WAVE

WAVE (WAVE-3 TV) is a local National Broadcasting Company station in Louisville, Kentucky, USA. It is owned by The Liberty Corporation, and broadcasts from their main studio in downtown Louisville. Its transmitter is located in Oldham County, Kentucky. Television stations in Kentucky NBC network affiliates Louisville media

Wave

:''This article is about waves in the most general scientific sense; a separate article focuses on Ocean surface wave. For other meanings see Wave (disambiguation).'' A wave is a disturbance that propagates, carrying energy. Apart from electromagnetic radiation, and probably gravitational radiation, which can travel through vacuum, waves exist in a medium (bearer) (which on deformation is capable of producing elastic restoring forces) through which they travel and can transfer energy from one place to another without any of the particles of the medium being displaced permanently; i.e. there is no associated mass transport. Instead, any particular point oscillation around a fixed position. Waves are characterised by crests (highs) and troughs (lows), either literally (in the case of transverse waves) or in a graph of particles per cm against time (in the case of longitudinal waves). ==The medium which carries a wave== A medium that can carry a wave is classified by one or more of the following properties: *A ''linear medium'' if the amplitudes of different waves at any particular point in the medium can be added. *A ''bounded medium'' if it is finite in extent, otherwise ''unbounded''. *A ''uniform medium'' if its physical properties are unchanged at different locations in space. *An ''isotropic medium'' if its physical properties are the ''same'' in different directions. == Examples of waves == * Ocean surface waves, which are perturbations that propagate through water (see also surfing and tsunami). * Visible light, radio waves, x-rays, etc. make up electromagnetic radiation. In this case propagation is possible without a medium, through vacuum. These electromagnetic waves travel at about 300,000 km/s. * Sound - a mechanical wave that propagates through air, liquid or solids, and is of a frequency detected by the ear. Similar are seismic waves in earthquakes, of which there are the S, P and L kinds. * Gravitational waves, which are fluctuations in the gravitational field predicted by General relativity. These waves are nonlinear. == Characteristic properties == All waves have common behaviour under a number of standard situations. All waves can experience the following: *Reflection – the change of direction of waves, due to hitting a reflective surface. *Refraction – the change of direction of a wave due to them entering a new medium. *Diffraction – the spreading out of waves, for example when they travel through a small slit. *Interference – the addition of two waves that come in to contact with each other. *Dispersion (optics) – the splitting up of waves by frequency. *Rectilinear propagation – the movement of waves in straight lines. == Transverse and longitudinal waves == Transverse waves are those with vibrations perpendicular to the wave's direction of travel; examples include waves on a string and electromagnetic waves. Longitudinal waves are those with vibrations along the wave's direction of travel; examples include sound waves. ripple tanks on the surface of a pond are actually a combination of transverse and longitudinal waves; therefore, the points on the surface follow elliptical paths. === Polarization === Transverse waves can be polarization. Unpolarised waves can oscillate in any direction in the plane perpendicular to the direction of travel, while polarized waves oscillate in only one direction perpendicular to the line of travel. == Physical description of a wave == Waves can be described using a number of standard variables including: frequency, wavelength, amplitude and period. The amplitude of a wave is the measure of the magnitude of the maximum disturbance in the medium during one wave cycle, and is measured in units depending on the type of wave. For examples, waves on a string have an amplitude expressed as a distance (meters), sound waves as pressure (pascals) and electromagnetic waves as the amplitude of the electric field (volts/meter). The amplitude may be constant (in which case the wave is a ''c.w.'' or ''continuous wave'') or may vary with time and/or position. The form of the variation of amplitude is called the ''envelope'' of the wave. The period (''T'') is the time for one complete cycle for an oscillation of a wave. The frequency (''F'') is how many periods per unit time (for example one second) and is measured in hertz. These are related by: :

f=\frac{1}{T}

. When waves are expressed mathematically, the ''angular frequency'' (''ω'', radians/second) is often used; it is related to the frequency ''f'' by: :

f=\frac{\omega}{2 \pi}

. === Travelling waves === Waves that remain in one place are called ''standing waves'' - e.g. vibrations on a violin string. Waves that are moving are called ''travelling waves'', and have a disturbance that varies both with time ''t'' and distance ''z''. This can be expressed mathematically as: :

y=A(z,t) \cos (\omega t - kz + \phi),\,

where ''A''(''z'', ''t'') is the amplitude envelope of the wave, ''k'' is the ''wave number'' and φ is the ''phase (waves)''. The velocity ''v'' of this wave is given by: :

v=\frac{\omega}{k}= \lambda f,

where ''λ'' is the ''wavelength'' of the wave. === The wave equation === The wave equation is a differential equation which describes a harmonic wave passing through a medium, discussed above. The equation has different forms depending on how the wave is transmitted, and on what medium. Not all waves are sinusoidal. One example of a non-sinusoidal wave is a pulse that travels down a rope resting on the ground, extending in direction ''x'', travelling at velocity ''c''. The height of the pulse above the ground is φ. The distance the pulse travels between some time ''t'' and time 0 is ''ct''. In one dimension the wave equation has the form :

\frac{1}{c^2}\frac{\partial^2\phi}{\partial t^2}=\frac{\partial^2\phi}{\partial x^2}.

