Tagged Questions
-2
votes
0answers
73 views
Velocity, Wave Equation, Differential Equations [closed]
Suppose you have a differential equation of the form:
$$
\frac{\partial^2 u}{\partial z^2} = C \frac{\partial^2 u}{\partial t^2} + D \frac{\partial u}{\partial t}$$
Is it possible to find the ...
0
votes
1answer
33 views
Phasor representation of voltage in frequency domain
In a text on application of electromagnetism in transmission line, there introduces a phasor for the voltage (in frequency domain)
$$\tilde{V}(x) = V^+e^{-i\beta x} + V^-e^{i\beta x.}$$
Here $V^+$ ...
-1
votes
1answer
54 views
EM Waves Energy Loss
Where does the energy go when two photons interfere destructively at a point on a screen in Young's double slit experiment ?
1
vote
0answers
52 views
Fourier Transform of ribbon's beam Electric Field
I have a monochromatic ribbon beam with $E(x)e^{i(kz-\omega t)}$ being the electric field's amplitude. I want to show that the lowest order approximation in terms of plane waves is
...
1
vote
1answer
69 views
Power radiated by the sun at different locations
I am wondering can someone help to solve second part which extends first part;
The power radiated by the sun is ${3.9*10^{26}}_{watt}$. The earth orbits the sun in a nearly circular orbit of radius ...
0
votes
1answer
141 views
Eddy current losses in electric steel by harmonics of a magnetic field
I am working on an model of a permanent magnet synchronous machine. Right now I am stuck with calculating the eddy current losses caused by the harmonics of the stator magnetic field in the electrical ...
0
votes
1answer
55 views
what is the difference between constant and changing magnetic and electric fields? How do they occur? How do they form an electromagnetic wave?
what is the difference between constant and changing magnetic and electric fields? How do they occur?
How do they form an electromagnetic wave?
2
votes
2answers
262 views
Why are AC quantities represented by sine waves always?
Usually we use a sinusoidal wave form to represent a alternating quantity. Why not a cosinusoidal wave or a ramp wave form?
In sine wave forms we can indicate the maximum and minimum amplitude and ...
0
votes
0answers
71 views
How to get electromagnetic wave from transmitted power?
If a question states that a transmitter emits 90W power, is it meant as average power density or Poynting vector magnitude?
Is it somehow possible to deduce E(z;t) and H(z;t) from it?
Electric ...
0
votes
0answers
42 views
EM-wave hits a brick-wall, $\pi/2$ -phase-shift? [duplicate]
Possible Duplicate:
Phase shift of 180 degrees on reflection from optically denser medium
If I have a cord-wave, I get a phase-shift with attached cord but do I get such a phase-shift with ...
0
votes
1answer
91 views
Wavefronts and phase velocity faster than $c$
Lets assume we have parallel wavefronts in a glass of water:
and we put an inclined rod on the water surface:
related to a very small inclining, Vy velocity is greater or much greater then Vx ...
2
votes
2answers
110 views
What is the history behind the factors of 3 in the classification of electromagnetic radiation?
What is the history behind the factors of 3 in the classification of electromagnetic radiation?
See e.g. http://en.wikipedia.org/wiki/Radio_spectrum#By_frequency
Is this (just) inherited from the ...
3
votes
2answers
639 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 ...
7
votes
3answers
3k views
Phase shift of 180 degrees on reflection from optically 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 it ...
-1
votes
2answers
187 views
Why do you get electric field of a light wave?
Why do you get electric field of a light wave in following form: $E(x,t)=A cos(kx-\omega t- \theta)$?( look at: https://public.me.com/ricktrebino -> OpticsI-02-Waves-Fields.ppt, p. 18)
1
vote
1answer
127 views
Relationship between gauss and decibels
In my ongoing effort to understand the world around me, I want to wrap my head around the relationships between two units of measure. Specifically gauss and decibels.
The quandary comes from my ...
9
votes
5answers
534 views
Superposition of electromagnetic waves
The superposition of two waves is given by
$$\sin(\omega_1 t)+\sin(\omega_2 t)=2\cos\left(\frac{\omega_1-\omega_2}{2}t\right)\sin\left(\frac{\omega_1+\omega_2}{2}t\right).$$
For sound waves, this ...
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 ...
1
vote
1answer
289 views
Is there orbital angular momentum for all particles?
Light as an electromagnetic wave can be polarized in different ways, e.g. linear or circular. As far as I understand it currently this can be compared to the spin direction of a propagation electron ...
3
votes
1answer
152 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 ...
0
votes
0answers
113 views
What is the electric field part of an EM wave? Radiation field or the induction field?
Look at this image:
I wonder if the electric field is from the induction field from a vibrating electron or the radiation field? If it is from the radiation field, as I suppose, than can someone ...
