# Tagged Questions

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### How can we derive that an accelerated charge particle will radiate EMWs?

All the properties of the electromagnetic entity is said to be fully described by the four golden rules of Electromagnetism : The Maxwell's Equations.How can we derive that a charged particle will ...
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### Electric charge of light? [duplicate]

Light (or any radiation as a matter of fact) is an electromagnetic wave so why doesn't it have a electric charge associated with it? As far as I know only static or flowing electric chargers can ...
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### Can various wavelengths participate in C/D Interference?

My question is can multiple wavelengths or at least two different wavelengths interfere with one another? I know that they usually have to be the 'same' wavelength, but you'd think they can vary a bit ...
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### Why group velocity represents energy or information transmission? What relation between phase velocity and special relativity

I have two question, why group velocity represents energy or information transmission? what is the relation between phase velocity and Special relativity: why can it exceed C without violation of ...
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### What is the meaning of this “let there be light” joke?

A middle school teacher across the restaurant is wearing this shirt, and I certainly don't get it.
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### Why would a rotating charged sphere not have time varying electric field?

I have seen Gauss Law being used for a uniformly charged hollow sphere rotating with $\omega$. How is that valid to use Gauss law since it is an electrostatic law and if it is valid, why do we get a ...
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### The difference between EMR and lone Electric and Magnetic fields

I fail to understand the true difference between EMR and electric and magnetic fields. When current flows, there is an electric field due to the electron flow and a magnetic field, however no EMR ...
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### Sequence of E and B field in radio waves and in single photons

In antenna technology we distinguish between nearfield and widefield. In the nearfield the electric and the magnetic fields are shifted by 90°. If you look closer you can see that there are two ...
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### Poynting Vector Volume Integral Inside a Cavity

Given an electromagnetic wave in resonance mode in a vacuum cavity inside a perfect conductor, on the boundary, the parallel component of $E$ field vanishes, and the perpendicular of component of $B$ ...
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### Acceleration of a unit vector in the Feynman Lectures

In the Feynman Lectures on Physics chapter 28, Feynman explains the radiation equation $$\vec{E}=\frac{-q}{4\pi\epsilon_0 c^2}\, \frac{d^2\hat{e}_{r'}}{dt^2}$$ The unit vector $\hat{e}_{r'}$ is ...
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### What is the relationship between the electric field E and the magnetic field (aka magnetic flux density, magnetic induction) B of a single photon? [duplicate]

I'm looking for a formula for light, for example with 660 nm wavelength, which describes the maximum of the amplitudes for the wavelength of the electric and the magnetic field of the propagating ...
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### In scattering, how does a particle 'know' which direction it is being illuminated from?

In scattering experiments, for example light scattering, the scattering strength from different sized particles is depicted as below. What I can't understand is: how does a particle know which ...
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### How to understand “accelerating charge radiate” using intuition? [duplicate]

While I know that accelerating charges produces EM radiations (at least in lots of cases), most discussion about this matter only focuses on which kind of situation will emit EM radiations and which ...
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### Do radio waves travel around the Earth or through it?

Whenever you hear someone illustrating/describing the transmission of radio waves they always make it seem like they'd travel perfectly around the Earth to another distant location. For example, a ...
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### Curl of an electromagnetic wave?

I can't understand the concept of the curl of an electromagnetic wave. $$\nabla \times E = -\frac{\partial \textbf{B}}{\partial t}$$ All of the examples I find show a current through a conductor, ...
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### Electromagnetic waves and group velocity

I have three questions about electromagnetic waves and was wondering whether anybody here could comment on these things: Wikipedia says that there are no longitudinal EM waves, although TM and TE ...
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### Constructive Interference of Electromagnetic Waves

So I was wondering if Electromagnetic wave has the same property of interference as normal waves. I understand that both the electric and magnetic parts of the wave would have to be in the same ...
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### What does it mean for an electromagnetic structure to be resonant?

There are many electromagnetic structures used in microwave engineering and EM devices. For example, patch antennas, metamaterials made from unit cells, etc. When they design structures like patch ...
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### Visualization of electromagnetic field [duplicate]

In the Wikipedia article about electromagnetic radiation one can find the following picture: But shouldn't the E and B field be 90$^\circ$ out of phase? In the depicted way the energy isn't ...
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### Signal Induction in a Wire due to Alternating Current

I wanted to make sure I understand induction well enough. Assume we have two wires running parallel to each other. Wire A has a signal of $f(t)$, wire B has a signal of $\hat{f}(t)$. Let's connect a ...
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### Can a single photon induce current in a very small coil?

As I know from Lenz's law, I can induce current in a coil just by changing the magnetic field flux inside the coil. As I know from physics course, photons are electromagnetic waves (so they are the ...
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### From power of a laser beam to electric field amplitude

In my experiment, I use a laser beam with wavelength $\lambda=894 \text{nm}$ for some magnetic resonance experiment. Right now, I'm doing some calculation using Quantum Mechanics, which requires the ...
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### What is absorption of an electromagnetic wave?

Can any one explain the absorption/transmission/reflection of electromagnetic waves in the wave form? It is generally said that the atom absorbs/reflects/transmits photon. But can this phenomena be ...
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### Is a Perfect/Lossless Mirror possible?

