Waves are disturbances that propagate throush space and time. Classically, they travelled through a medium, disturbing the particles but not changing their mean position. Electromagnetic waves/particle-waves need no medium; they are disturbances in their respective fields.

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Geometry of wireless signal strength

How does wireless signal strength correspond to distance? RSSI lies between -100 and 0 (at least, on my computer). Let's say I walk a distance x towards the router, and my RSSI goes from -60 to -50. ...
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Superposition of electromagnetic waves

The superposition of two waves is given by $$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$ For sound waves, this ...
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How does gravitation propagate along curved spacetime?

In this wikipedia article it is described how a beam of light, with its locally constant speed, can travel "faster than light". That is to say it travels a distance, which, from a special relativistic ...
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Why is there a 90˚ phase angle between particle velocity and sound pressure in spherical waves?

My text says that in a plane sound wave (or in the far field), particle velocity and pressure is in phase. As we move closer to the sound source (to near field and more spherical waves), the phase ...
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So where is mistake in the formula of wave number (magnitude of wave vector)?

I have following form for wave vector $k_2=n_2 \omega/c_0$. Now because $\omega=2 \pi c/ \lambda$, then $k_2=n_2 \omega/c_0=\frac{n_2 2 \pi c_0}{c_0 \lambda}=\frac{n_2 2 \pi}{\lambda}$. But problem is ...
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What happens to the energy when waves perfectly cancel each other?

What happens to the energy when waves perfectly cancel each other (destructive interference)? It appears that the energy "disappear" but the law of conservation of energy states that it can't be ...
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Reflection of transverse and longitudinal waves

Why is it that when a transverse wave is reflected from a 'rigid' surface, it undergoes a phase change of $\pi$ radians, whereas when a longitudinal wave is reflected from a rigid surface, it does not ...
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174 views

Wave with mass transport?

I don't think this question has been asked on this forum before (at least I didn't find it). In the case of a tsunami, an earthquake generates a wave which will travel with the sea/ocean as the ...
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Physical interpretation of Parseval's theorem

I have read that Parseval's theorem, relating the norm of a function $f$ and the norm of its Fourier transform $g(k)$: \begin{equation} \int |f(x)|^2 dx=\int|g(k)|^2 dk \end{equation} has the ...
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225 views

Why do rain waves form and what is their connection to the texture of the surface they're on?

When it rains and water flows down an inclined street, ripples may form that are carried along with the current. Here's a picture with an example of what I'm talking about I'd like to know what the ...
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How does infrared light 'erase' phosphorescence on zinc sulfide?

I found some sheets of zinc sulfide in my basement that phosphoresce green for up to 24 hours or so after exposure to bright light in the violet range or shorter. One of the first things I tried was ...
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727 views

Does a cycle (in Simple Harmonic Motion) have to equal 2π?

So, I search for the definition of cycle and I get this in Wikipedia: A turn is a unit of angle measurement equal to 360° or 2π radians (or ...). A turn is also referred to as a revolution or ...
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Why no longitudinal electromagnetic waves?

According to wikipedia and other sources, there are no longitudinal electromagnetic waves in free space. I'm wondering why not. Consider an oscillating charged particle as a source of EM waves. Say ...
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3answers
582 views

Is it correct to say that electromagnetic waves does not require a medium?

I can conceive of a particle existing in empty spacetime, but not a wave. A wave appears to me at least, to insist upon a medium for its very definition. I understand that the 19C physicists ...
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1answer
396 views

How was this pressure pulse propagation speed be derived?

Some lecture notes I was reading through claimed that a pressure pulse propagates through a liquid-filled tube (blood in a vein) with the speed $$c=\sqrt{\frac{A}{\rho}\frac{dP}{dA}},$$ where $A$ is ...
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353 views

Is there orbital angular momentum for all particles?