2
votes
3answers
460 views
Electromagnetic wave reflection vs. light reflection
Related: x-ray interaction with atmosphere
I know that electromagnetic waves of particular frequencies reflect from the ionosphere. And the light (which from one perspective is an electromagnetic ...
3
votes
2answers
358 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 ...
1
vote
1answer
806 views
Relation between wavenumber and propagation constant
What is the exact difference between wavenumber and propagation constant in an electromagnetic wave propagating in a medium such as a transmission line, cause i am a bit confused. Does it have to do ...
2
votes
1answer
73 views
Close electric field lines in wave guides
In a wave guide, graphics of propagation of Transversal Magnetic modes show closed field lines for the electric field.
For example, for a rectangular guide:
$E_x (x,y,z) = \frac {-j\beta m \pi}{a ...
3
votes
1answer
70 views
How does one determine whether an object will make an EM wave refract in a qualitative way?
for example, i have a vague notion that the actual answer is that the permittivity and permisivity are different in each different material, so all waves refract at every boundary, but we only call it ...
2
votes
1answer
224 views
Counting the number of modes
The exercise is the following
Show that the number $N(\lambda) \, \mathrm d \lambda$ of standing electromagnetic waves (modes) in a large cube of volume $V$ with wavelengts within the interval ...
0
votes
2answers
325 views
Why is Polarization of a wave important, and what happens when a wave is polarized in all three dimensions?
I don't quite understand this, I understand that given a wave traveling in a certain direction, it will be polarized in the direction its not travelling in, so if its travelling in the Z direction, k ...
2
votes
2answers
367 views
Does space have to be filled with charged particles to carry electromagnetic waves?
I'm a newbie here so have mercy.
I'm studying electromagnetic waves. This is the propagation of energy via the vibration of charged particles, as I understand it.
A charged particle could be like ...
4
votes
2answers
305 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 ...
0
votes
1answer
484 views
Changing magnetic flux graph?
In regards to a graph of the changing magnetic flux in a generator such as this one:
a) The equation of the graph should be $\Phi = BA \cos \theta$. As $\theta=\omega t$ (angular velocity*time), ...
1
vote
0answers
120 views
Reflected electromagnetic wave relation
If incident electromagnetic wave is given as:
$$\begin{align*}E_i&=A_e \cos(\omega t + bz)\\
H_i&=A_h \cos(\omega t + bz)\end{align*}$$
What would be relation for REFLECTED wave?
Does it ...
6
votes
2answers
163 views
Multiple channels of information in single electromagnetic wave?
I'm trying to understand how can multiple radio stations transmit information just by transmitting using different frequency. The way I understand it all those different frequency waves add up to a ...
3
votes
1answer
242 views
Lorentz invariance of a frequency- and wavelength- dependent dielectric tensor
Suppose we have a material described by a dielectric tensor $\bar{\epsilon}$. In frequency domain, this tensor depends on the wave frequency $\omega$ and the wave vector $\vec{k}$.
Clearly not all ...
5
votes
5answers
801 views
Why aren't there compression waves in electromagnetic fields?
I just started learning about optics, and in the book I'm reading they explain how the electrical field caused by a single charged particle could be described by a series of field lines, and compare ...
7
votes
5answers
882 views
Why don't waves erase out each other when looking onto a wall?
If I stand exactly in front of a colorful wall, I imagine the light waves they emit, and they receive should randomly double or erase out each other.
So as a result, I imagine I should see a weird ...
1
vote
1answer
485 views
How radio waves penetrate through buildings?
For example how radio signals of a base transceiver station (BTS) penetrate through buildings?
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 ...
8
votes
2answers
936 views
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 ...
2
votes
3answers
875 views
How is electromagnetic wave variation distributed in space?
Imagine an electromagnetic wave (a monochromatic one for example)
The electric field amplitude, and its variations travel in the propagation direction.
So, if there really exists a propagation ...
1
vote
2answers
154 views
EM irradiament and multipoles
Why in the irradiament mulipoles of Lienard-Wiechert's potential we say that electric quadrupole give a contribute of the same order of the magnetic dipole? How can we see it from their equations? And ...
6
votes
3answers
277 views
Controllable faster-than-light phase velocity
This is not another question about faster-than-light travel or superluminal communication. I totally appreciate the speed limit capped by physical laws (or theories.)
Just curious, since there is no ...
1
vote
2answers
219 views
Creation of the Electromagnetic Spectrum [closed]
After seeing this image:
http://mynasadata.larc.nasa.gov/images/EM_Spectrum3-new.jpg
And reading this:
"The long wavelength limit is the size of the universe itself, while it is thought that the ...
2
votes
2answers
141 views
Utility of displacements potentials in geophysics
In the elasticity theory, you can derive a wave equation from the fundamental equation of motion for an elastic linear homogeneous isotropic medium:
$\rho \partial^2_t \overline{u} = \mu \nabla^2 ...