In traditional mirrors, some of the input light is absorbed by atoms in the mirrors surface and are 'lost' as heat, degrading the quality of the reflected image. Could this loss be compensated by an ...
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So we know that the EMF is induced by change of flux. The thing that was always confusing me is the following: we start changing the magnetic field which in turn induces electric field which makes ...
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### Earnshaw Theorem for ionic solids

Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable? How can I reason this based on Earnshaw's theorem?
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### Optical chirality and its possible hierarchy of generalizations

Optical chirality refers to a constant of motion of the electromagnetic field, which measures in some sense how chiral a light field is. Specifically, the pseudoscalar quantity  ...
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### Is light electromagnetic waves or quantumn particle waves? [duplicate]

Is light electromagnetic waves or quantum physical particle waves. Or are they the same? Note: My question is specifically how electromagnetism plays into the quantum physics and the double slit ...
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I have trouble in determining the "+" and "-" sign of momentum per unit time, per unit area of the following question. Why in the second part, $d\vec{a}$ is pointing in the $-\vec{z}$ direction? I ...
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### Electrons Orbiting Sphere Magnet in Crooke's Tube

Were I to assemble a Crooke's Tube and insert a spherical magnet, with the poles of the magnet perpendicular to the electron stream, would the electrons begin to orbit the poles of the magnet as in ...
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### Would electromagnetic radiation impart a pressure on a surface of neutrons?

In my physics textbook, it says that a qualitative way to envision pressure from EM waves is as follows: the electric field drives charges in the $x$ direction, and the magnetic field then exerts on ...
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### Why doesn't the magnetic field polarize when polarizing light?

If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?
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### How could electromagnetic waves propagate through space although they have no electrons?

How could electric fields in these waves propagate through space although in space there's no electrons for the electric field to be formed? is there another type of charged particles that carry the ...
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### How to compute radiated power from known instantaneous potential distribution

Friend of mine has a device that has an oscillating electric potential and he wants to know how much power it radiates. He can simulate the instantaneous electric potential using a software package, ...
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### Is every electromagnetic radiation considered “light”?

Somebody mentioned on Freenode chatroom for physics that All Electromagnetic Radiation are delivered in form of Photons not just light. Is it true? Does that mean if we get a THF electrical ...
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### Can electromagnetic fields be used to shield electromagnetic radiation?

Can electromagnetic fields be used as shielding for electromagnetic radiation?
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### Prove EM Waves Are Transverse In Nature

Why we say that EM waves are transverse in nature? I have seen some proofs regarding my question but they all calculate flux through imaginary cube. Here is My REAL problem that I can't here imagine ...
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### phase difference between incident plane wave incident on a dipole and radiation fields from dipole

i have an incident plane wave and a dipole, consider that plane wave incident on dipole. at this moment what happen for dipole ? we know that after incident of plane wave on dipole, the radiation have ...
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### Would electron degenerate matter be a good x-ray reflector?

I do not know much about x-ray physics or degenerate matter, but I have the intuitive feeling that the high electron density and what must be some crazy band structures in electron degenerate matter ...
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### Deriving and gaining intuition for the equation for the index of refraction $n = \sqrt{\mu_r\epsilon_r}$

I've come across the equation in the title. It relates the index of refraction of a substance to the square root of the product of the relative permittivity and the relative permeability at whatever ...
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### Far Field Diffraction of EM waves: what does the zero frequency signify?

If you have a system of independently radiating electrons/point-charges, the far field distribution of the EM waves can be approximated by the fraunhoffer diffraction integral, or simply by the ...
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### Waveguides Transmission Mode Determination

How do I know if I have TE, TM, or TEM rectangular conductive waveguide? For instance, I am doing a lab where we want maximum magnetic field in the waveguide, does that mean we want the TE because ...
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### Detailed balance formulation in solar cells?

Hello I wanted to know where does the integral of following picture come from and what are the alternatives in it? How and where can i find information i need to know to understand this text? thank ...
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### Difference between Cotton Mouton effect and inverse Cotton Mouton effect

The Cotton mouton effect is observed when a linearly polarized electromagnetic wave passes through a dielectric medium and a magnetic field is applied perpendicular to the direction of propagation of ...
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### Characteristic quantities in Fiber optics

I'm having trouble finding typical quantities in fiber optic communication. In particular, what kind of powers are generally used (or what is the minimum that fiber optics receivers can detect ...
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### How does a MRI use 20.1kW yet creates over 204K BTU/h? [closed]

I've been reading through a manual about MRI operating procedures for a large healthcare provider. The manual (written by Siemens) states that the MRI machines use 9kW in stand-by mode and 20.1kW ...
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### Dynamic light scattering of rods at low q

In dynamic light scattering (DLS), I understand that for spherical particles it is their diffusive motions which cause the intensity fluctuations that are correlated. And that the scattering vector ...
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### Physical meaning of Maxwell's equations and origin of EM waves

Is it possible to describe the physical meaning of Maxwell's equations and show how they lead to electromagnetic wave, with little involvement of mathematics ?