Light as an electromagnetic wave can be polarized in different ways, e.g. linear or circular. As far as I understand it currently this can be compared to the spin direction of a propagation electron ...
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188 views

How to derive a multi-reflection echo from a given single-reflection “trace”

Consider a one-dimensional semi-bounded "ray" (or thin "cylinder") of stratum (or just any homogeneous substance) which has several "features" along it's length (say, thin films). Consider a wave that ...
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Electric field Fourier decomposition

I have the following decomposition for the electric component of light: $$\renewcommand{\vec}[1]{\mathbf{#1}}\vec{E}(\vec r)=\frac1{4\pi^2} \iint_\Omega \vec A(k_x, k_y) \mathrm{e}^{i \vec{k} \cdot ...
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Can a wave propagate in an elastic fluid in the absence of volume forces?

A motion (wave) $\mathbf{x}: \mathcal{B}_0 \times [t_0,t_1] \to \mathcal{E}:$ such that $q-o = \mathbf{x}(p,t)=(p-o)+\mathbf{a}_0 cos(\mathbf{k}_0\cdot(p-o) - \omega_0 t)$ can propagate in an elastic ...
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798 views

How to compute the intensity of a polarized wave going through a polaroid?

If an electromagnetic wave is linearly polarized, the intensity of the light that goes through a polaroid is proportional to the square of the cosine of the angle between the polarization plane and ...
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171 views

What is the electric field part of an EM wave? Radiation field or the induction field?

Look at this image: I wonder if the electric field is from the induction field from a vibrating electron or the radiation field? If it is from the radiation field, as I suppose, than can someone ...
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Angular frequency. Wrong interpretation at Wikipedia?

This and this articles mention that the angular frequency is: number of oscillations per unit of time But this doesn't seem to be correct since the angular ...
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705 views

How does a speaker produce sound?

What I read is that a speaker produces sound by the movement of a coil attached to a cone which moves back and forth. So, If I try to move the coil by hand, would it produce sound? If not, why? or Why ...
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Electromagnetic wave reflection vs. light reflection

Related: x-ray interaction with atmosphere I know that electromagnetic waves of particular frequencies reflect from the ionosphere. And the light (which from one perspective is an electromagnetic ...
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299 views

Wave equation from hooke law - simple question

In the paragraph http://en.wikipedia.org/wiki/Wave_equation#From_Hooke.27s_law it is said, regarding the u(x) function, that Here u(x) measures the distance from the equilibrium of the mass ...
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Does EM radiation (any, i.e. RF), or sound, radiate everywhere at once?

I am having trouble understanding electromagnetic radiation (or waves in general, be it EM or sound). If I have a 1 Watt speaker, is it infinitely divided and spread out so that everyone in every ...
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Why is it necessary for an object to have a bigger size than the wavelength of light in order for us to see it?

I keep hearing this rule that an object must have a bigger size than the wavelength of light in order for us to see it, and though I don't have any professional relationship with physics, I want to ...
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Energy in an EM wave should depend on frequency

I just finished reading Feynman's Lectures on Physics vol.I, §34-9: "The momentum of light". The author explains that there is a relation between the wave 4-vector $k^{\mu}$ and the energy-momentum ...
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447 views

A simple question about the stationary wave and fundamental frequency

Suppose we have 2 fixed end connected with a wire and now we insert a vibrator in the middle of the wire, and resonance occur. How would the fundamental frequency looks like? I know the case when the ...
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1answer
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Relation between wavenumber and propagation constant

What is the exact difference between wavenumber and propagation constant in an electromagnetic wave propagating in a medium such as a transmission line, cause i am a bit confused. Does it have to do ...
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83 views

Close electric field lines in wave guides

In a wave guide, graphics of propagation of Transversal Magnetic modes show closed field lines for the electric field. For example, for a rectangular guide: $E_x (x,y,z) = \frac {-j\beta m \pi}{a ...
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How does one determine whether an object will make an EM wave refract in a qualitative way?

for example, i have a vague notion that the actual answer is that the permittivity and permisivity are different in each different material, so all waves refract at every boundary, but we only call it ...
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Confusion concerning the use of wavenumber in exercise about Fabry-Perot etalon

In the exercise we are given that the spectrum of a light source consists of two spectral lines, which both have wavelengths around $500 \text{ nm}$ and the separation between them - given in ...
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How to predict sea waves length/height?

