Questions tagged [electromagnetic-radiation]
Propagating solutions to Maxwell’s equations in classical electromagnetism and real photons in quantum electrodynamics. A superset of thermal-radiation.
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Are Transmission values for absorptive light filters proportional to Intensity?
Mostly filter rates are given in percent, but if I imagine that for example 10 photons hit an absorption filter with 50%, molecules are excited there and in the end only 5 get through while the other ...
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Interference of coherent electromagnetic waves in two dimensions?
Interference of two coherent but mutually perpendicular electromagnetic waves whose electric field vectors are given by
$$E_{1} =E_{0} \cos (\omega t) \widehat{i} $$
$$E_{2 } =E_{0} \cos (\omega t ...
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Is there a way to make infrared pass through metals?
I am curious to know a way that will make infrared pass through metals. Metals are good reflectors of infrared,can we manipulate the wave in order to make them pass through metals?.
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Can interference occur between two consecutively arranged light filters (via reflection) in the space between them?
(This is a follow up question from my previous one: Do the values of two reflective light filters arranged one behind the other add up in this way?)
The light of the imaginary intensity 1 is viewed ...
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Frequency of EMR vs clockspeed of a processor
I was recently reading this thread on Reddit where people discussed the implications of a "Terahertz processor", a computer processor that operates at a clockspeed of greater than 1 ...
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Confusion about energy transport in a circuit
I have some confusions about how to imagine energy flow in a circuit. Imagine for example just a simple circuit with a battery, two wires and a light bulb.
According to classical Electrodynamics the ...
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Why is the stress-energy tensor for electromagnetic radiation traceless?
A photon gas obeys the equation of state $\rho=P/3$ and hence $T^{\mu}_{\quad\mu}=3P-\rho=0$.
(Can also be seen by expressing the stress energy tensor in terms of of the electromagnetic tensor as ...
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Geometrical and wave physical effects
Is it right to say diffraction is a geometrical optics phenomena and scattering a wave physical effect? I am considering a finite-length conducting plane and supposing a wave hitting the surface and ...
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What effect does color on the upper and lower side of umbrella have?
This question isn't referring to the general use of umbrella to provide protection from rain rather it concerns the optical effects of the color on lower and upper portion of umbrella.
Umbrella are ...
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Why do small particles deferentially scatter colors (i.e scatter more blue light than red in Rayleigh scattering) while larger particles don't?
In both small and large particles, light as an EM wave will accelerate charged particles such as electrons and induce a dipole forcing the electrons to oscillate at the same frequency of incident ...
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Why is it called a "black" body?
So i know a black body is a perfect absorber and perfect emitter.. doesnt have to be black, but why is the term "black" used. In my textbook, it says that "at lower temperatures a ...
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Do photons make the universe expand?
I have a problem understanding the ideas behind a basic assumption of cosmology. The Friedmann equations follow from Newtonian mechanics and conservation of Energy-momentum $(E_{kin}+E_{pot}=E_{tot})$ ...
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When exactly does a change in $E$ or $B$ result in an electromagnetic wave?
I am always wondering why only accelerated charges emit electromagnetic waves, while constantly moving ones do not.
I imagine an electron in else empty space moving with speed $v$. The $E$-Field in a ...
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Ratio between conduction current and displacement current
First, recall that the Maxwell displacement current for a plane wave is
$$ \vec{\jmath}_D = \epsilon\partial_t \vec{E} = \epsilon\partial_t \left[\vec{E}_{0} \cos\left(\vec{k} \cdot \vec{r} - \omega t\...
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How can we prove for magnification of an astronomical telescope?
It is known that when we increase the length of the tube of an astronomical telescope the magnifying power decreases, how do we prove it?
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Gravitational convergence of light
light has a non-zero energy-stress tensor, so a flux of radiation will slightly affect curvature of spacetime
Question: assume a flux of radiation in the $z$ direction, in flat Minkowski space it ...
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What is the smallest possible wavelength? [duplicate]
I was thinking about this the other day after a quantum mechanics lecture (unrelated to the lecture I was taking) and pondered "Is there a minimum wavelength for a photon?", through ...
