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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What happens to the energy when waves perfectly cancel each other?
What happens to the energy when waves completely cancel each other out via destructive interference? It seems like the energy just disappears, but that would violate the law of energy conservation.
My ...
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Validity of naively computing the de Broglie wavelength of a macroscopic object
Many introductory quantum mechanics textbooks include simple exercises on computing the de Broglie wavelength of macroscopic objects, often contrasting the results with that of a proton, etc.
For ...
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Why do prisms work (why is refraction frequency dependent)?
It is well known that a prism can "split light" by separating different frequencies of light:
Many sources state that the reason this happens is that the index of refraction is different for ...
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Phase shift of 180 degrees of transversal wave on reflection from denser medium
Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave, when reflected from an optically denser medium?
I tried searching for ...
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What is the physical significance of the imaginary part when plane waves are represented as $e^{i(kx-\omega t)}$?
I've read that plane wave equations can be represented in various forms, like sine or cosine curves, etc. What is the part of the imaginary unit $i$ when plane waves are represented in the form
$$f(x) ...
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Amplitude of an electromagnetic wave containing a single photon
Given a light pulse in vacuum containing a single photon with an energy $E=h\nu$, what is the peak value of the electric / magnetic field?
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How do mirrors work?
My physics professor explained to me that electromagnetic waves are consisted of two components - electric and magnetic - which cause each other.
Which part of the mirror actually reflects the wave?
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Energy conservation and interference
I have a problem with energy conservation in case of interfering waves.
Imagine two harmonic waves with amplitudes $A$. They both carry energy that is proportional to $A^2$, so the total energy is ...
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In what medium are non-mechanical waves a disturbance? The aether?
The most basic and simple definition of a wave is that it is a disturbance in a medium. Then what are non-mechanical waves disturbance in? The aether? Please explain to me this question in detail as ...
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How can standing waves be produced in an open organ pipe if the ends are open?
How can standing waves be produced in an open organ pipe even though both of its ends are open? Can someone explain with more clarity?
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Significance of wave number?
Till now all I know about the wave number is its formula i.e. ${\frac{2\pi}{\lambda}}$. I always wanted to know what it really means. So can anyone please, explain me its physical significance?
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What does a de Broglie wave look like?
What does a de Broglie wave look like?
Are de Broglie waves transverse or longitudinal?
Can they be polarized?
What about the de Broglie wave of a ground state neutral spin-zero Helium 4 atom?
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What Exactly is a Shock Wave?
The Wikipedia defintion of a shock wave pretty much sums up all I've found online about what a shock wave is:
A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries ...
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How is the Schroedinger equation a wave equation?
Wave equations take the form:
$$\frac{ \partial^2 f} {\partial t^2} = c^2 \nabla ^2f$$
But the Schroedinger equation takes the form:
$$i \hbar \frac{ \partial f} {\partial t} = - \frac{\hbar ^2}{...
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Patterns in laminar flow of tap water
This is a simple experiment that anyone can do at home. Open your tap so that the water maintains a laminar flow, and the cross section of flow is considerably thin. Place your finger 3-4 cm below the ...
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Reflection of sound waves from the open end of an organ pipe & relationship b/w nodes & pressure [duplicate]
We know that standing waves are created when any wave traveling along the medium will reflect back when they reach the end. But in an open organ pipe, there is nothing to oppose the wave and reflect ...
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Can I compute the mass of a coin based on the sound of its fall?
The other day, I bumped my bookshelf and a coin fell down. This gave me an idea. Is it possible to compute the mass of a coin, based on the sound emitted when it falls?
I think that there should be a ...
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Why is Huygens' principle only valid in an odd number of spatial dimensions?
Apparently Huygens' principle is only valid in an odd number of spatial dimensions:
https://mathoverflow.net/a/5396/21349
Huygen's principle in curved spacetimes
Why is this?
[EDIT] This is ...
user4552
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Existence of monochromatic pulses?
Why there can not be a monochromatic pulse? My physics professor told us that we can't generate a monochromatic light pulse and I was wondering what are the physical limitations causing this.
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Derivation of 1D wave equation
I know a similar post has been made about this, but it has been quite some time since then, and none of the answers satisfy me.
I want to derive the 1D-wave equation from the knowledge that what we ...
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What restrictions on time boundary conditions does it have to use Fourier transform to solve wave equation?
The wave equation can be solved using Fourier transform, by assuming a solution of the form of
$$\mathbf{E}(x,y,z,t)~=~\mathbf{E}(x,y,z)e^{j\omega t}$$
and then reducing the equation to the Helmholtz ...
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Radio antenna producing waves in the visible spectrum [closed]
If a radio could produce waves in the visible light spectrum, what would the result be?
This is a thought experiment that I've pondered for a few years now. I realize there are a few/many real-world ...
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Why do travelling waves continue after amplitude sum = 0?