I would like to know which are the best methods used to predict sea waves characteristics (particularly predict length/height given water depth and wind speed) and how are they used. My major is ...
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447 views

Counting the number of modes

The exercise is the following Show that the number $N(\lambda) \, \mathrm d \lambda$ of standing electromagnetic waves (modes) in a large cube of volume $V$ with wavelengts within the interval ...
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Why is Polarization of a wave important, and what happens when a wave is polarized in all three dimensions?

I don't quite understand this, I understand that given a wave traveling in a certain direction, it will be polarized in the direction its not travelling in, so if its travelling in the Z direction, k ...
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Why do bass tones travel through walls?

I was in the shower while my roommate was listening to music and got to thinking about the fact that I could only hear the bass and lower drums through the walls. Why is this? The two possibilities I ...
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316 views

How much energy is contained in a 40 meter wave?

Consider a wave that stands 40 meters high in the sea on very deep water. How much energy would approximately be contained in this wave if it was 100 meters wide and had been produced by wind? Is ...
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363 views

Speed of Light, Photons or WaveSpeed?

The speed of light is almost 300 000 km/s. The photons have a speed along the wave, and the wave have a speed straight forwards. What is the speed of light? Is it the speed the photons have along ...
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Testing my understanding of QM - The Double Slit Experiment without the slit

First off, sorry to throw in another question from someone who hasn't studied the maths. I'd like to see if I have a correct (if very basic and non-mathematical) understanding of the wave and ...
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why is mechanical waves faster in denser medium while EM waves slower?

Why is it that mechanical waves/longitudinal waves/sound travel faster in a denser/stiffer medium as in steel compared to say air, while EM waves/trasverse waves/light travels slower in a (optically) ...
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How can a sine wave represent a longitudinal wave?

I envision a longitudinal wave as a series of vertical lines like that drawn on the board in an introductory physics class. This image contains no angles. Sound is a longitudinal wave. Some ...
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Radar Frequency Bandwidth

I've come across an interesting question in the course of doing some exam review in a quantum mechanics book and thought I'd share it here. "What must be the frequency bandwidth of the detecting and ...
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3answers
830 views

Sine wave, $\pi$ and frequency

Please explain the relation $\sin(2\pi ft)$ such that how the $\pi$ (which is actually circumference/diameter of a circle) relates with the sine wave which is having a longitudinal vibration?
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Does a finite wave necessarily have to be non-monochromatic in reality?

Does a finite wave necessarily have to be non-monochromatic in reality, or is that implication just a result of the mathematical analysis? I always wonder at these sort of things that come out of a ...
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What does transport equation represent in terms of physical quantities?

In my math course we're taught to solve PDE (partial derivative equations) like transport equation: $$ c\frac{\partial u}{\partial x} +\frac{\partial u}{\partial t}~=~0. $$ If $u(x,t)$ is the ...
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Transparent boundary condition [closed]

I am interested in the finite-difference beam propagation method and its applications. I try to solve the Helmholtz equation. At first, i would like to solve numerically it for the easiest case, ...
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Why is energy in a wave proportional to amplitude squared

I'm a mathematics student trying to grasp some basics about wave propagation. A sentence I find very often in introductive physics textbooks is the following: In a wave, energy is proportional to ...
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1D Wave mechanics (string)

Suppose I have a wave traveling to the right described by $e^{iw(t-{x\over c})}$. (It obeys the 1D wave equation). AND at $x=0$, there is a mass $M$ fixed to the string such that we have $M{d^2y\over ...
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Speed of a particle in quantum mechanics: phase velocity vs. group velocity

Given that one usually defines two different velocities for a wave, these being the phase velocity and the group velocity, I was asking their meaning for the associated particle in quantum mechanics. ...