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.
5
votes
1answer
103 views
How is it possible for an Ultrasound device to correctly interpret a negative density change in tissue?
I understand the principles of Ultrasound Imaging, and the mathematics behind sonar velocity, impedance, and reflection.
I also understand that an Ultrasound device recieves an echo produced by ...
5
votes
1answer
210 views
Meaning of negative frequency of sound wave
Suppose that Alice and Bob are both holding speakers emitting sound at a frequency $f$. Alice is stationary while Bob is moving towards Alice at twice the speed of sound.
In the case of Alice, if I ...
5
votes
5answers
1k views
Why no longitudinal electromagnetic waves?
According to wikipedia and other sources, there are no longitudinal electromagnetic waves in free space. I'm wondering why not.
Consider an oscillating charged particle as a source of EM waves. Say ...
5
votes
2answers
1k views
What allows the Wave Disk Generator to be so efficient?
Researchers at Michigan State University recently invented the Wave Disk Generator that is supposed to get 60% fuel efficiency. What allows it to be so much more efficient than a traditional Internal ...
5
votes
2answers
269 views
Will a wave packet undergo dispersion when traveling down a hanging rope?
Suppose I tie one end of a rope to my ceiling and the other end to a spot on my floor directly underneath it. Because the rope has some mass, the tension varies along the rope, from highest at the ...
4
votes
4answers
545 views
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 ...
4
votes
2answers
176 views
Does a finite wave necessarily have to be non-monochromatic in reality?
Does a finite wave necessarily have to be non-monochromatic in reality, or is that implication just a result of the mathematical analysis? I always wonder at these sort of things that come out of a ...
4
votes
2answers
176 views
Are there “gaps” in light, or will it hit everywhere?
Not sure how to word my question.
Picture a light source in vacuum, so nothing disturbs the light (or similar conditions), 2d.
If I move very, very far away, will it happen that some of the light ...
4
votes
4answers
417 views
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?
...
4
votes
3answers
348 views
Physics of a guitar
I understand that when you pluck a guitar string, then a bunch of harmonic frequencies are produced rather than just the frequency of the desired note.
If this is true, why does C2 sound so different ...
4
votes
1answer
491 views
The speed of sound is proportional to the square root of absolute temperature. What happens at extremely high temperatures?
The speed cannot increase unboundedly of course, so what happens?
4
votes
1answer
241 views
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 ...
4
votes
1answer
100 views
Normal modes of a flexible rod clamped at only one point
I am interested in the vibrations of a thin, flexible rod that would only be clamped at one point, properly I'd like to calculate its eigenvalue. But the way I learned it in wave mechanics doesn't ...
4
votes
3answers
184 views
Are two waves being in phase is the same as saying that the two waves are coherent?
If two waves are coherent, is it the same as them being in phase? Please correct if I'm wrong.
4
votes
1answer
75 views
The Effects of Moving Matter Across Light-Year distances
If I were to stand at one end of a light-year long metal pole, and another person were to stand one light-year away at the other end, and then I were to push on my end of the pole. How long would it ...
4
votes
2answers
1k views
Physical interpretation of Parseval's theorem
I have read that Parseval's theorem, relating the norm of a function $f$ and the norm of its Fourier transform $g(k)$:
\begin{equation}
\int |f(x)|^2 dx=\int|g(k)|^2 dk
\end{equation}
has the ...
4
votes
1answer
137 views
Why do rain waves form and what is their connection to the texture of the surface they're on?
When it rains and water flows down an inclined street, ripples may form that are carried along with the current. Here's a picture with an example of what I'm talking about
I'd like to know what the ...
4
votes
2answers
302 views
Interference of EM Waves with Orbital Angular Momentum
If you have two coherent collinear e-m beams of same frequency and polarization, but 180 degrees out of phase, they will destructively interfere.
If you introduce orbital angular momentum of L=3 ...
4
votes
1answer
187 views
1D Wave mechanics (string)
Suppose I have a wave traveling to the right described by $e^{iw(t-{x\over c})}$. (It obeys the 1D wave equation). AND at $x=0$, there is a mass $M$ fixed to the string such that we have $M{d^2y\over ...
4
votes
0answers
52 views
What's the difference between exchange spin wave and magnetostatic spin wave?
So far I've heard of three kinds of spin waves
Magnetostatic spin waves (MSW)
Dipole-exchange spin waves (DESW)
Exchange spin waves (ESW)
What's the difference?
4
votes
0answers
297 views
Hankel function in terms of planewaves [closed]
It is well know that planewaves are a complete basis for solutions to the wave equation. Let us assume a 2D space, and at fixed temporal frequency, the equation reduces to the Helmholtz equation. In ...
3
votes
4answers
1k views
How can a sine wave represent a longitudinal wave?
I envision a longitudinal wave as a series of vertical lines like that drawn on the board in an introductory physics class. This image contains no angles. Sound is a longitudinal wave.
Some ...
3
votes
2answers
195 views
Can someone explain how water from a garden hose can propagate in a sine/cosine wave?
A video posted on Youtube : http://www.youtube.com/watch?feature=player_embedded&v=uENITui5_jU
How does this phenomenon work? I know he is using frequency to propagate water in a sine/cosine ...
3
votes
2answers
3k views
Do light and sound waves have mass
I have been reading Hawking's 'A Brief History of Time' and it has gotten me thinking about Einstein's theory of relativity, in that it assumes that an object must have infinite mass if it is to be ...
3
votes
2answers
1k views
How is the speed of light calculated?
How is the speed of light calculated? My knowledge of physics is limited to how much I studied till high school. One way that comes to my mind is: if we throw light from one point to another (of known ...
