Questions tagged [electromagnetism]
The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
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UV absorption mechanism of the wooly hairs of the alpine edelweiss
I've read a paper about this photonic structure with corrugation arranged with gaps of similar wavelength to UV light. but the mechanism of how they interact is unclear to me. I still don't understand ...
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Missing term in multipole moments for long wavelength limit - Jackson Chapter 16
In Jackson's Classical Electrodynamics (1st edition), Jackson writes an expression for the electric multipole moments in the long wavelength limit in equation (16.93), (16.94):
$$a_E(l, m) = \frac{4\...
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Energy Conservation in Capacitor with Inserted Metal Plates [closed]
We insert two metal plates pressed together inside a capacitor:
Capacitor Plate 1 -> MetalPlate1+2 -> Capacitor Plate 2
After reaching equilibrium, we separate the two metal plates between the ...
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What I think about surface charges in electrical circuits
Assume We have a simple electrical circuit with a DC Source of constant emf.
And I am talking about the ideal case.
The circuit also consists of "Push-Key" or a normal switch whatever you ...
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Upper and lower bounds in integral for potential
So I have problem with understanding and determining electric potential. I'm going to explain how I think through an example and where it the breaks down in another example.
Example 1 from griffiths ...
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Why can't we directly relate the magnetic field $ \bf B$ to the electric field $\bf{E}$ using the equation $∇×\bf{B}= μ_0σ \bf{E}$?
Why can't we directly relate the magnetic field ${\bf B}$ to the electric field ${\bf E}$ using the equation $\nabla \times {\bf B} =\mu_0 \sigma {\bf E}$?
In my understanding, a steady electric ...
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Does the “wave” solution contain every solution to the Maxwell’s equations?
I was thinking that we obviously do have wave solutions to the Maxwell equations. We might have some other solutions, such as $E = 0$ and $B = 0$, which are the same as the wave solutions with the ...
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Does an atom absorb a twisted light photon and emit a twisted photon? [closed]
Does an atom absorb a twisted light photon and emit a twisted photon?
How can it emit a twisted photon?
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How exactly to prove Thomas precession from Jacson first ed
How exactly prove (11.50) and (11.52) from Lorentz transform ?
$ t'' = t' - \frac{\mathbf{x'}}{c^2} \gamma (\delta \mathbf{v} + (\gamma - 1) \frac{\mathbf{v}\mathbf{\delta v}}{v^2}\mathbf{v})$
$ \...
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Confused about selection rules in optical transitions
This question is motivated by this paper in particular (let me know if it is not open access). They measure transitions between electronic levels inside an ion, placed inside a crystal. In Fig. 2, ...
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Are the accelerated charges the real reason for the magnetic induction? [closed]
I have watched an explanatory video from YouTube that stated that the real reason for the "magnetic induction" are electric field lines of an accelerated charge, that have a component in the ...
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Why is using an RF magnetic field equal to the Larmor frequency best for NMR?
I'm working on a lab on NMR and am trying to get a good picture of what is going on.
From what I understand: We take a piece of material and place it in a strong magnetic field $\vec{B_0}$. The ...
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Back-EMF in a DC motor as a Sine Wave?
I am taking time to re-familiarize myself with the design and principles behind the operation of dc motors. I am right now trying to understand back-emf. Forgive me if I seem to have a piecemeal ...
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Finding Instantaneous value of alternating sources using phasors
Phasors are the vectors which would rotate about origin in anticlockwise direction. They are generally used to study about phase angles of varying quantities like alternating current, voltage,etc. In ...
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Motional EMF in a Square Loop [closed]
Consider a square loop of side 2 metres moving along positive X-axis with a velocity of $2 \hspace{0.07cm}ms^{-1}$ in a uniform magnetic field of $2 T$. The question is to find induced emf. But there ...
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Why does the tension change instead of the speed of this object undergoing circular motion?
I recently came across the following problem:
A charged particle is whirled in a horizontal circle on a frictionless table, by attaching it to a string fixed at one end. If a magnetic field is ...
