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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Two molecules with different polarizability in a EM field

If I have two molecules with different constants polarizabilities $\alpha_1$ and $\alpha_2$ and I send and EM field first on the molecule no.$1$ and then on the molecule no.$2$ so that the two ...
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Can Two Electromagnetic waves cancel each other if it 180 degree phase moving in same direction?

If we can send two electromagnetic waves -180 degree out of phase- in same direction, then the interaction of this wave with air molecules will be less due to the low intensity of the combination. So,...
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Radio Frequency Identification System (RFID) Analogue versions for warehouse [closed]

Are there any analogues of RFID tracking system? How do you think, for example what can be used in cloth shops instead of RFID? Any answer is welcome, i just need some imagination
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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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Can Rutherford model (1911) be "saved" if the orbiting electron in the atom is divided into sub-particles? [closed]

The well-known contradiction of the Rutherford atom model (1911, a planetary atom model) is that the electrons rotating around the nucleus will be emitting the electromagnetic waves, thus losing ...
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What's making the scenario contradictory to Maxwell's theory of em waves?

I was imagining how an oscillating charge would produce an electromagnetic wave and I got stuck at a point. We know that the direction of propagation of em waves is perpendicular to both the ...
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Absorption spectrum of white light of the Sun

When some photons in the white light from the sun are absorbed, this means some wavelengths will be missing, so how does that light still appear 'white', although some of its constituents are missing?
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An antenna can send electromagnetic wave which brings the energy flow to the outside of our universe, is this true? [closed]

According classical electromagnetic field theory or Maxwell's equations. The Poynting vector of the electromagnetic wave of an antenna is real and point to the outside of our universe. Our universe is ...
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How to make light resonance? Is this a proof that c is not constant in lasers? [closed]

How to make light resonance? I know that it's possible to amplify electromagnetic waves e.g. $$LCR \ \ \ \ f_0 =\frac{1}{2 \pi \sqrt{LC}}$$ but how about light resonance? $$A*f=\frac{c}{2\pi} $$ Btw ...
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Why do Greenhouse Gases absorb heavily in certain wavelengths?

What molecular properties make greenhouse gases absorb and reemit primarily IR radiation? That is, why are CO2, H2O and NO2 all greenhouse gases (GHGs), but others (such as helium and neon) aren't? ...
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How exactly is electromagnetic radiation the way it is?

Electromagnetic radiation from sun is more likely produced by the nuclear fusion, and at a go radiation is released but how is it possible for different types of radiation to be produced such as, ...
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Does the absorption of ionizing radiation increase the absorber temperature?

Let's say a gamma ray shielding material (assume water) has absorbed 1 joule of gamma ray ionizing radiation, does the absorbed 1 joule eventually end up as heat in this material? I ask this question ...
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How do I calculate the induced voltage on a finite antenna

I'm trying to calculate (numerically) the induced voltage on a half-wave dipole caused by a moving charge as a function of time. Up to this point the way I have been doing this is using the formula $V ...
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This setup works for polarization. Does it work for wavelength?

In the school I was impressed with the following experiment: there are two polarization filters with orthogonal polarization directions placed at a distance from each other. They do not allow any ...
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What formalism is used to model thin film optical coatings that function across a range of angles of incident light?

Thin film optical coatings [0] are atomically/molecularly thin layers of material applied to a substrate with the intent of affecting the optical properties of the substrate. For example, magnesium ...
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Why is the refractive index $n$ linked to the wavevector $\hat{n}$?

Preamble: I'm studying light-light scattering in Effective QED but I notice that I don't remember a single thing from my EM/Optics courses so I decided to review some things. Question: why is the ...
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Does an accelerating neutron produce electromagnetic waves?

