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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Photon distribution from a classical radiative event

I became curious about the number and frequency distribution of photons emitted from a simple radiative event: Small charged object given a mechanical hit. Non-relativistic, not a delta function, ...
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Understanding the $\vec{k}$ and $\vec{n}$ for an EM wave

I am trying to understand the idea of the EM-waves and the meaning of the $k$ and $n$ vectors and how can I read them from the given E-field. Let us suppowe we have a E-field in the form of $$\vec{E} =...
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Do surface charges exist when EM wave gets reflected by dielectric boundary?

If both the materials on a boundary are dielectric then do surface charge exists. While soving for reflection coeffecient it wass sufficient to satisfy tangential componenta, I was solving using ...
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Instantaneous ejection of photoelectrons indicative of particle nature of light?

My physics textbook under a section explaining about How wave nature of light does not explain Photoelectric effect, mentions the following: No matter how small is the intensity, photoelectrons are ...
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Introduction to electromagnetic waves with easy math

My father would like to understand the physics of light (let's say Maxwell's theory, the wave-particle duality and special relativity) and he's asked me what book he should read. He's a quick learner, ...
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49 views

Electromagnetics - how to choose a proper normal vector? [closed]

In D.K.Cheng's equation 8-29 he makes the following correlation between the magnetic field intensity $\mathbf{H}$ and the electric field intensity $\mathbf{E}$ in an electromagnetic wave. Where $\eta$...
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Why is intensity of an electromagnetic wave independent of its frequency?

In electromagnetic theory, we define electromagnetic waves as two fluctuating electric and magnetic field which travel in a direction. We have a property called Poynting vector which is the power per ...
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5answers
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What is the physical meaning of frequency in the wave concept?

Treating light as a wave, we define its frequency. We see that light with different frequency have different colour. But, why? In wave, what property or physical meaning does frequency provide?
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Are the components in an electromagnetic wave each others' mediums?

Is it right to say that the electric field serves as a medium for the magnetic field to propagate and the magnetic field serves as a medium for the electric field to propagate in an electromagnetic ...
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How to choose the surface for the magnetic flux in case of an open circuit (Faraday Law)?

I have a doubt about a topic about which I did not found many informations. Each time I've applied Faraday Law ($EMF = -\frac{d\phi(B)}{dt}$), such magnetic field crossed a loop conductor (for ...
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What will happen to the crayon coloured paper when we supply white light continuosly?

a) I do understand that visible light is also part of electro magnetic spectrum and will have a wavelength , amplitude and frequency. b) This photons will be generated when electron moved from higher ...
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What kind of waves are photons? [duplicate]

whenever I heard of the "wave-particle" duality of photons, I always thought they existed as a weird combination of physical waves and particles. Since finding about De Broglie wavelengths ...
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Are very massive neutron stars highly streching wavelenghts of their emitted light?

Can be possible that more massive or more denser neutron stars stretch the wavelengths of their emitted EM-waves more than less massive and less denser neutron stars?
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If all objects emit IR radiation, would it be sufficient to place an IR mirror behind an object to propel it forward?

I'm assuming objects don't move all the time because they emit IR radiation in all directions. If we have an IR mirror behind the object to focus their direction, would this propel the object forward?
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The wave nature of light

Light is an electromagnetic wave composed of electric and magnetic components. I recently read that the velocity of light is in the direction $\mathbf{E}\times\mathbf{B}$ where $\mathbf{E}$ and $\...
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Hypothetical black light

Was the eye to be hit by a very intense source of pure UV radiation (in the hypothesis of absolute lack of any other stimuli), which color would the brain elaborate from said stimulation? Basic black? ...
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Making sense of cavity in a 3 ropes system

I fail to understand why cavity resonance happens. Let's say for the sake of example we have 3 ropes, the first and the last half-infinite and the middle one is of some length $L$. Now, we generally ...
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Electromagnetic plane wave Mathematica representation [closed]

I've been searching for a working way to represent an Electromagnetic plane wave with Mathematica and with the arrowheads like in the following picture, but I haven't been able to achieve my goal. If ...
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Exactly what is the cause for the zero reactance seen in the impedance at the center feed point of a resonant half wave dipole?

Lots of explanations i've read on the internet written by ham radio operators and in some text books state that a half wave dipole is resonant when the inductive and capacitive reactances cancel out. ...
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Why Gaussian Beams are Eigensolution?

On the book principle of lasers by O. Svelto, it is written that Gaussian beams are eigensolutions of the paraxial wave equation (written in integral form). I don't understand why these beams should ...
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2answers
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What are matter waves made of and what is their speed?

We know electromagnetic waves are made of oscillating electric and magnetic fields that can travel at the speed of light without a need for a medium. But, how about matter waves proposed by de ...
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1answer
34 views

Spacetime as a medium for electromagnetic waves? [closed]

We typically break waves into two separate types mechanical waves and electromagnetic waves and treat them entirely differently based primarily on the observation that electromagnetic waves don't ...
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Is there one photon per wavelength of light? [duplicate]

This makes intuitive sense to me but I have never heard anyone confirm it. Is it one photon per wave length or does it approximate one wavelength or something else?
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Transition between vibronic states and the meaning of transition dipole moment

Let's say we have a molecule which belongs to $D_{3h}$ point group. The IRREPs of inital and final states are as follows $A'_{1}$, $E'$. Hence, the IRREP for the dipole moment has to be $E'$ so that ...
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Isn't the direction of propagation wrong in this diagram from wikimedia commons?

