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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Unusual waves and one of its parameter

I'm messing up with this java app on the web about waves on a string and i'm really curious about something. The java app is the following : ...
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1answer
72 views

Why is $B=\frac{1}{\omega} k\times E$?

Why can we derrive from $B=\frac{k}{\omega}|E|$ the formula $B=\frac{1}{\omega} k\times E$ ? Obviously, because they are perpendicular, but why is it mathematically legitimate?
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134 views

Why is sometimes the wave function written as $\exp(i(\omega t-kz))$, so ωt and kz are switched?

Is it legitimate to write $-\exp(i(kz-\omega t))$ as $\exp(i(\omega t-kz))$?
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1answer
90 views

Quantum Wavefunctions Without Space

A handful of physicists have a rather peculiar definition of 'nothing' in terms of cosmology. Their claim is that the Universe, assuming it has 0 total energy, could have arisen from nothing but ...
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1answer
146 views

Intensity for Single-Slit Interference Pattern

In the derivation for the equation for the relative intensity of a single-slit interference pattern in my textbook, there is an assumption that I find a bit fishy. I know this equation works, so it ...
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1answer
70 views

Standing Waves. Two questions. Please help! [duplicate]

Every time I read an article/text about standing waves they seem to specifically mention that whenever a wave pulse hits a hard boundary it gets reflected back with it's phase changed through 180 ...
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3answers
356 views

The ubiquitous Planewave Ansatz

In physics, the planewave ansatz (meaning: an educated solution guess) is very ubiquitously used, when solving differential equations, in different domains of physics. E.g. to solve the dispersion ...
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1answer
78 views

Does Red shift affect electron waves? [duplicate]

According to the De-Broglie Wave Hypothesis an electron can be considered to be a wave. Red Shift occurs due to the expansion of space(Cosmological red shift), which must expand even on the scale of ...
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2answers
125 views

Must flow be supersonic for disturbances not to affect upstream?

I'm studying oil production and found a fact that puzzled me. It states that fluid flow downstream of the wellhead must be supercritical in order not to disturb the flow upstream of it. From ...
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1answer
65 views

What happens in extrema cases of red shift?

Red shift is the increase in the wavelength of an electromagnetic wave as it travels through space. If the wave travels for a time long enough can its wavelength increase so much that it becomes ...
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56 views

What is the difference between antiferromagnetism and spin density wave?

It seems that antiferromagnetism can be treated as a special case of spin density wave with wavelength equals to twice of the unit cell. Is that so?
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0answers
2k views

Smallest Wavelength of light possible? [duplicate]

I was thinking about blue-shifting of light and I couldn't help my self but think about the limits of blue shifting mechanism and since we know energy of a photon is directly proportional to the ...
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0answers
145 views

How is it that 62" is the best length for 72Mhz receiver?

According the this article (which was published somewhere in 2005-2008 I think, but it's still comes up first in Google) the best length for a 72Mhz receiver antenna is 62" (~157.5cm). This puzzles me ...
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43 views

How can water waves be transverse when we know that transverse waves are not possible in fluids?

It is said that fluid cannot sustain shear stress so a transverse wave cannot exist in fluids. Well, isn't this contradictory to what see we everyday in the form of water waves?
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43 views

Ray tracing a three-way intersection

I've been studying ray tracing in media with linear velocity-depth functions. One of the key concepts I've come across is the ray parameter, and in particular the idea that the ray parameter is ...
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1answer
66 views

How did the Huygens probe use EM waves to measure wind speeds on Titan?

In the Wikipedia's article on Huygens spacecraft, it was mentioned that one of the experiments was to measure the wind speeds on Titan by Doppler wind experiment. To quote the exact lines, it was ...
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1answer
55 views

Question about wavelength of EM wave in dielectric

Many websites (http://maxwells-equations.com/materials/permittivity.php) lists out the following formula as to how you can compute the wavelength of an EM wave in a dielectric $$\lambda_d = ...
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5answers
864 views

Why do the high frequency waves have the most number of modes?