I believe both protons and electrons do produce e/m radiation if accelerated, but what about a neutron which is made up of, or at least decays to, an electron and a proton? If accelerating a neutron ...
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Why does EM wave propagate perpendicular to cavity wall in Rayleigh-Jeans Law derivation

I’m trying to follow the derivation of the Rayleigh-Jeans law in my textbook by Eisberg and Resnick. A cubic cavity is considered and the following is said of wave’s orientation relative to the wall: ...
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What does light travel through or why it is independent of a medium? [duplicate]

According to my research and understanding I cant get over the fact that light needs no media to travel, or is it scientifically or mathematically proven?
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How does a photon interact with a conduction band electron?

In conductors the valance and conduction band overlap so there are free electrons. If a radio frequency photon hits one of those electrons (as in the case of an antenna), what will that electron do? ...
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Relativistic momentum of the E.M field vs Poynting momentum questions

I come somehow to the following thoughts: The energy of the EM field is $$\mathcal{E} = {\epsilon_0\over 2} (E^2 + c^2 B^2).$$ Associate to $\mathcal E$ the relativistic mass $$m_r = {\mathcal{E}\over ...
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Generalization of Griffith's calculation of the power radiated by a point charge when $\vec\beta(t_r)\neq 0$

In Griffiths's book, Introduction to Electrodynamics, Third Edition, Section 11.2, the author calculates the power radiated by a point charge $q$ in arbitrary motion. The calculation requires the ...
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Why is the electromagnetic wave equation derived from Maxwell's equations with no charges?

After having consulted numerous physics books, forums and videos, in all cases I found that the electromagnetic wave equation is derived from taking as a premise that the medium is a vacuum. This ...
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Is there a filter which can convert light from the sun to Microwaves directly?

Is there a way to filter light from the sun (visible, UV, and/or IR) and convert the energy from it directly into Microwaves without putting in any energy? Barring this is there a way to do the same ...
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How are field gradient lengths understood?

When dealing with waves we can use wavelength as a given parameter. But, how is "length" related when not dealing with waves but rather field's of regularly spaced lines of force ? Dan M.
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Light absorption

When the sun 'sends' light to earth it is a spectrum larger than visible light. Does black paint absorb ALL of the sun's spectrum? including radio waves and gamma rays? If not, then what things absorb ...
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If the EM field is a self-propagating field that doesn't need a media why should space expansion make any changes to its wavelength?

If the EM field is a self-propagating field that doesn't need a media why should space expansion make any changes to its wavelength? If it makes changes to the photons wavelength should it be ...
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How ample is a wave amplitude?

Is it possible to actually measure/deduce the amplitude of a wave? We know that the length of am infrared wave is a fraction of a millimetre, do you have any idea what is the range of the physical ...
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Radio Waves and the Lorentz Force?

Is the Lorentz Force involved when the EM wave intersects the receiving antenna? I.e. induces EMF on electrons in the antenna conductor? I use the RHR with index finger $\vec v$ pointing in the ...
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Why can the hole of a cavity-hole model be considered a radiating blackbody?

It is easy to understand why the small hole of the cavity-hole model simulates an absorbing blackbody as almost all incoming radiation into the hole is captured. Why can we consider the hole an ...
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UV & IR radiation are mostly absorbed by water. Our eyes are predominantly water. If our eyes were made of another liquid, could we see slight UV/IR?

Firstly, I'm not a physics guy. I just think it's neat, that's all. I was reading a post on here about why water is transparent (I was more interested in why milk isn't) and saw a graph that showed ...
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How to calculate the field distribution due to a current radiating in one direction?

Given a surface current distribution, $\textbf{J}(r)$, we can calculate the magnetic potential in the Lorenz gauge using $$ \textbf{A}(\textbf{r})=-μ_{0} ∬g(\textbf{r},\textbf{r}')\textbf{J}(\textbf{r}...
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Apparent instantaneous EM propagation paradox in two concentric solenoids [duplicate]

Assume there are two solenoids $S_1$ and $S_2$ sharing the same axis, one of radius $R_1$ and the other of radius $R_2 > R_1$ resp. For the sake of simplicity, I will assume that $S_2$ reduces to a ...
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Confusion in the showing EM wave exist from Maxwell equation

When deriving the mathematical description of a field, we set the current density and charge to zero in Maxwell's equations. However, this condition is not absolutely true anywhere on earth. Yet, we ...
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How does a conductive medium affect an electromagnetic wave passing through it?