The direction of propagation of an electromagnetic wave is given by the Poynting Vector \begin{equation} \boldsymbol{S} = \frac{1}{\mu_0} \boldsymbol{E} \times \boldsymbol{B}. \end{equation} This ...
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Big problem with the standard derivation of Rayleigh-Jeans law + reason for this standard approach + solution

The problem: The standard derivation of the Rayleigh-Jeans law, in a cubic reflective cavity with a small blackbody in it, would have you believe that the cavity has an energy density of $kT$ for ...
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38 views

Which expression represents a plane wave propagating in free space? [closed]

Using the usual notation for rectangular (Cartesian), cylindrical, and spherical coordinates, which of the following expressions represent a plane wave propagating in free space? $$e^{-jk_0R\sin(\...
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Intensity of light passing through polarising filters

I came across a question in my Textbook which I am unsure about. Two polarising filters are aligned to transmit vertically polarised light. They are held in front of a source of horizontally ...
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34 views

How do Fluorescent molecules emit light in a different wavelength than the one needed to excite them?

if it took a very certain amount of energy to excite an atom, how come when it de-excites it emits a photon of lower energy? I know that's what scintillators do, I Just want to know the microscopic ...
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How to apply Maxwell's equations to electromagnetic waves? [closed]

You know how antennas work and create EM waves...They oscillate charges which create EM waves Well I'm not satisfied with that explanation so it would be great if you could use maxwells equation to ...
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1answer
23 views

EM Wave Reflection and Transmission Between with Anti-Reflective Coating

I am trying to solve a problem in which light is normally incident on a material of refractive index n which is coated with an anti-reflective coating of refractive index $n^{\frac 1 2}$ and thickness ...
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2answers
81 views

Why do electromagnetic waves detach from the antenna?

In most explanations of how antennas work they say that because of kinks in the electric field of an antenna meets at one point and detaches... I looked up reasons for why this happens but all I got ...
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Vibration of particles in EM waves

We can find the direction of vibration of a particle by shifting the wave in the dirction of wave travels. Is this applicable for EM waves as well?
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Does an antenna emit EM radiation in all directions?

You know how an antenna works? It creates EM fields and oscilates them so that it creates electromagnetic fields...Well does that electromagnetic wave travel in a straight line or spread out ...
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Do metal objects improve radio signal reception when standing nearby?

I have a watch (Casio G-Shock GW-M5610 ) which can synchronize itself to radio time signals. In my area it uses DCF77 tower, which transmits 77.5 kHz (approximately 3868.3 m wavelength) signal: The ...
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91 views

Wavefronts, refraction, and the marching soldiers analogy

I am not a physicist, but rather a middle school science teacher. Please be gentle. The marching soldiers has been a really good analogy for explaining why a change of direction is caused by hitting ...
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Why isn't the direction of magnetic field all around the electric field( in circles) in an electromagnetic wave?

Why isn't the direction of magnetic field all around the electric field( in circles) in an electromagnetic wave? (Instead it is shown only in a single direction in the diagrams)
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Can you convert light to radio waves

Can light be converted to radio waves by reducing the frequency of electromagnetic waves? If so how do you do it? And how much energy, approximately in percentage, would be lost during the conversion?
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Why does a shorter-wavelength laser beam diverge less than a longer-wavelength one?

Also, does this phenomenon apply only to lasers, or also to other EM beams? I wonder if the answer is related to the fact that diffraction limit(s) are proportional to wavelengths...
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What do photons look like?

We have many theories that advocate the particle nature of light. But have we ever observed photons physically? If so: what do they look like? How big are they? If not: why not? Is it because they ...
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Signal reflections on conductors at low frequencies where they are not transmission lines

This question might be suited for the Electrical Engineering forum, but I think I might get more scientific explanation/discussion (rather than anecdotal) on this forum. Is the reflection phenomenon ...
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2answers
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Do we take into account the physical angle between Electric fields and Magnetic fields during interference of light?

I have been studying interference of light waves for a while now and I have a doubt. I have never seen any sources (books, internet , teachers) ever take into consideration about the "actual"...
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275 views

Why is this electromagnetic field a wave?

In D.K.Cheng's Field and wave electromagnetics he states the following: The phasor electric field intensity for a uniform plane wave propagating in the +$z$-direction is $$\mathbf{E}(z)=E_0e^{-jkz} $$...
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350 views

What is the physical meaning when we say complex waveform has an energy at certain frequency?

We say that a complex periodic wave has an energy at certain frequencies. Or we can also say that such waveform has a certain “frequency component”. I understand that mathematically it means we can ...
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Discrete Cavity Radiation vs Continuous Blackbody radiation, violation of the 2nd law of thermodynamics?

Blackbodies emit a continuous spectrum of radiation, whereas a cavity with reflective walls at thermal equilibrium contains a discrete spectrum. According to Kirchoff, "smoothing out" the ...
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Why is Light an EM wave?

Well, the definition of electromagnetic waves in a couple of textbooks is stated to be, 'A wave produced or resulting from the accelerated motion of a charged particle'. My question is straightforward-...
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3answers
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How could I see the distance light traveled from an airplane?

It was nighttime. I was flying on an airplane. As we were landing we passed over a highway. I saw cars below with their headlights on. I could see that the light from their headlights only lit up a ...
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Experience to see if an accelerated observer detects radiation

I will consider $\textbf{spacetime}$ as $(M,\eta)$ where $M$ is a four dimensional $\textbf{manifold}$ and $\eta$ the metric which in this coordinates $$ \begin{align*} x \colon M &\...
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Determine the direction of electric and magnetic field in for plane EM wave

A problem states that Measurement of the electric field (E) and the magnetic field (B) in a plane-polarized electromagnetic wave in vacuum led to the following: $$ \begin{array}{ll} \frac{\partial E}{...
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How fine can single photon detectors made to be?

It is said that light behaves like a wave until it is measured, then it behaves like a particle. Photons (the particles) then have to be defined by the measuring device. It is my understanding that ...

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