While reading the Wikipedia page of Ultraviolet Catastrophe, I came across how Rayleigh and Jeans applied the equipartition theorem. They told that each mode must have same energy. Now as the number ...
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1answer
2k views

Converging Lenses with Objects at “Infinity”

Whenever we take the case of an object at infinity, we say that the image formed ends up being a point of light on the focal point if we had put a screen right at the focal point. Now, for my lab, ...
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3answers
3k views

What do we see while watching light? Waves or particles?

I'm trying to understand quantum physics. I'm pretty familiar with it but I can't decide what counts as observing to cause particle behave (at least when it's about lights). So the question is what do ...
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4answers
209 views

Why Light isn't like an Acoustic wave?

I just wanted to know why light isn't an Acoustic wave.Is it because light wave doesn't obey acoustic properties?
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2answers
89 views

A question over the reality of $\sin x$

Harmonic functions are in widespread use in physical descriptions of natural real phenomena. I am just wondering therefore how we can define $\sin(x)$ to be part of a real physical quantity (with ...
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1answer
131 views

Abstract concept of wave propagating on a string

I'm a real beginner in physics with a really basic doubt about waves. Suppose i have a string ( perfect elastic material ) whose left-end i can manipulate ( i can change its heigth ) and whose ...
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1answer
199 views

Diffraction and $k$-space

Regarding diffraction I am a little bit lost reading about reciprocal space and the space of $k$'s. As I understand it the Fourier relationship between a wavepacket $\Psi(\vec r,t)$ and the complex ...
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1answer
71 views

What is the movement of the material point? [closed]

The parametric formulas for movement of a material point are: $x(t) = A \sin (kt)$ $y(t) = B(1 - \sin(kt))$ Describe the movement of the MP. That is the entire question and I can't find a ...
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3answers
285 views

If a tree falls in the forest [closed]

The question of whether or not a tree that falls in the forest makes a sound - if there is nothing or no one around to hear it - comes up frequently at my house. So, my question is: is there any way ...
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3answers
220 views

A misunderstanding regarding infinite square well

Here is a picture of the energy states of infinite potential well. We can see That the first level have a half wavelength which fittes with a full wave of the second level. $$\frac{ \lambda _{1} ...
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3answers
115 views

Why inversion of wave for rope fixed at one end?

Setup: A rope is fixed at one end to a wall. You swing the other end up and down once. A wave starts travelling. It moves, hits the wall, then flattens, then is created again underneath (inversed), ...
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182 views

Two layers of glass reflection related to wave interference [closed]

A highly reflective mirror can be made for a particular wavelength at normal incidence by using two thin layers of transparent materials of indices of refraction $n1$ and $n2 (1 < n1<n2 ) $on ...
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1answer
44 views

Water wave packet variance

Consider the following quantity, $$I = \int x^2|\eta(x)|^2 \ dx,$$. For $\eta(x)$ a solution to some linear equation, we have $\eta(x) = \int a(k) e^{ikx} \ dk$ where, for $\eta$ to be real, we ...
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2answers
99 views

Is there a (cheap) optical resonance demonstration using visible light?

I'm looking for a impressive, inexpensive lecture demonstration of optical standing wave resonance. Preferably visible light. Can anyone suggest such a demo?
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0answers
110 views

Phase and group velocity of a soliton? [closed]

How do I find the phase velocity and group velocity of a soliton with a $\operatorname{sech}$ (hyperbolic secant) envelope?
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5answers
538 views

Isn't all light polarised?

I apologize if my question does not make sense.(I'm teaching myself microscopy.) So reading Fundamentals of Light Microscopy and electronic imaging by Douglas&Murphy, at one point the author ...
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1answer
363 views

Definition of “destructive” interference of waves

What is the commonly accepted precise definition of "destructive" interference of waves. Does it mean: interference with complete cancellation or interference where the amplitude gets smaller ...
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2answers
87 views

Importance of the $\exp (i \bar{k} \cdot \bar{r})$ part of the plane wave equation

I am having trouble grasping how the equation $\bar{E} \left( \bar{r}, t \right) = \bar{E}_{0} \exp \left[ i \left( \bar{k} \cdot \bar{r} - \omega t \right) \right]$ fully describes a plane wave. ...
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60 views

How do traffic waves travel downstream?