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Can the temperature of a body become lower than the temperature of the surrounding air?
In winters, frost is formed on the grass and wood and not on concrete roads.Temperature of frost is lower than the temperature of the surrounding air.So a question arises ""Can a body become ...
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How does Planck's Constant solve the ultraviolet catastrophe?
I am studying black body radiation and a high school level for a class. My understanding of it is this:
There is a finite frequency light and therefore amount of ultraviolet light objects can emit. ...
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Reflection at a conducting surface
The boundary conditions that we used to analyse reflection and refraction at the interface between two surfaces are:
$\epsilon_1 E_1^\perp + \epsilon_2 E_2^\perp = \sigma_f$ where $\sigma_f $ is the ...
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Finding angles of second and third order minima given only angle of first order minimum
For the following problem we are asked to find the second and third order minimums of a single slit diffraction experiment at $13^{\circ}$. I tried using the following $$\theta_p=p\cdot\frac{\lambda}{...
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The radiation power of an electromagnetic wave scatter due to the magnetic field
In studying the scattering of an electromagnetic wave by a single charge, it seems typically we consider the motion driven only by the electric field, as is presented in Section 32-5 Scattering of ...
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Quantum mechanical description of a photon arriving at a telescope from extremely far away
Typically, telescopes are explained in terms of bouncing light paths around. For example, this image from wikipedia shows "photon tracks" being redirected:
I realize this is a very ...
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Can the time varying Intensity of an electric field of a wave be measured?
Lets say that we have a detector which we use to measure the intensity. Theoretically, the intensity is a varying function of time (When we calculate the Poynting vector) but often in textbooks they ...
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Understanding and inverting Kirchhoff's integral for the diffraction theory
The Kirchhoff diffraction integral has been discussed in the science society pretty often and appears to be a non consistent theory.
Never the less it's applicable and "gives" great results. Kirchhoff'...
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Why does light travel in a straight line if the uncertainty principle is true?
I've asked this on different websites and never gotten an answer that a layperson can understand. Most people just say that light does not have a trajectory and then they do some hand waving. If light ...
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$\rm Lux$ to $\rm W/m^2$ conversion?
For a physics project, I'm planning to investigate the relationship between the number of slits in a diffraction grating and the intensity of the central maxima. The light meter which I'm planning to ...
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How can radiation be a transverse wave? Does light really resemble a rope? How can a 3D field be a medium for non-spatial 1D waves? Need mental model
I understand longitudinal waves. For example, I've got a clear mental modal of air waves: a slice of air becomes overcompressed, then the slice next to it becomes overcompressed and the first slice ...
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Diffraction limit PSF and angular spectrum method?
I know from the angular spectrum method that given a field $U$ with a wavelength $\lambda$, we can decompose it with Fourier transform.
\begin{equation}
U(x, y,0) = \int \int {\tilde{U}_0(f_x,f_y)} ...
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Does energy conservation law conflict with Active Noise Cancellation
Assume the picture below:
From inlet port In1 and In2 we can have electromagnetic or acoustic energy entrace single sine wave with same amplitude and frequency. Assume we have aligned the waves to ...
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Light, Work, and the 2nd Law
I am trying to figure out what restrictions there are on converting light energy into work.
I understand that solar energy can be converted to electrical energy with roughly 90% Carnot efficiency. ...
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Michelson interferometer: beam splitter affects amplituedes?
Let's suppose an initial plane wave $\vec{E}=\vec{E_0}e^{i(\vec{k}\cdot\vec{r}-\omega t)}$ enters a Michelson interferometer . Let $\vec{E_1}=\vec{E_{01}}e^{i(kz-\omega t)}$ and $\vec{E_2}=\vec{E_{02}}...
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Relativistic Effects on Electromagnetic Wave Propagation
So for a recent lab I had to calculate the length of a conductor by measuring the time it took a signal to reflect off of the open end. I used the very simple principle of $v=st$ and, knowing that the ...
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How does Hertz's radio wave experiment show there are both magnetic and electric fields in a radio wave?
Could somebody check whether my understanding of this experiment is correct, because I feel like I assume Maxwell's results.