My professor asked an interesting question at the end of the last class, but I can't figure out the answer. The question is this (recalled from memory):
There are two travelling wave pulses moving in ...
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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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If light rays obey to the wave equation, why can they be thought as straight lines?
I'm a newbie with physics but I'm wondering how a ray of light can essentially be represented. I have always known that a ray of light proceeds in a straight line until it encounters another object (...
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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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Why does the frequency of a wave remain constant?
They say the frequency of a wave is its fundamental character, thus remain constant throughout its propagation regardless the medium through which it travels. Could anyone explain why frequency of ...
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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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Optical explanation of images of stars?
Very often when viewing pictures of the cosmos taken by telescopes, one can observe that larger/brighter stars do not appear precisely as points/circles on the image. Indeed, the brighter the light ...
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Why does wavelength affect diffraction?
I have seen many questions of this type but I could nowhere find the answer to "why". I know this is a phenomenon which has been seen and discovered and we know it happens and how it happens. But my ...
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How can transverse waves on a string carry longitudinal momentum?
In general, if a wave carries energy density $u$ with velocity $v$, it also carries momentum density $u/v$. I've seen this explicitly shown for electromagnetic waves and (longitudinal) sound waves.
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Do the electric and magnetic components of an electromagnetic wave really generate each other?
Frequently when EM waves are taught, it is said that the change in electric field causes a change in the magnetic field, which then causes a change in the electric field, and so on and so forth.
But ...
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What is a wave?
I was watching an outtake of Prof. Brian Cox talking to a tv producer about "gravity waves". Their discussion got a bit side-tracked, because the non-scientist didn't seem to understand what a wave "...
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Frequency of the sound when blowing in a bottle
I'm sure you have tried sometime to make a sound by blowing in an empty bottle. Of course, the tone/frequency of the sound modifies if the bottle changes its shape, volume, etc.
I am interested in ...
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What happens to waves when they hit smaller apertures than their wavelenghts?
I was wondering this for quite a long time now. Let's say you have a water wave (like ripples, not the ones you see during tsunamis) with wavelength 10 m. Imagine you put a boundary with an opening of ...
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Why can we distinguish different pitches in a chord but not different hues of light?
In music, when two or more pitches are played together at the same time, they form a chord. If each pitch has a corresponding wave frequency (a pure, or fundamental, tone), the pitches played together ...
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Wave reflection and open end boundary condition intuition
I need to understand one seemingly simple thing in wave mechanics, so any help is much appreciated!
When a pulse on a string travels to the right toward an open end (like a massless ring that is free ...
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Is it possible to use "negative sound waves" to "cancel out" a sound to create silence?
I saw youtube videos that claimed to do this, although I'm quite certain the videos just excluded sound and lied.
However, I am wondering if the physics of this is actually possible - to create a ...
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What exactly is meant by the wavelength of a photon?
I've been thinking about this for quite some time, and from looking online I haven't found a satisfying answer.
Lots of photons, such as visible-light photons have very small wavelength (which from ...
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Is light amplitude spatial?
In diagrams I often see light waves depicted as little sine waves that travel through space. And often when describing polarizers, the explainer will angle their hand to show the angle of ...
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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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Wave equation: $y=A \sin(\omega t-kx)$ or $y=A\sin(kx-\omega t)$?
What is correct wave equation:
$y=A \sin(\omega t-kx)$ or $y=A\sin(kx-\omega t)$?
How are these wave equations used in the positive $x$-direction
and negative $x$-direction?
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Why exactly does diffraction occur?
Why do waves that were traveling in a straight direction change direction when passing through an opening?
I thought that the waves (red arrow) when colliding with the wall bounce in the opposite ...
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Theory behind patterns formed on Chladni plates?
In this video of vibrating Chladni plates we can see small sand particles align themselves into different interesting patterns (also shown in the image below) which correspond to some particular ...
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How does Huygens Principle incorporate the unidirectional property of a traveling wave?
I was reading French's Vibrations & Waves where he discusses Huygens-Frensel Principle.
The principle talks about how secondary sources give rise to secondary wavelets to form the displaced ...
user36790
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Popular depictions of electromagnetic wave: is there an error?
Here are some depictions of electromagnetic wave, similar to the depictions in other places:
Isn't there an error? It is logical to presume that the electric field should have maximum when magnetic ...
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How to "derive" the wave equation without refering to strings?
The wave equation in $3$ dimensions is simply:
$$\nabla^2\psi = \dfrac{1}{v^2} \dfrac{\partial^2}{\partial t^2}\psi,$$
and the intuition behind this is that at each point of space with coordinates $(...
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Waves in water always circular
I have had a question since childhood. Why do we always get circular waves (ripples) in water even when we throw irregularly shaped object in it?
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Why is the wave equation so pervasive?
The homogenous wave equation can be expressed in covariant form as
$$ \Box^2 \varphi = 0 $$
where $\Box^2$ is the D'Alembert operator and $\varphi$ is some physical field.
The acoustic wave ...
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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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