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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Question about unit for intensity
The picture is from one physics textbook about treating sun as a blackbody and compare the electromagnetic radiation spectrum. Note the unit used for Intensity in the picture shown, it's Watts / (...
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Why are there hemispheres in Huygens principle?
In the formulation of Huygens principle, it is said that the secondary waves are spheres but on the plots for determination of the wavefront there suddenly become hemispheres? What is the reason for ...
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Is laser light a standing wave?
If I understand it correctly the light waves are standing within the laser cavity as they bounce off the walls. Does that mean they remain standing as they leave the cavity? There is nothing out there ...
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Refractive index of water
The index of refraction is given by the following formula:
$$
n = \sqrt{\frac{\epsilon \mu}{\epsilon_0 \mu_0}} = \sqrt{\epsilon_r \mu_r},$$
where $\epsilon_r$ is the relative permittivity/dielectric ...
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1-Dimensional Frequency Density Diagram along axis $n$ and distance?
I was reading Resnick and Eiseberg's Quantum Mechanics in conjuction to watching this video on the UV catastrophe : https://www.youtube.com/watch?v=rCfPQLVzus4&t=1206s&ab_channel=...
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Are electric field lines always perpendicular to a conductor's surface?
I know that in a conductor body, in an electrostatic situation (Where $\vec E=0$ in the interior), the E field must be perpendicular to the surface outside because it is solely generated by electric ...
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Why is the electric field on the surface of a perfect conductor zero when an electromagnetic wave hits it? [duplicate]
I am studying electromagnetic waves, and in many texts it is stated that when a plane wave hits the surface of a perfect conductor, the electric field must be zero in the surface and inside the body. ...
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Microwave interference inside a leaking Faraday Cage
Let's consider a perfect cubic Faraday-cage with solid metal walls of several centimeters' thickness. Radio waves from the microwave region are fully blocked by this cage, and the fieldstrength inside ...
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Excitation and acceleration of charges is the only way to produce EM radiation?
In lasers electrons are excited, in free-electron lasers electrons are periodically accelerated as well as in radio antennas. Radiation is produced when deflected in a magnetic field. Thermal ...
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Virtual photons and slowing down longitudinal wave propagation
It is often described, that virtual photons are mere mathematical constructs, that can turn to real photons if there is enough time and space. And also, that virtual photons can mediate longitudinal ...
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Book recommendation on interference with relativistic treatment
I'm looking for a book that treats the propagation of EM waves in a medium with an index of refraction $n(x)$, with the idea of looking for the interference caused by two light rays that travel along ...
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Is the concept of the emission of photons applicable to radio waves? [duplicate]
I know that the emission of photons occurs when electrons are accelerated or deflected.
Since electrons are also accelerated in antenna rods, the concept of photon emission should also be applicable ...
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X-rays during the generation of long-wave radiation [closed]
When generating long-wave radio radiation, do not stand next to the antenna mast, as X-rays are present here. The same applies to radars, which also generate X-rays. How is this unwanted radiation ...
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Why does the area close to a charged particle move at the exact speed as the particle itself? [closed]
when a charged particle moves the area around it moves at the same speed as the particle itself so if the particle had a velocity of 10m/s down then the electric waves at a 10m radius around it moves ...
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How many alpha and gamma rays are given off from nuclear waste uranium 235
From the products of uranium 235 waste how much total energy / beta, alpha, gamma rays would be emitted from the decay of uranium 235 over its time of decay.
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$Q$ Transfer via Radiation Formula
According to the formula:
$$
\frac{\Delta Q}{\Delta t}=\sigma\epsilon A T^4
$$
What does $T$ refer to in a situation where I am modelling the power of radiation from air of temperature to surface of ...
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Why does high frequency have high energy?
The electromagnetic spectrum's wavelengths all travel at the same speed, $c$. Also, the wavelength $\lambda$ and frequency $\nu$ are related by $c = \lambda \cdot \nu$. Since all moving particles here ...