When a spark forms across gap, a spark is also created across the ...
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What happens in a conductor when the electric field has a plasma frequency?
The complex index of refraction for a conductor is given by the equation: $$N(\omega)=n+ik=\sqrt{1- \frac{\omega_p^2}{\omega^2+i\gamma\omega}} $$ where $\omega_p^2=Nq_e/\epsilon_0m_e$ is the plasma ...
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Why does an charge free space always create an oscillating field?
My question is on the nature of oscillating electric field. From Maxwells equation, we know that the solution of the electric and magnetic field for an empty space are always oscillating fields. I ...
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Thomson Scattering when low intensity light meets an orbital electron
Can you explain to me the reason why Thomson Scattering can not explain what happens when light meets an electron at low intensity, and what does that have to do with light being a wave or particle or ...
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A plane electromagnetic wave - phase change - amplitude
A plane electromagnetic wave has the shape:
$\vec{E}(\vec{r},t)=E_0\cdot cos(\vec{k}\vec{r}-\omega t)\cdot \vec{e}_y$
$\vec{B}(\vec{r},t)=(B_1\cdot cos(\vec{k}\vec{r}-\omega t)+B_2\cdot sin(\vec{k}\...
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Spontaneous emission as dissipation and fluctuation
Suppose we have some sort of medium and we want to build an effective theory of light inside. Of course we want to calculation the dielectric constant, which in turn is determined by the ...
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Poisson spot amplitude
The equation
$$
U(P) \propto \int_0^{2\pi} \int_0^{\infty} g(\rho,\theta) \exp\left[ \frac{i\pi}{\lambda}\left(\frac{1}{z_0} + \frac{1}{z_1}\right) \rho^2 \right] \rho \, d\rho \, d\theta
$$
or the ...
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Laser induced explosion (detonation)
I have a question involving quite the wacky (and silly) hypothetical. It's a part of an ongoing argument I'd like to settle. Of course, I have no background in physics which is why I came here, so I ...
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Question regarding synthetic UV sources (fluorescent, LED) and claims to "match the sun"
I am involved with some discussion regarding lamps specifically in use for reptiles. Captive reptiles can often suffer from hyperparathyroidism from a lack of vitamin D. The safest way found to ...
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How do i calculate change of momentum when I send a photon in the direction of travel
Say a spaceship is traveling at a certain velocity v (>>c) and it emits light from the nose of my spaceship in the direction of travel. The speed of light is finite and hence there should be a ...
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What is the potential energy of electromagnetic waves traveling in air?
The Lagrangian for electromagnetic waves shows that its energy has a kinetic part as well as a potential part (just like everything else). The potential part only exists in a medium whereas in the ...
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How exactly are incident EM waves cancelled by a conductor, and why only on one side of it?
This answer describes why EM waves from inside a microwave are blocked by the metal mesh screen:
The incident EM wave induces oscillations in the metal of the screen, and these oscillations reradiate ...
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Tangential component of the "electric" vector spherical harmonic $N_{lm} = \nabla \times (h X_{lm})$?
So I want to solve the problem of an electromagnetic plane wave scattering by a sphere myself, and one of the crucial steps is to solve the scattering of a converging TE- or TM-polarized vector ...
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Interpretation of watts per square meter for intensity of radiation
The energy that an electromagnetic field can deliver to a system is proportional to the square of the field. However, we use the terminology watts per meter square to represent the amount of energy ...
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Photon emission rate frequency dependency
I am puzzling over the dependence of the energy flux of electromagnetic radiation on the frequency of the source.
The power radiated in any direction or solid angle from a charged particle ...
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How Are Electromagnetic Waves Produced?
How EM waves are produced say by a capacitor of an LC circuit here if $E$ is increasing in upward direction?
My thoughts
Thought 1:-
If E is increasing E flux is increasing thus B field must be ...
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From the physics standpoint, how should I align a USB Internet stick relative to the nearest cell tower in order to have the best signal? [closed]
I use this USB Internet stick:
(Huawei E3372h-153)
To connect to the Internet, I simply insert a SIM card into this stick and then insert the stick into a USB port of my laptop.
Based on my ...
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