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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What is the dominant cause for ocean waves at a beach?
What is the dominant cause for ocean waves at a beach? Are they the result of wind/pressure difference? If so, the waves do seem to exist in similar intensity even during relative quiet times of the ...
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607 views
Phase and Group Velocity of Electromagnetic Waves
Moving charges produce oscillating electric and magnetic fields -we have an electromagnetic wave.
In terms of moving charges or at the level of charges, what is phase velocity and group velocity of ...
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1answer
152 views
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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1answer
45 views
A Doppler Effect problem with a moving medium
I tried solving the following question and started having multiple doubts:
Two cars A and B are moving towards each other with some speed $25$ m/s. Wind is blowing with speed $5$ m/s in the ...
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1answer
76 views
Can you “fold” EM or light waves? (i.e) long wave that is reflected by mirror in fragments - like in the game “Snake”
So, I was reading about the Casimir effect. Two mirrors facing each other attract to each other in a vacuum. The reason is due to pressure exerted on those mirrors from the multitude of EM waves (like ...
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1answer
201 views
Wave pulse on a freely falling rope
Consider a rope hanging from the ceiling (massive / massless irrelevant, I suppose). A wave pulse is set up on the rope. Just as the wave pulse starts propagating on this rope, the top of the rope is ...
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2answers
633 views
Group Velocity and Phase Velocity of Matter Wave?
In quantum mechanics, what is the difference between group velocity and phase velocity of matter wave? How can it also be that phase velocity of matter wave always exceeds the speed of light?
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1answer
242 views
Lorentz invariance of a frequency- and wavelength- dependent dielectric tensor
Suppose we have a material described by a dielectric tensor $\bar{\epsilon}$. In frequency domain, this tensor depends on the wave frequency $\omega$ and the wave vector $\vec{k}$.
Clearly not all ...
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1answer
304 views
Frequency response of infinite line source
Let's say I have an infinite line source in 3d wave medium, like a pulsating cylinder, emitting a broadband noisy signal. I know that the pressure falls off at 3 dB per doubling in distance, unlike a ...
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1answer
61 views
How is a one position shift of an interferometer fringe pattern defined?
When Michelson and Morley conducted their 1887 interferometer experiment, they were expecting a fringe pattern shift of 0.4 (see the chart at http://en.wikipedia.org/wiki/Michelson-Morley_experiment). ...
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1answer
82 views
Critical bathymetric profile to maximize surge and minimize breaking?
Reading about storm surge, I found it fascinating that the gradual slope of the Gulf Coast of Florida resulted in a much higher storm surge but much lower energy release in breaking waves.
Is there ...
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1answer
70 views
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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2answers
485 views
coherence length
Suppose i have two waves emanating from a point source. The waves start out completely in phase.
Is the coherence length consistently defined as the length at which these two waves achieve a phase ...
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3answers
957 views
What's a good textbook to learn about waves and oscillations?
I'm taking a course on waves and oscillations using Crawford from the Berkeley series (out of print excluding international copies), and would like to know if anyone has any suggestions for a better ...
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2answers
262 views
Why are AC quantities represented by sine waves always?
Usually we use a sinusoidal wave form to represent a alternating quantity. Why not a cosinusoidal wave or a ramp wave form?
In sine wave forms we can indicate the maximum and minimum amplitude and ...
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2answers
194 views
A question on intereference experiment with water waves as given in the Feynman Lectures on Physics
I have a question related to the interference (thought)experiment with water waves given in the book Feynman Lectures on Physics Vol.3. When only one hole (hole 1) is open the measured wave intensity ...
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3answers
875 views
How is electromagnetic wave variation distributed in space?
Imagine an electromagnetic wave (a monochromatic one for example)
The electric field amplitude, and its variations travel in the propagation direction.
So, if there really exists a propagation ...
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1answer
1k views
Spherical wave as sum of plane waves
How can we do this computation?
$\iiint_{R^3} \frac{e^{ik'r}}{r} e^{ik_1x+k_2y+k_3z}dx dy dz$
where $r=\sqrt{x^2+y^2+z^2}$ ? I think we must use distributions...
Physically, it's equivalent to ...
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1answer
120 views
Can light be canceled by merging with an inverted wave?
Can light waves be canceled by merging them with their inverted waves? Seems like it would violate conservation of energy but waves are added together when they overlap, right? Where is the flaw in ...
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2answers
110 views
What is the history behind the factors of 3 in the classification of electromagnetic radiation?
What is the history behind the factors of 3 in the classification of electromagnetic radiation?
See e.g. http://en.wikipedia.org/wiki/Radio_spectrum#By_frequency
Is this (just) inherited from the ...
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2answers
376 views
Galilean transformation of wave equation
I have this general wave equation:
\begin{equation}
\dfrac{\partial^2 \psi}{\partial x^2}+\dfrac{\partial^2 \psi}{\partial y^2}-\dfrac{1}{c^2}\dfrac{\partial^2 \psi}{\partial t^2}=0
\end{equation}
...