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Magnetic monopoles in materials
What types of materials would conduct magnetic monopoles well? Would it be materials with a high 'mu' as with regular magnetic fields? Thank you.
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What is the electric field inside an inductor?
In a simple LC oscillation a charged particle was kept in the centre of solenoid ie inductor. At t = 0 will it experience any force? According to me since the particle is in center it won't ...
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Why the Electrical field is that way? [duplicate]
So, I asked my teacher to draw the incident and reflected wave in the case of the incidence onto a perfect electric conductor. The thing I Don’t undersand is why the reflected field is that way. The ...
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How can we derive the polarization of reflected electric field? [closed]
Simply out: How can we derive the polarization of a reflected electric fields in the case of parallel polarization, where the electrical field lays on the incidence plane
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Griffiths image methode surface charge density
As Griffiths says:
there is a charge $q$ at a perpendicular distance $z=d$ from an infinite conducting plate $z=0$. We use the image method and place $−q$ on the other side of the plate and calculate ...
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Current solver (code) of surface of PEC, for example dipole, Antenna Problem [closed]
I already did the hallen integral equation method and it is not precise enough, therefore I was trying to apply a more general method using the EIFE, and a more realistic modelled source.
Therefore I ...
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Derivation of the Classical Lifetime of Hydrogen
In derivations of the classical lifetime of a hydrogen atom, the key assumption seems to be that the orbit is circular, allowing us to write
\begin{equation*}
\frac{mv^{2}}{r} = \frac{q^{2}}{4\pi \...
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Ampere-Maxwell Law for Resistor in AC circuit
Let's say we have a resistor ($R$) attached to a sinusoidal voltage source ($V = V_0 \sin{\omega t}$) so that we get a changing sinusoidal electric field inside the resistor. We construct an Amperian ...
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Physical reasons for representing Maxwell equations using TWISTED (exterior) differential forms [closed]
What are the physical reasons for representing D,H,P,M,J as twisted (odd) differential forms and E,B as untwisted (even) differential forms? Most materials I've read, even those focused on ...
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Vector Potential and Electric Field
In Yu's Fundamental of Semiconductors, they derive the amplitude of the photon's vector potential (6.32, page 258) when discussing the electron-radiation interactions to be
$$
A=-\frac{E}{2 q}\{\exp [\...
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Physical interpretation of Lorentz and Fano resonance
I'm currently studying about lorentz oscillation and fano resonance (ref: https://doi.org/10.1088%2F0031-8949%2F74%2F2%2F020).
According to the lorentz model, also known as driven damped oscillated ...
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Transformers, AC and DC current
I have a question about transformers and how do they work: I know that the main principles behind a transformer are the mutual induction and Faraday's law; in order to have an emf induced in the ...
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Formal description of an electron absorbing a photon
This question is about how the electromagnetic field interacts with matter.
Suppose we have an electromagnetic wave, let us say it is planar but not monochromatic. So the wave is described by an $L^1$ ...
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How does an electromagnetic wave warp spacetime?
I am trying to understand how an electromagnetic wave would curve spacetime and what effect this curvature in turn would have on the wave.
I am imagining an electromagnetic plane wave travelling in ...
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Induced emf and coil winding direction
Recently, I've learned that induced emf is there to oppose the change in magnetic flux.
consider a current increasing over time ($\frac{di}{dt}>0)$, moving left to right as it passes through the ...
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Does the magnetic field you find depend upon the size of the Amperian loop?
Will the value of magnetic field change if my amperian loops are changed if I am calculating it for the same current?
For example, if I take an infinitely long straight conductor, does magnetic field ...
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Do electromagnetic waves really slow down? [duplicate]
I have read somewhere that electromagnetic waves, when refracting only "appear" to slow down. That is when the wave goes thorough a material like glass it vibrates the electrons in the glass ...
