Questions tagged [electromagnetism]

The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

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17 views

How is magnetic energy supplied?

Enthusiastic layperson here, curious about magnetism: Scenario 1: Imagine that I lift a piece of iron with my arm from a tabletop a fixed distance upwards, then place it back on the table. In ...
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21 views

Chemistry without electrons?

This question on the behavior of a universe with massless electrons got me wondering: what would atoms look like if electrons were not merely massless, but rather the lepton fields just didn't exist ...
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How is Electromagnetic segmented-capacitor propulsion system even possible?

The alledged invention - patent US10006446B2 - suggest to allow creation of lifting force (4) on electrically charged rotating plate when magnetic flux is turned on and dirrected towards the center of ...
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12 views

Difference between Capacitor and a battery [duplicate]

Capacitor stores electric charge and battery also stores electric charge. SO whats the difference between them?
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Removing “electric dipole moment” from non-relativistic Dirac equation

I have found many sources (c.f. Schwartz's QFT book section 10.4) that try to obtain the non-relativistic limit of the Dirac equation by first "squaring it" so that it looks somewhat like the Klein-...
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Potential drop across inductors in DC circuits

The potential drop across an inductor is equal to $L(di/dt)$ where $L$ is inductance coefficient. But according to this in a DC circuit there should be no potential drop across the inductor (because $...
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MCS Lagrangian and Euler-Lagrange

I'm trying to solve the Euler-Lagrange equation for the MCS Lagrangian density as given by Kharzeev in this article (Eqn. 7): $$ \mathcal{L}_{\textrm{MCS}} = -\frac{1}{4}F^{\mu\nu}F_{\mu\nu}-A_\mu J^{...
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63 views

Maxwell equations in curved spacetime with cosmological constant

I am aware of Maxwell Equations in Curved Spacetime. But how do these equations change if the cosmological constant is not assumed to vanish?
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First year university physics book [duplicate]

I am a newbie to Physics stackexchange. I am a CompSci undergraduate, now pursuing an open university bachelors (BS) in mathematics. I am taking a course on vector calculus. To gain a gut, intuitive ...
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Permitivity Constant of Ionized Gas

If I have let’s say an ionized gas, composed purely of singly charged positive ions; what would be the permitivity of the material? Is it infinite, as is the case with a perfect conductor, or am I ...
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Criteria for electrostatic approximation in microscopic/kinetic plasmas

I started pondering about the electrostatic approximation in relation to plasmas, where a particle's motion $\mathbf x(t)$ is governed by the Lorentz force: $$ m\ddot{\mathbf x}=q(\mathbf E+\dot{\...
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How to incorporate refractive index in transfer matrix method

I need to determine the TE and TM reflections at the interface between a uniaxial crystal and air, using a matrix-based method, such as the TMM. I can do so using the Fresnel equation with ease, but ...
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Totally Block Pulses of Smart Meter [on hold]

What to put on inside walls to totally block pulses of PG&E's four smart meters
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25 views

A steady line current moving at a steady velocity can produce non-transverse electric fields. What about moving line charges?

A steady, straight current that is stationary can exert a Lorentz force on a moving charge that is parallel to that current. Conversely, a stationary charge can experience a Lorentz force that is "...
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1answer
42 views

Do emitted photons have a well defined frequency or just a spread as per HUP?

I have read this question: Conservation of Energy in photon exchange between two atoms where Kurshal Shah in a comment says: As per the energy-time uncertainty relation, the emitted photon ...
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What is the real difference between tunneling ionization and multiphoton ionization (MPI)?

Ionization is when an EM neutral atom gaing Em charge by losing or gaining an electron. Tunnel ionization is ionization due to quantum tunneling. In classical ionization, an electron must have ...
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What is the real problem in the free body problem?

Ions are produced when an EM neutral atom gains EM charge by gaining or losing electrons, by collision with other charged particles or photons. The study of such collisions is of fundamental ...
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$B$ field inside a Magnet

From Lorentz Force law there are experimental proofs for defining the direction of the magnetic field $B$ outside the magnet. But when the interior of magnetic material is concerned how is the ...
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1answer
20 views

Poynting vector flux on a closed surface

What does the flux of the Poynting vector through a closed surface represent? I know that the flux of the Poynting vector on a certain surface represents the power flowing through it. But if the ...
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Brownian Motion of Charged Particles [on hold]

Which type of particles possess Brownian motion, Does the charged particles show Brownian motion?
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1answer
22 views