How do traffic waves travel downstream (traveling in the same direction as the flow of traffic)? i.e. How can the flow of traffic in a particular location be affected by the flow of traffic behind ...
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2answers
146 views

Drawing phasor diagrams when $x$ is the sum of two cosine terms

If $$x= A\cos(w t) + A\cos(W t),$$ how do I draw a phasor diagram when $t=2$? Do I treat each cosine term as a vector, and then do vector addition? I know I have to differentiate to get the ...
2
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1answer
145 views

polarization of a transverse wave travelling in ionosphere with polarization direction perpendicular to earths magnetic field

Assume a transverse electromagnetic wave entering ionosphere such that its Electric field of wave is perpendicular to earths magnetic field. Now, i read that as it will enter plasma, the wave will ...
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1answer
164 views

General solution to the wave equation of electromagnetic field

Suppose that we have the four-vector potential of the electromagnetic field, $$A^i$$ The wave equation is given by $$\Box A^i=\frac {\partial^2}{\partial x^k \partial x_k } A^i= \left(\frac {1}{c^2} ...
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1answer
141 views

How does a non-diffracting beam form from a converging ring of illumination?

I am trying to intuitively understand the basics of the supplementary text of a recent publication from Eric Betzig's group on lattice light sheet microscopy (1). I am confused by the explanation of ...
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2answers
184 views

What is the phase shift incurred by a sound wave as a result of reflection?

While studying waves I read the fact that a sound wave gets shifted by $\pi$ as a result of reflection against a surface. But I am unable to prove that fact. Assuming the interface to be a node I can ...
3
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1answer
225 views

How to create a barrier for sound waves?

Is there a way to create a barrier so that sound waves cannot pass through? Does laser light have this ability to act as a barrier or bounce sound waves back? This came to my mind when I was ...
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1answer
795 views

What influences the intensity of a wave? Frequency vs Amplitude

So, in school, I have been taught that $I$ is proportional to $A^2$. However, when I look at the equation $E = h\cdot f$, I see the frequency has an impact too on the intensity! Now, if a sound wave ...
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72 views

Electric Field Inside Dielectric Filled Cavity

I want to determine the electric and magnetic fields inside the following cavity: perfect conducting walls at $z = 0, z=d, x=0, x=b, y=t, -t^\prime$, with a dielectric $\epsilon$ filling ...
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3answers
290 views

Would this Produce Thrust? (Photon Momentum, Speed of a Pressure Wave)

This thought occurred to me after I began reading about the EM drive, and I know there are a lot of theories out there on how that works/doesn't work, I'm wondering why this solution wouldn't make ...
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2answers
244 views

Symbol in energy formula vs amplitude

Can someone tell me what does the symbol mean in the formula for energy compared to amplitude? Looks like a partial infinity sign, almost like a fish symbol.
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2answers
186 views

Polarisation definition

What is more correct and what is the difference? Polarised waves are waves with vibrations in one direction perpendicular to energy propagation "vibrations in one plane" "vibrations in one direction ...
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1answer
56 views

Tranverse electromagnetic waves

TEM waves do not exist in waveguide. Is this the correct explanation- Both curl and divergence of TEM are zero inside the waveguide and because of the boundary conditions (electric field zero at every ...
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4k views

Why frequency is inversely proportional to time-period?

Why frequency is inversely proportional to time-period? While studying about Fourier transform that shows frequency representation. A doubt that came to me was a set of signal with same wavelength ...
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1answer
162 views

Path Difference Due to Angled Incident Light

If light incident on a diffraction grating makes an angle $\alpha$ with respect to the normal to the grating, show how $$m \lambda = d\sin\theta$$ becomes $$m\lambda = d[\sin(\theta - \alpha) + ...