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2answers
888 views
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.
...
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2answers
367 views
Does space have to be filled with charged particles to carry electromagnetic waves?
I'm a newbie here so have mercy.
I'm studying electromagnetic waves. This is the propagation of energy via the vibration of charged particles, as I understand it.
A charged particle could be like ...
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2answers
852 views
Wave / particle duality question for sound and light
Sound is usually referred to as just "sound waves" - we do not talk about a "sound particle" and only as a wave or "matter wave."
Could something similar apply to light i.e. that there really is no ...
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3answers
363 views
Confused over complex representation of the wave
My quantum mechanics textbook says that the following is a representation of a wave traveling in the +$x$ direction:$$\Psi(x,t)=Ae^{i\left(kx-\omega t\right)}\tag1$$
I'm having trouble visualizing ...
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2answers
205 views
Why is $\Delta x \Delta k \approx 1$ in any pulse?
In my physics textbook, it says that for any pulse, if $\Delta x$ becomes smaller, $\Delta k$ becomes larger where $k$ refers to $2\pi/\lambda$ and $x$ is x-axis displacement, as described by $\Delta ...
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3answers
690 views
Reconciling refraction with particle theory and wave theory
I have searched the web for good answers to why refraction occurs when light moves from one medium to another with different density. I have limited background in physics and want to know if there is ...
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2answers
141 views
Utility of displacements potentials in geophysics
In the elasticity theory, you can derive a wave equation from the fundamental equation of motion for an elastic linear homogeneous isotropic medium:
$\rho \partial^2_t \overline{u} = \mu \nabla^2 ...
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1answer
49 views
Energy in a wind instrument?
My physics teacher said that he saw a guy playing a very large wind instrument on TV, and the guy apparently calculated that the total energy present in the instrument when he was playing was almost ...
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3answers
77 views
How to determine the direction of medium's displacement vectors of a standing wave?
Consider the following problem taken from a problem booklet. My questions are:
What is displacement vector?
And how to determine the direction of displacement vector at a certain point?
Where is the ...
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2answers
120 views
Why is there a wave on the water surface when I put something in the water?
We've started doing waves in our physics class, but we're doing things very quickly and the teacher doesn't explain anything. And I don't understand why waves work.
I was thinking that when I fill a ...
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3answers
492 views
Recently publicized experiment on destructive interference between two laser beams
Recently I've had several non-physicist friends ask me, independently of each other, about an experiment where two collinear laser beams destructively interfere along a certain length. Everybody wants ...
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2answers
93 views
Sound Wave Propagation: Why HF are more specular while LF are more omni
The propagation of high frequencies sound waves is more directional (specular), and they don't diffract as much as low frequencies. Low-frequencies diffract and thus propagate in a more omni-spherical ...
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2answers
154 views
Can wind blowing on smooth water create speckle interference patterns?
On a calm smooth lake, or even a large rain puddle, I've seen transient rough patches on the surface suddenly appear and disappear, and sometimes move across the water some distance before ...
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1answer
97 views
How can we test if something is a wave?
More specifically, I want to understand why a wave is a wave but a wave packet is not considered a wave (as discussed in this question).
I would think that if something have these characteristics: 1. ...
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3answers
619 views
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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3answers
460 views
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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2answers
182 views
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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1answer
224 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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2answers
534 views
A basic question on the derivation of the wave equation
Today I saw the derivation of the wave equation in class, and I did not understand the following step.
We are modeling a uniform-density string as being made up of tiny masses spaced a small amount ...
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1answer
37 views
Relation of color and frequency for the visible spectrum
In this question the OP is looking for a way to see light that is outside of the visible spectrum without using electronic sensors. This got me wondering about the visible spectrum itself. Typically ...
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1answer
193 views
Reflection of sound waves
I was doing a physics experiment, and i encountered a question which i couldnt answer. The experiment was about using a radar technique to measure the speed of sound. The apparatus was a plastic tube ...
2
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1answer
157 views
How can Hilbert spaces be used to study the harmonics of vibrating strings?
The overtones of a vibrating string.
These are eigenfunctions of an associated Sturm–Liouville problem.
The eigenvalues 1,1/2,1/3,… form the (musical) harmonic series.
How can Hilbert spaces be ...
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1answer
211 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 ...
2
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1answer
298 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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2answers
305 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
73 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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1answer
162 views
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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5answers
414 views
Radio waves within an atom
What effect does the quantum world have on radio waves? For example, if I could shrink myself down and stand on the nucleus (or even smaller sub atomic particles making up the nucleus) with a device ...
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1answer
407 views
What are examples of Solutions of Newton's Laws that have analogs to Solutions of the Wave Equation?
The idea is to give examples of processes that deal with properties of a particle that have clear wave analogues.