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Direct derivation of retarded fields in electrodynamics
Rather than first selecting a specific gauge, writing a guessed solution for the potentials within that gauge, and then differentiating them to obtain the fields, can we instead directly derive the ...
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How many times do you need to drop a magnet for it to lose it's power? [closed]
How many times do you need to drop a magnet to the ground for it to lose it's power ?
Is there a way this is measured ?
Thanks!
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Changing the magnetic field of earth
I am familiar with the concept of toroid which causes an electromagnetic field.
Is it possible, if we make a large enough toroid, to change the magnetic field of earth.
If yes, then how will it affect ...
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Quantised electromagnetic field in quantum optics for an infinite quantiation volume
The electromagnetic field can be quantised by considering the allowed modes in a cube based on the periodic boundary conditions and then quantising those modes. Doing so, we find that the hamiltonian ...
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Faraday tensor index calculation
I have seen the following equality in a book about analytical electrodynamics:
$$\mathbf{\frac{\delta F^{\mu\nu}}{\delta A_{\rho}}F_{\mu\nu}+F^{\mu\nu}\frac{\delta F_{\mu\nu}}{\delta A_{\rho}}=2F^{\mu\...
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Formula for $TE(M,0,N)$ mode of microwave cavity
I am interested in the general formula for the magnetic and electric field of a TE mode of a 3D microwave cavity.
In Pozar's Microwave Engineering Book, the formulas for the fields of a 3D cavity with ...
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Eigenvectors of the Cold Plasma Dispersion Relationship
I'm currently making my way through the textbook "Introduction to Plasma Physics" by Donald Gurnett. In section 4.4.2: Propagation Perpendicular to the Magnetic Field, the equation for ...
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Why do passive materials impact magnetic field? [duplicate]
When calibrating magnetometers you need to consider the soft-iron distortions, from my understanding they are basically passive materials that deform the magnetic field.
I'm curious why these passive ...
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Dielectric constant and Refractive index with drasticly different behavior for biological tissues
Here's the context, similar to my last question but a bit different. I'm studying stacked biological tissues assumed to behave like dielectrics. Using the modified cole-cole equation:
$$\tilde{\...
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Question about electric flux in curved spacetime
I just started physics II (electricity and magnetism) and in learning about Gauss's Law, I came across this definition on Wikipedia:
$$\Phi_E=c\oint_{S}F^{\kappa0}\sqrt{-g}\ dS_{\kappa}$$
Where $c$ is ...
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How to show the ratio (spin angular momentum density)/(energy density) for circularly-polarized gravitational plane wave = $\pm 2/\omega$?
It is well understood that an infinite monochromatic, circularly-polarized electromagnetic plane wave has no angular momentum density. However, a finite monochromatic, circularly-polarized ...
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How much electromagnetic force is keeping a chair together? [closed]
I’m not a physicist, so excuse my poor wording.
In an average chair, roughly how much attractive force from the electromagnetic field is keeping it together?
If you want to go further, how much force ...
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Solve for the shape and curvature of Earth's magnetic field
How can I solve for the shape of Earth's magnetic field (neglecting the effects of the solar wind which distort it). It looks very similar to the field due to a solenoid, but I can only find solutions ...
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Units of the action of a charged particle in four-potential coupling
I have a question about the definition of the action that Landau defines as:
\begin{equation}
S= -\frac{e}{c}\int A^{\mu}dx_{\mu}
\end{equation}
he says that the $1/c$ factor is introduced by ...
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Why doesn't an EMF source directly affect the internal charges in a wire, but only the surface charges
So for current to flow, an EMF source such as a battery causes surface charges to form a gradient along the wire. These then have local fields which cause current flow by moving internal free charges.
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Field profiles using Transfer Matrix Method [migrated]
I am using the Transfer Matrix Method to compute optical properties such as reflectivity, transmittance as well as to obtain guided modes for multilayer structures. Following the formalist presented ...
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Why in IE Irodov the formula for energy of a system of electrical charges an additional factor of 1/2 is mentioned?
I think that it instead be something like W=sigma(qiVi)
