanical wave that propagates through gases, liquids, solids and plasmas
  • Waves of traffics, that is, propagation of different densities of motor vehicles, and so forth, which can be modeled as kinematic waves, as first presented by Sir M.J. Lighthill
  • Seismic waves in earthquakes, of which there are three types, called S, P, and L
  • Gravitational waves, which are nonlinear fluctuations in the curvature of spacetime predicted by general relativity, but which have yet to be observed empirically
  • Inertial waves, which occur in rotating fluids and are restored by the Coriolis effect



Source:  Wikipedia

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