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Does a radio receiver "collapse" a radio wave function?
Does a radio receiver "collapse" a wave function when listening to a radio broadcast generated via a transmitting antenna?
Background:
There has been much discussion on this forum (here) ...
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Do all objects at the same temperature glow the same color?
Does Kirchhoff's law for heat radiation imply that all objects at the same temperature will glow the same color?
In other words, if a piece of molten iron glows the same color as my body, which ...
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What does the electromagnetic wave of a photon do?
So for example in the double slit experiment, you can see the interference pattern on they screen of where the photons hit it. That makes sense to me. What doesn’t is that since in this simulation, if ...
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Right hand and left hand orientation for electromagnetic waves
An EM wave has an electric and a magnetic field component and in a vacuum both are perpendicular to each other. As you can see from the Wikipedia sketches and my scribbles, the waves in the pictures ...
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How does a scintillator work? [duplicate]
I am trying to understand how a scintillator works.
Currently my understanding is this:
gamma radiation interacts with atom A (through photoelectric absorption or compton scatter) which produces a ...
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Penetration of electromagnetic waves in insulators?
The exact formula for the attenuation of E&M waves in a conducting material can easily be found in most textbooks on applied E&M.
I am wondering if such a equation (approximation or not) ...
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Why there can't be an isotropic radiator?
Why there can't be an isotropic radiator? I know you can prove it using Maxwell's equations but I don't see how.
Can someone please help?
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Why is a receiving antenna optimal at $\frac{\lambda}{2}$, mathematically?
I can understand the qualitative argument of a recieving antenna becoming resonant: An external $E$-field causes the charges to move in a conductor and bunch up, creating a voltage. If the driving $E$-...
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Why terms proportional to derivative of EM $A_\mu$ field do not explicitly appear in the Dirac Eq?
In Dirac Eq in presence of EM field we normally include the minimal coupling based on $U(1)$ symmetry argument, as $$\gamma_\mu (\partial_\mu +\frac{ie}{\hbar c} A_\mu) + \frac{mc}{\hbar}.$$ Now I am ...
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Is stimulated emission emitted by a rotating classical dipole subject to a resonant oscillating wave beamed?
Consider a dipole, $\pm q$ connected by a rigid rod of length $2L$, spinning around its center in the $x-y$ plane with angular frequency $\omega$, such that the charges follow $\vec{r}_{\pm q}(t) = \...
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Can a rotating charged carrying sphere act as a disco ball?
So, basically a resting charge has an electric field, a moving charge has a magnetic field while an accelerating charge emmits a electromagnetic waves.
There is a relation between the frequency of ...
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Why was there a need to create the ether when we knew the existance of magnetic fields? [closed]
I have been reading about 19th century physics and how it was believed that electromagnetic waves needed a medium in which they traveled at c, my question is why was it thought that the ether needed ...
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In double-slit experiment, do photon go thorough slits symmetrically? (Wave length is one 1000th of the slits distance.)
I understand the way double-slit is shown and ridges pattern calculated (e.g. https://personal.math.ubc.ca/~cass/courses/m309-03a/m309-projects/fun/Slits.html#topic1) is by assuming two identical ...
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In double-slit experiment, if one directs coherent light from two sources into each slit separetely, is ridges pattern expected to be seen?
I've read several QA here:
Is coherent light required for interference in Young's double slit experiment?
Why can't we duplicate the double slit experiment with two parrallel sources of light.....
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How EM radiation propagates? [closed]
The following is my understanding of how electromagnetic radiation occures. Am I correct?
Here goes. Imgine changing electric and magnetic fields originating from a fixed location in space. This will ...
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A program to model classical EM field?
As per title, i would like to ask if there exists a program where i can create an arbitrary wire with an arbitrary current and get a visualization of electric and magnetic fields around it.
The ...
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Is there a linear or logarhythmic relationship between scale and electromagnetic force?
Are there any instances where electromagnetic force from a point source doesn't follow the inverse square law?
