Questions tagged [waves]

Waves are disturbances that propagate through 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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Galilean transformation of the 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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Why does speed of light have to be constant?

My question is not about why speed of light has a particular constant value which has been sufficiently addressed in other questions on SE already. I want to know whether the fact that speed of light ...
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How quickly is motion transferred in a solid object?

Just for example: assume an iron bar one foot in length. If you push on one end, the entire bar will move. This seems instantaneous. but actually, from my understanding, the atoms all push against ...
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Need mathematical explanation for different musical notes sound different on different instruments

I am not expert in music. There are number of musical instruments. One (especially a person who knows about music) can blindly recognize which instrument is being played just by listening to it. I ...
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Why doesn't the magnetic field polarize when polarizing light?

If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?
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Why does energy in earthquake waves seem to go up with the three halves power?

My question might be based on a false premise, so here's why I asked. If you look up the meaning of the moment magnitude scale for measuring earthquake size, the articles usually say that each ...
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Is a soundproofed wall really only as strong as its weakest area?

I've seen a few questions about sound waves and sound travel here on Physics SE, so I'm hoping this question is a good fit for this site. During my internet research on soundproofing, I've come ...
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What exactly is the "coherence" between waves?

I know, by definition, that coherence means that a pair of waves have constant phase difference. What does this mean? Does it mean they always have a 360 degrees, or 0 degrees phase difference? Or ...
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De Broglie wavelength, frequency and velocity - interpretation

Two fundamental equations regarding wave-particle duality are: $$ \lambda = \frac{h}{p}, \\ \nu = E/h .$$ We talk about de Broglie wavelength, is it meaningful to talk about de Broglie frequency ($\...
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Does light have timbre? [duplicate]

Timbre is a property associated with the shape of a sound wave, that is, the coefficients of the discrete Fourier transform of the corresponding signal. This is why a violin and a piano can each play ...
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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. ...
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Huygens' Principle and Ocean Waves

Ocean waves can travel in any direction, but waves breaking on the sea-shore are usually approximately parallel to the line of the beach. How can Huygens' principle explain this phenomenon? Does it ...
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Calculating Energy of a Wave

So my physics examinations are coming up and I was going through my notes on waves, but I realized that there were some discrepancies. In my notes, the energy of a wave is directly proportional to ...
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Are pure mechanical evanescent waves possible?

Consider a lattice of massive points connected by harmonic springs, with zero or periodic boundary conditions. If we make a repeating pattern of $N$ varying masses, the system will have $N$ bands of ...
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Optimal slit width in Young's double slit experiment

I'm trying to do Young's double slit experiment at home. Note that I don't have a laser, only a torch. I could get a bulb or use a candle though, if it helps I built the slits by cutting into a ...
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Shouldn't sound travel better through doors?

Sound travels much faster in solids than liquids and gases. Then why do we hear a fainter sound from the other room if we close the door than open it? As sound travels faster through solids......
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Does a square wave "smooth out" in the air?

I understand that playing a square wave from speakers cannot produce a PERFECTLY sharp division between compression and rarefaction. But it's sharp enough to sound distinctly different from a sine ...
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How to model the form of a surface water wave?

Normal surface water waves, as generated by wind, do not have sine form but wave peak is higher and shorter than wave trough with different wave steepness. What parameters characterize such a surface ...
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What's the optimal shape for a continuous Galilean Cannon?

A Galilean Cannon is a toy similar to the famous basketball-and-tennis-ball demonstration. You take a tennis ball, balance it on top a basketball, and drop them both. The tennis ball will bounce up to ...
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Can gravitational waves resonate?

Can gravitational waves resonate? - Perhaps by creating standing wave interference in a cavity? Could that feasibly happen either in nature or by engineering?
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Is it better to call the doppler effect a change in wavelength or frequency?

Why is it preferable to say that the doppler effect causes a shift in frequency rather than a shift in wavelength? I often read on websites that they define the doppler effect as a change in frequency....
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Shape of wall's deformation wave caused by baseball's impact

Clicking through this year's top sports pictures, I stumbled upon this one. I was wondering about the shape the baseball is leaving on the wall. What phenomenon causes this peculiar shape? Why is it ...
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How do water waves scale up as the size of a bathtub scales up?

If I fill a bathtub with water to the point that it is spilling out of the far end of the tub, the waves in the tub caused by the water coming into the basin stabilize at a given height -- roughly two ...
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Motivating classical wave equation PDE

I'm teaching a geometry course covering spectral problems, using eigenvalues of the Laplace operator for shape analysis ("Can you hear the shape of a drum?"). I thought I'd cover where the wave ...
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Boundary layer theory in fluids learning resources

I'm trying to understand boundary layer theory in fluids. All I've found are dimensional arguments, order of magnitude arguments, etc... What I'm looking for is more mathematically sound arguments. ...
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Why do I hear voices when I touch my turntable needle?

So I was trying to figure out the reason why my old (and probably sufficiently damaged) needle on my phonograph (turntable) was not working like it was a little while ago. With my headphones on, I ...
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Why does the interference pattern change with given relation when the source slit changes?