3
votes
3answers
206 views
Knowing when wavefunction collapses
So I learned that after a measurement of, lets say the position of the wavefunction of a particle is made, if another measurement of the position of the particle is made right away, you should get the ...
3
votes
1answer
158 views
Does $\lambda\nu = c$ hold for all the waves in the universe?
Are all waves in the universe the same as electromagnetic waves?
Basically, my question arises from an equation I found in my chemistry textbook:
$$\lambda \nu ~=~ c.$$
This states that the ...
3
votes
2answers
945 views
The energy of an electromagnetic wave
The intensity of an electromagnetic wave is only related to its amplitude $E^2$ and not its frequency. A photon has the same wavelength as the wave that's carrying it, and its energy is $h f$.
So ...
3
votes
2answers
255 views
Do non-metal objects reduce the signal strength of a computer wireless network device?
Would an object like a wooden bed interfere or block the signal coming from a 802.11 wireless router?
3
votes
2answers
81 views
Is there a way to create a flickering frequency to be dependent on speed of the person looking at it?
Is there a way to make a screen or a road sign flash at different rates, depending on the velocity of the observer looking at it?
I would like to achieve a state where two observers going at ...
3
votes
2answers
587 views
How do mirrors work?
Apparently, light is just a certain wavelength, or "the visible spectrum" of electromagnetic waves. If I recall correctly, my physics teacher explained to me that electromagnetic waves are basically ...
3
votes
2answers
636 views
How can sound waves propagate through air?
We know that the sound waves propagate through air, and it can't travel through vacuum. so the thing that help it doing that is the air's molecules pressure. So my question how can that happens? I ...
3
votes
1answer
336 views
How does a speaker produced different sounds?
What I have read is that a speaker produce sound by just moving a coil attached to a cone which moves back and forth. So, If I try to move the coil by hand, would it produce sound? If not why not? or ...
3
votes
1answer
113 views
What is it that undulates in a particle?
When there is a wave, something is undulating. In the example of a rope, the rope is what undulates. In the case of a ripple on a pond, the water is undulating, and when a sound wave propagates, the ...
3
votes
1answer
46 views
Boundary conditions on wave equation
I am having trouble understanding the boundary conditions.
From the solutions, the first is that $D_1(0, t) = D_2(0, t)$ because the rope can't break at the junction.
The second is that ...
3
votes
2answers
337 views
Energy in an EM wave should depend on frequency
I just finished reading Feynman's Lectures on Physics vol.I, §34-9: "The momentum of light". The author explains that there is a relation between the wave 4-vector $k^{\mu}$ and the energy-momentum ...
3
votes
2answers
209 views
Waveguide and ethernet
I am having a doubt about waveguides and the traditional Ethernet cable.
The newest Ethernet i.e. the 10Gbps Ethernet has an astounding speed of 10Gbps. Which consists of 4 lanes in Cu as physical ...
3
votes
1answer
728 views
Light waves and Schrödinger probability waves
Ok, bearing in mind that I only have a brief understanding of quantum mechanics (no formal education, only from reading about concepts in books), so I could be way off here, I have a question ...
3
votes
1answer
76 views
Why do sound waves travel at the same speed moleculewise? (Same medium)
I don't understand what happens in reality (outside of wave theories). If I clap my hands I invest energy in the nearby air molecules, which move and transfer their energy to nearby molecules which ...
3
votes
1answer
42 views
References on wave solutions in continuum mechanics [closed]
I am interested in literature on known wave solutions in continnum mechanics, precisely the following mechanical equation:
$$\rho\partial_t^2u_i = C_{ijkl}\nabla_j\nabla_ku_{l}$$
My interest is spread ...
3
votes
2answers
279 views
Matter waves - DeBroglie's relations
I am currently studying from Modern Physics for Scientists and Engineers by Taylor et al. They derive the DeBroglie relation $p=h/\lambda$ from setting mass $m=0$ in the energy-momentum relation ...
3
votes
1answer
121 views
Earthquake as a transverse wave
I have a very simple mental picture that earthquake waves travel like shear (transverse) waves through the earth.
a. Does the speed of this wave give any valuable information about the mechanical ...
3
votes
2answers
176 views
Simple PDE vs String Theory
For the sake of simplicity, I’d like to believe that there is one master non-linear partial differential equation
governing physics. In particular, consider a Klein-Gordon form:
$$
\frac{\partial^2 ...
3
votes
2answers
890 views
why is mechanical waves faster in denser medium while EM waves slower?
Why is it that mechanical waves/longitudinal waves/sound travel faster in a denser/stiffer medium as in steel compared to say air, while EM waves/trasverse waves/light travels slower in a (optically) ...
3
votes
3answers
2k views
Why is energy in a wave proportional to amplitude squared
I'm a mathematics student trying to grasp some basics about wave propagation. A sentence I find very often in introductive physics textbooks is the following:
In a wave, energy is proportional to ...
3
votes
1answer
121 views
Wave equation for sound waves and moving source
Is there a way to take a moving source already into account when one derives the wave equation for sound waves and derive from that using only math the Doppler effect for moving sources?
3
votes
2answers
321 views
What is the dominant cause for ocean waves at a beach?
What is the dominant cause for ocean waves at a beach? Are they the result of wind/pressure difference? If so, the waves do seem to exist in similar intensity even during relative quiet times of the ...
3
votes
1answer
532 views
Phase and Group Velocity of Electromagnetic Waves
Moving charges produce oscillating electric and magnetic fields -we have an electromagnetic wave.
In terms of moving charges or at the level of charges, what is phase velocity and group velocity of ...
3
votes
1answer
146 views
Electric field Fourier decomposition
I have the following decomposition for the electric component of light:
$$\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 ...
3
votes
1answer
71 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 ...