I have a big physics project. I want to investigate the skin effect, and how submarines effectively communicate. I have an experiment idea in mind. I can use an radio wave emitter to emit a radio ...
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Does the quantisation of energy apply to everything? [duplicate]

Radiation is quantised according to Planck, so that's out of the question. However, I have seen many simplifications that claim Planck introduced quantised energy. Period. Has Planck really done that? ...
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Wave Equation in 2D and 3D

I am new to wave mechanics in 2 and 3 dimensions and would like to know: Do you simply add $\partial \psi \over\partial y$ and/or $\partial \psi \over\partial z$ term without the other parts of the ...
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How to reduce magnetic field between two magnetic shield sheets (silicon steel sheets)?

I put 2 parallel silicon steel sheets between magnetic field as below: As silicon steel has much bigger permeability than air,magnetic line will go through 2 silicon steel sheets. What I can do to ...
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How do you make light?

We make light making a charge oscillate, or heating a body. Are there differences between the two processes? But, above all, are there other ways in which we can produce em radiation?
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Show that the energy of the electromagnetic field is given by half the norm of the Fourier transform of the electric field

Following Peskin and Schroeder on page 179-180, I am trying to show that $$\frac 12\int d^3x \left(|\mathbf E(x)|^2+|\mathbf B(x)|^2\right) = \int \frac{d^3 k}{(2\pi)^3}|\mathbf k|^2\sum_{\lambda = 1,...
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Radio Wavefront and Photons?

I have some questions related to radio waves, photons and propagation , transmission and reception. It’s my understanding a radio wave is a changing electrical and magnetic field that travels through ...
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Cavity and black body radiation

If one speaks of the fact that one gets blackbody radiation in good approximation by a cavity with hole, does one mean as blackbody this hole, i.e. the place where the radiation exits from the cavity? ...
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How can light penetrate gold in an astronaut's visor?

Astronaut visors use a thin gold layer to decrease intensity of IR radiation coming from the sun. The thing is, gold is a conductive surface, so how can it transmit light through it. Is this related ...
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Where/ how does light propagate? [duplicate]

The Michelson–Morley experiment proved there is no aether, but we (used to) know that a wave needs a medium in order to propagate. Einstein showed the invariance of speed but assigned no properties to ...
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Failure of Newton's corpuscular theory and success of photon theory of light

Corpuscular theory of light States that: Light is made up of small discrete particles called "corpuscles" (little particles) which travel in a straight line with a finite velocity. ...
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Is there any end to the electromagnetic spectrum? [duplicate]

Is there any theoretical end to the electromagnetic spectrum…
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Non-parallel light diffraction

Does light (and in general any kind of wave) diffract only when the wave fronts are parallel? Like if you did the double slit experiment when the waves were coming from a point source close to the ...
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How does parity work for the electric field and electric dipole and electric quadrapole transitions?

It is known that the electric field is a (polar) vector and is odd under parity. Likewise, when an atom undergoes a dipole transition its parity must flip because the dipole electric field acts like ...
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Degeneracy of Photons

The density of states for a photon gas is defined by, $$D(\epsilon)=\frac{g}{2\pi^2}\frac{\epsilon^2}{(\hbar c)^2} $$ where g is the number of independent internal states for a photon. The question is ...
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What is the wavelength of light in a practical sense?

Okay, so I know that a wavelength is a distance of crest and a trough added together which makes a whole wave, but what is it in the real sense? Like in the case of sound I know when we say "...
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