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MicroTeslas As Gamma Radiation Unit
I live in Poland and currently due to international situation (War in Ukraine) there is quite high risk of nuclear attack here. I also live in capital which makes it most probable target. This is why ...
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How can the electric and magnetic fields be non-zero in the absence of sources?
I'm taking E & M II this semester, and one question got me thinking. We know the formulation of the four Maxwell's equations, and that's okay so far. But in the absence of sources, they take the ...
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What is the exact correspondence between light and an alternating electric field?
When discussing the high-frequency dielectric constant $\epsilon_{\infty}$, it will be said that it is used to describe the response of the dielectric to the applied high-frequency alternating ...
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Balmer proportionality
How did Johannes Balmer arrive at
$$
\lambda \propto \frac{n^2}{n^2-4}, \quad (n=3,4,\dots),
$$
and then how did Rydberg mathematically derive
$$
\frac{1}{\lambda}=R\left(\frac{1}{n^2_1}-\frac{1}{n^...
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How can a plane wave induce perpendicular motion in particles, when the plane wave only carries longitudinal momentum? [closed]
An electromagnetic plane wave moving in the $z$-direction
$E(x,t) = E_x \cos(k z - \omega t), \hspace{1cm} B(x,t) = B_y \sin(kz-\omega t)$
has field momentum in $z$-direction. But according to this ...
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Lunn's Theorem on Solenoidal Fields and the Vector Potential
In 1909 Lunn (section 2) proved the following theorem: "A necessary and sufficient condition that a vector function be solenoidal is that it admit of representation as the vector product of two ...
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Isn't the free space really the radiation zone?
In free space, where there are no charges or current, it follows from $\nabla\cdot\vec{E}=\nabla\cdot\vec{B}=0$ that the electromagnetic waves are transverse i.e. $\vec{k}\cdot\vec{E}=\vec{k}\cdot\vec{...
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Poynting Vector from a Black Body
Suppose I have a cavity with rough walls that is close to an ideal Black Body. For simplicity, assume that it is a square box. I cut a small hole in the box of size $dA.$
Energy would radiate away ...
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How do i interpret the far-field expression?
The 2nd Hertzian dipole antenna of length $l$ is located at $(0, d, 0)$ with current densities:
$$\vec{J_2} = \hat{x} \ I_2l \delta(x)\delta(y)\delta(z).$$
For the $x$-oriented dipole, show that the ...
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Does natural/unpolarized light have a well defined classical electromagnetic field?
The typical model for unpolarized light consists of two linearly polarized waves at right angles to each other, where the phase difference changes randomly every so often. Instead of two linear ...
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Is high school wave peak equation accurate enough for real world?
After preparing for my physics test I came across the equation for calculating peaks and valleys of light in double slit experiment - $N\lambda = dsin\theta$. But, looking at how it is proven. I'm ...
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Seeing trajectory of light
I had gone through a few posts on this topic in this community,however the doubt i have is different from them a bit. There it was said that we do not actually see a laser beam unless they are ...
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How radiative heating of a gas should scale with gas density [closed]
Let's say I have a gas in a fixed volume being heated by a uniform, monochromatic light source.
I'd like to know how the radiative heating rate per unit mass of the gas in J/kg/s scales with the ...
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Guided waves: showing geometrically that $v_p v_g = c^2$
In griffith's introduction to electrodynamics p.430 there's a Figure 9.25 of the wavefronts. I'm wondering if we can show geometrically $v_p v_g = c^2$ using this kind of figure. I think so, but I can'...
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Radiation of an object with a temperature gradient
Case 1: Suppose I have an infinite slab of thickness $D$ connected on one end to a heat bath at temperature $T_B.$ The other end of the slab is exposed to a vacuum, and is at temperature $T_E.$ The ...
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Question on black body radiation
In black body radiation at thermal equilibrium, the absorptivity is equal to emissivity (to conserve energy). Is it fair to say that all of the photons falling on the body are absorbed and emitted? If ...