A general solution, given by d'Alembert is :

\phi(x,t)=F(x-ct)+E(x+ct).

F and E can be considered to be the shapes of two pulses travelling down the rope, one in the ''+x'' direction, and one in the ''-x'' direction. If we substitute for ''x'' above, instead directions ''x'', ''y'', ''z'', we then can describe a wave propagating in three dimensions. A non-linear wave-equation can cause mass transport. The Schr�dinger equation describes the wave-like behaviour of particles in quantum mechanics. Solutions of this equation are wave functions which can be used to describe the probability density of a particle. ==See also== * List of wave topics * Capillary waves * Demonstrating sound waves on an oscilloscope * Doppler effect * Group velocity * Phase velocity * Ripple tank * Standing wave * Audience wave * Ocean surface wave * Waving Partial differential equations Waves nds:Bülg simple:Wave vi:Chuyển động s�ng

Wave

I think λ should be explained with a link to :wavelength. Also ''I'' is not explained. The article should start with a definition, not with period and frequency. The angular frequency formula is correct. --AxelBoldt --- Reorganized concentrating on simpler topics first. Come on... don't formula look better in another font: like this? --:sodium Hmm. Sorry, didn't check this page before, I just changed it back. With my browser/settings, formulae look much better like this: :''v'' = ω / ''k'' = λ''f'' , than like this: ''v'' = ω / ''k'' = λ''f'' . But that's just for me. Feel free to change it back. -- DrBob ------------------------------------------------------- Examples of waves Sea-waves, which are perturbations that propagate through water (see also surfing and tsunami). Sound - a mechanical wave that propagates through air, liquid or solids, and is of a frequency detected by the auditory system. Similar are seismic waves in earthquakes, of which there are the S, P and L kinds. Light, radio waves, x-rays, etc. make up electromagnetic radiation. Propagating here is 'a disturbance of the electromagnetic field. ' does it want to mean that before "pass a light wave" there is a quiet magnetic field? :I agree that is was oddly formulated. I changed it. - User:Patrick 15:23 Feb 18, 2003 (UTC) ----------- Perfect, but now i think there is another little incongruence. The first paragraph say about waves: "Waves have a medium through which they travel and can transfer energy from one place to another without any of the particles of the medium being displaced permanently". Is not correct to say that for all the kind of waves and to say a few lines later that electromanetic waves don't need a medium... PS: I would correct it myself but my englis is very bad. (Sorry by the lot of mistakes that is sure I have wroten in this short comment). :I was not quite happy with this incongruence either; I have put the exception higher up. May be you can improve it further. Do not worry too much about the English, that can be corrected. - User:Patrick 22:54 Feb 18, 2003 (UTC) ---- It's confusing that "x" is used in the picture to refer to the amplitude. There is an equation down below where "y" is used. --User:Dgrant :I've changed the image. If it is generally agreed that this new one is better, someone should go to the image discription page and delete the old one. User:Theresa knott 23:32 Apr 6, 2003 (UTC) ---- I am not happy with the sentence from the introduction where it says that particles oscilate around a fixed point. This is only true under "stationary" conditions, as every surfer knows. Which terminology can be used to describe phenomena like surf? ---- i am not happy with this recent addition, waves in ponds are circular: User:Waveguy 03:27, 28 Oct 2003 (UTC) ripple tanks on the surface of a pond are actually a combination of transverse and longitudinal waves; therefore, the points on the surface follow elliptical paths. I'm sorry. But I think that it is the 'wavefront' of the 'pond waves' (in case the initial disturbance is localized e.g. by throwing a stone in the pond)that is circular and not the nature of 'wave'. Any suggestions? User: Rahuljp :Your right Rahuljp. The ripple spread out in a circular pattern, but a point on the suface does not necessarily follow a sinusiodial path. Perhaps a diagram would make the matter clearer? (I'll get to work on one right away)User:Theresa knott 16:54, 6 Nov 2003 (UTC) Thank you Theresa knott. But this does suggest that I did not use the correct language. Can you do it? Rahuljp :Personally I don't think I can do any better than you. IMO it's practically impossible to convey abstract scientific ideas with words. Pictures are much better. User:Theresa knott 17:13, 6 Nov 2003 (UTC) : Good job, Theresa. Rahuljp Thanks.I'm glad you liked it User:Theresa knott 11:40, 14 Nov 2003 (UTC) ---- I'm confused about ripples. Is it possible to provide an explanation of how a wave front moves? That is, consider the first wave front moving across a pond. At some moment a particle on the surface of the pond will be higher than it was previously. On the face of it, that is paradoxical. It is especially confusing since the water itself does not move with the wavefront--it's not like snow being pushed along by a snowplow. What is the explanation for how a bulge shape can move along the surface of the water? -- User:RussAbbott ---- Requestion peer review at wave vector. I just sort of made up this definition basd on what I've seen in papers and on some math website. I think it's okay, but see what you think. --User:Chinasaur 02:07, May 29, 2004 (UTC) ==Cleanup== Several sections of this article need cleanup. The section Media is misleading (a general medium may by any combination or none of the classifications given). The secion on The wave equation also needs some rewriting, particuarly to avoid repeated use of "In the most general" and to explain the meaning of the various symbols used (x, y, z, and t) :done User:Ancheta Wis 08:36, 4 May 2005 (UTC)

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