# 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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### How do Standing Waves satisfy the criteria in order to be considered as Waves?

Why are standing waves even categorised as waves if they don't transfer energy from one point to another? Waves are generally defined as disturbances that transfer energy but standing waves don't ...
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### Can we use the equations $-AωSin(ωt+φ)$ and $AωSin(ωt+φ)$ interchangably?

My book says that, For a simple harmonic motion, velocity of the particle = -AωSin(ωt+φ) Now, assuming φ to be π/2, in the next sentence, they say that, maximum velocity = Aω. Why have they simply ...
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### Is it also the case that $\langle f(t)\rangle = 0$ for $f(t) = A \cos(\omega t)$? And how does one get that $\langle f(t)\rangle = 0$?

This page discusses time averaging. It says that time averages are often important when considering oscillating waves of the form $f(t) = A \sin(\omega t)$, where $\omega$ is the angular frequency and ...
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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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### The resonance frequency of a steel ball

I wanted to find the resonance frequency of a steel ball. I assume that gradient disappears on the surface of a ball. I knew that I can find it solving 3D wave equation in spherical coordinates. Due ...
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### Speed $v$ of a wave on a tightrope

Starting from D'Alembert's general wave equation we can find the propagation speed of an impulse along a tightrope as a function of linear mass density, $$\boxed{v= \sqrt{\frac \tau \mu}} \tag 1$$ ...
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### Do acoustic waves in liquid crystals have transverse modes?

According to a previous question: Modes of propagation in media acoustic waves in media can be decomposed in two kinds of modes: longitudinal and transverse; solids being the only one where they are ...
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### Wave packet in quantum mechanics?

When we talk about light waves or EM waves, we simply say that the wave packet is the superposition of other waves of different wavelengths. In quantum mechanics, we say the same thing; the ...
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### The lowest possible frequency of sound wave

What is the lowest possible frequency of sound waves. I imagine that if a plate vibrates slower and slower it stops producing sound and starts to just 'move' the air around. What is this minimum ...
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### What is the difference between beats and wave packets?

What is the specific difference between beats and wave packets. According to my book both are the formed by superposition of two waves having slightly different frequencies
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### What is the $y$-axis in an electromagnetic wave?

Apologies if my question is unclear, any help to clarify it along the way is most welcome. I'm confused about what we mean when we say electromagnetic 'waves' (say visible light). In the usual mental ...
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### Longitudal waves. Proof of $\Delta p=B \frac{\partial s}{\partial x}$

I have trouble understanding some derivations about longitudal waves. I need to derive $\Delta p=B \frac{\partial s}{\partial x}$ from $\Delta p=B \frac{\Delta V}{V}$ knowing that $\Delta V=A\Delta s$...
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### Why is $kx−ωt$ a constant for a travelling wave?

In my physics textbook, there is a statement like this: The motion of a fixed phase point on a progressive wave is given by $kx−ωt$= a constant. What does this mean? Why is it a constant? Does fixed ...
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### What’s the difference between energy in an electromagnetic wave and transmit power?

As I understand, Energy of an electromagnetic wave has a direct relationship to frequency. A higher Energy wave is smaller in length at greater frequency. But Transmit Power can be increased without ...
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### What is the Physics Behind Invisibility of Writing with any color over Black color

If I Write something with a black pen on a piece of paper and try to scribble something with say, a red pen over it, Why can't I view it as a separate entity from the black ink?
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### Wave propagation through conductors

During wave propagation through conductor, why is the current density out of phase with electric field ? When the oscillating electric field applies a driving force on the free electrons, they will ...
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### What exactly is longitudinal polarization?

See the title. I keep reading about longitudinal polarization in difference scenarios (muons, especially), however I have been unable to find a clear definition of what it is. I would appreciate an ...
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### Can we decompose sound like white light is decomposed (dispersed) in different colors?

When we send white light through a prism, the light is decomposed in the colors that constitute it due to the different velocities which different frequencies. Is there a way to decompose "white ...
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### Why light scattered in a direction at right angles to the incident light always plane-polarised?