Why should the dependence relation be like $${\frac{s}{S}}<{\frac{\lambda}{d}}$$ for the interference condition to be seen? Where $s$ is the width of the source slit and $S$ is the distance ...
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Are matter waves transverse and can they be polarized?

Are matter waves transverse and can they be polarized? What I know:I'm aware of the de Broglie matter waves hypothesis and de Broglie wavelength relation(at a very basic level as part of high school ...
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What is considered a wavelength?

What is considered a wavelength? I am getting confused here. I keep seeing one wavelength is the distance when the wave repeats itself. So at the two highest points that's the wavelength. Now I'm ...
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What happens when the amplitudes of interfering waves is different in the phenomenon of beats?

I had read that for the formation of beats, two waves must interfere such that they have similar frequencies but not identical, and their amplitudes should be identical. I don't understand why should ...
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Why light shows its wave-like properties only when it interacts with objects with dimensions close to the wavelength of light?

In Young's Double Slit Experiment, we were taught that light behaves as a wave here because the width of the slits are very close to the wavelength of light itself. But why does light behave like a ...
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What is the meaning of the word "particle" in particle physics?

I want to use Matt Strassler's definition of the word "particle" as a specific example: Matt Strassler writes: (1) "...all the elementary “particles” (i.e. quanta) of nature are quanta of waves ...
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Can two waves interfere head on?

Can two waves (like sound or electromagnetic waves) interfere head on? If yes, and suppose they are out of phase with each other and thus interfere destructively, where does the energy of the waves go?...
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Why does fringe width in double slit experiment remain constant if slits get narrower?

The fringe width produced on a screen remains constant as the two double slits get narrower, but you are able to see more fringes on screen. I don't understand why the fringe width would remain at the ...
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Does plucking a guitar string create a standing wave?

About two weeks ago there was a mock test in Korea, and a physics question asked if a plucked guitar (it was actually a gayageum, a traditional instrument, but I'll just call it a guitar for ...
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Is this animated gif an accurate representation of EM waves?

From multiple sources, I learned that, in EM waves, electric field vectors are perpendicular to magnetic field vectors and both are perdendicular to the direction of propagation. On this gif, which ...
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Why do we use decibels instead of just using intensity to measure how loud things are?

In my physics book, it says that in the human ear, the sensation of loudness is approximately logarithmic. And that the relative sound intensity is directly proportional to a logarithmic ratio ...
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Why intensity of light(wave) is proportional to the square of its amplitude? [duplicate]

I am confused, Classical wave theory says that Intensity of the light(wave) is the proportional to square of the amplitude. How intensity is proportional to the square of the amplitude?
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Question on wave interference?

When dealing with double slit interference or interference of waves from numerous slits, the equation $nλ = d \sin θ$. However I do not understand why for calculating the angle for maxima and minima ...
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Seeming violation-wave travelling faster than speed of light

Consider the basic relation $$E=\sqrt{(pc)^2+(mc^2)^2}.$$ Every particle possesses a wave nature and it depends on the situation in which one among the two is perceptible... Consider a particle with ...
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A question on using Fourier decomposition to solve the Klein Gordon equation

Given the Klein Gordon equation $$\left(\Box +m^{2}\right)\phi(t,\mathbf{x})=0$$ it is possible to find a solution $\phi(t,\mathbf{x})$ by carrying out a Fourier decomposition of the scalar field $\...
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Why can't light penetrate solid objects?

Light is combination of perpendicular electric and magnetic fields, since electric fields penetrate a conductor, why can't light travel in them? I think my argument does sound stupid, but I can't ...
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What is the difference between a pulse and a wave?

I wanted to ask what is the difference between a pulse and a wave? According to the definitions of them, they are almost the same. In the websites I looked at, the difference between them was ...
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Can someone explain how water from a garden hose can propagate in a sine/cosine wave?

A video posted on Youtube. How does this phenomenon work? I know he is using frequency to propagate water in a sine/cosine wave, but how does it exactly work this way? Why do we see it as if its ...
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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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What is the basis of Huygens principle?

When we were studying mechanical waves like sound waves, and waves on strings in class, we never studied Huygens' principle with these - and nor did we really derive the laws of reflection or ...
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Why do we think of light as a wave?

I've read that light travels in a straight line and has a wavelength of 400nm to 700nm. But I don't understand why does it have a wavelength and what creates its wavelength? I agree with the concept ...
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Interpreting physical meaning of normal modes

What really is a normal mode? Maybe it's because of my teachers but I find it really abstract. I know that "numerically" corresponds to the eigenvectors of the equation $\ddot{X}= -M^{-1}KX$ ...
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Does a wave experiencing a total internal reflection penetrate the medium in any way?

Let me explain my concern usingn this picture: At the point of total internal reflection does a fraction of the wave get into medium 2? I would imagine it should happen because of the uncertainty ...
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Why doesn't the speed of the wind have an effect on the apparent frequency?

A boy is standing in front of stationary train. The train blows a horn of $400Hz$ frequency . If the wind is blowing from train to boy at speed at $30m/s$, the apparent frequency of sound heard by the ...

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