In my textbook, it is written that polarisation of light occurs by scattering. When light is incident on small particles of dust, air molecules, etc. it is absorbed and re-radiated by the electrons. ...
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### Is there light where there is no electromagnetic field?

If light is oscillation in the electromagnetic field, then is there light where there is no electromagnetic field? Are there places without any electromagnetic fields?
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### The Feynman Lectures on Physics Interference

From The Feynman Lectures on Physics, Feynman states that: You will remember that the quantitative relationship between I1, I2, and I12 can be expressed in the following way: The instantaneous height ...
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### Can the sound of infinitely long played music be decomposed in sine (or cosine) forms?

Every arbitrary waveform (except non-linear ones) can be decomposed in sine (or cosine) waveforms that spatially extend to infinity. That is if the waveform has a finite spatial extent. But say that I ...
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### Does sound have any meaning in space?

Sound is just an disturbance of partial in a medium and every disturbance need some energy but if there is no medium then there will be no disturbance hence no energy will be dissipated from the ...
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### Is every function that satisfies classical wave equation, represent a wave?

I'm studying about the waves and the classical wave equation where I'm searching out the methods to check whether a function represents a wave or not, and I come up with this question.
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### How does diffraction affect the amplitude of sound?

Let’s say we have a 2D “maze” which represents walls in a space. If we place a sound source somewhere in it, what would be the amplitude at a different point in the maze. Or in a simpler case, given a ...
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### Are all waves periodic?

I'm studying waves, and I am confused about two different definitions of a wave. One place defines a wave as "a propagating dynamic disturbance of one or more quantities". Another says that &...
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### Wave-particle duality seems like an obvious example of a contradiction that people refuse to accept. What am I missing? [duplicate]

We state that electrons are subatomic particles with no known subcomponents. We discover that these electrons behave as waves. We also discover that sometimes, these electrons behave as point-...
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### Why surface water waves are dispersive?

It has been asked again and the answer was that there is a kind of resonance between the wave and the medium. Does anybody know something more about this resonance?
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### A standing wave with different linear mass densities

I have a question about a standing wave with different linear mass densities throughout the string. Suppose that we had a string of linear mass density $\mu$ joined at $x = L$ to a string with linear ...
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### How can Light show dual Nature? [duplicate]

How can Light show dual Nature, It is just saying like, An animal is Dog as well as Cat How can Light exist in dual Nature?,for instance, when can The light show particle nature and when can it show ...
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### Can both magnetic and electric fields induce current from an EM wave?

I was reviewing a homework problem I completed for class, but I saw different explanation that contradict each other. My teacher says that this position for the waves is optimal for maximum induced ...
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### What is the difference between a photon's phase and polarization?

When talking about a photon emitted by a laser device, what is the difference between phase and polarization? Is it redundant to specify both the polarization and the wavefunction's phase? Does a ...
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### Moving charges emit electromagnetic radiation. So can sound waves in ionized air produce light?

Moving charges emit electromagnetic radiation. Sound wave propagation through air involves the vibration of air molecules. So in principle, can sound waves in ionized air produce light? This post does ...
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### On the nature of the light [closed]

How "correct" is our interpretation of the world with the current theories of physics? More specific I wonder how close to truth is the interpretation of the nature of light, for example ...
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### Are the frequencies of standing waves on a non-uniform string harmonic?

For a uniform string, the standing wave frequencies form “harmonics,” which means they are whole-number multiples of the lowest standing wave mode frequency, called the fundamental frequency. For this ...
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### Superposing waves to create visible light

I have a question: Is it possible to create visible light using two other non-coherent waves from the electromagnetic spectrum for example superposing infrared and ultraviolet to create visible light?
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### Time dependence in non-dispersive waves

I'm reading the book "A Student's Guide to Waves" by Daniel A. Fleisch and Laura Kinnaman in an attempt to get quickly up to speed in some of the terminology and maths of waves. At some ...
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### Noise Cancellation - Destructive Interference

We know that active noise cancelling headphones work by playing a signal in your ear which is 180º out of phase with the ambient noise. If we compare the two waves, the peak in one wave is completely ...