Magnetic horn function

I wonder how a magnetic horn works. I can imagine that a magnetic field will distract particles due to their charge but what I don't understand is, how to isolate antiprotons? The charge is probably ...
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1answer
26 views

Magnetic Detection of Magnetite

I have a tool with a very thin and faded coating of what seems to be magnetite black oxide ($\mathrm{Fe_3O_4}$), I’m trying to see if this coating is magnetite, while a chemical test is possible, a ...
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What is the derivation of Rayleigh's Equation? How do i get to Rayleigh's equation? [on hold]

im looking for an answer of the derivation of rayleigh's equation, ie; how to get to the equation through derivaiton, thanks
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3answers
107 views

If a constant current can create constant magnetic field , why do we need changing magnetic field to induce current?

The electrons only going from negative to positive are able to create a magnetic field, why does the magnetic field have to keep changing to induce a current? If I pass the same magnetic field through ...
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High efficiency motor design with lasers [on hold]

I'm testing theories of lasers to push/repel another object in a motor like fashion, pulses of light to push said material into rotation at high speed. Solar sail like object in a smaller format to ...
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22 views

Orientation and sign convention in 2D electrodynamics using differential forms

I've been following this paper for a treatment of electrodynamics using differential forms. In particular, they demonstrate that Maxwell's equations expressed using differential forms are form-...
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1answer
45 views

An electrodinamic identity: starting point

With this request, I would like to ask you kindly how you can prove this identity. I thank you for those who can help me. \begin{equation} \overline{\nabla} \times (\overline{\nabla} \times \...
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Naive question - Is Magnetic generator (like this) not a 'perpetual motion machine'? [duplicate]

Perhaps a question that is too naive to be on Physics.SE but I let the experts here decide (and downvote at will), but there seem to a certain company that claims to have created what it calls a "...
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Torque on a current carrying semicircular coil placed perpendicular to a magnetic field [on hold]

I found out that the force on differential elements will be radially outwards so the net torque about C will be zero but I am confused on how to find the net torque about P. I understand that the ...
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2answers
76 views

H field Vs B Field inside a magnet

I was studying electromagnetism and was going the basic definition and trying to understand their importance. I could not figure the difference between The H- Field and B- Field at first. So I ...
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how to use electricity into weight [duplicate]

I have a doubt, it is possible that electromagnetic force can be used instead of weight bars. An electromagnet is simulated as weight in real-time? if I pull 5 kg weight in the electromagnetic field ...
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3answers
28 views

Direction of EMF and Induced current through the circuit

When the circuit shown above is moved with a constant velocity to the left I know that B is going to have the higher potential. And I believe that the current flows clockwise that is in the sense of ...
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15 views

Magnetic Field Lines Vs Magnetic Vector field

I am studying electromagnetic theory and when I started researching the history of conventions used in magnetic interactions I could not get them. The basics of how they modelled the magnetic ...
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2answers
49 views

Permanent magnet attraction from Maxwell's equations / Lorentz force [duplicate]

Edit: My question is different because I am not asking how permanent magnets come about. Rather, I am asking why (taking permanent magnets as a given) they attract or repel each other. I.e. What ...
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144 views

Compact expression of Maxwell's equations: missed minus sign

With much courtesy I ask a simple explanation to be able to obtain a minus sign missing from the compact form of Maxwell's equations: $$\boxed{\square \overleftrightarrow F=\mu_0 \boldsymbol{\mathcal{...
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Best books for Electromagnetism? [duplicate]

I would like to know some titles of the best books in Electromagnetism. Some poeple recommended me to read Griffiths. My big deal is to become a theoretical physicist in Particles/Fields and ...
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Understanding of Gauss law using vector fields

I was going through the conventions and terminologies followed to describe the magnetic interactions. I understood that the field lines are just a simpler representation of the magnetic interaction ...
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Optics Questions! [closed]

Can anyone solve this please its urgent!! Related to optics.Undergrad level
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1answer
43 views

Does protons moving parallel to each other exert magnetics force

If two protons are moving parallel to each other in same direction with equal velocities then do they exert magnetic force on each other.? As protons are moving they should produce magnetic field and ...
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1answer
67 views

Newton's third law in magnetic in magnetic fields

Say I have a charged particle moving through a magnetic field perpendicular to it. It will experience a force, but according to Newton third law Every force has an equal and opposite reaction. So ...
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Time derivative of dipole moment

While deriving the relation, $$\int_V \bar{J}d \tau = \frac{d\bar{p}}{dt} $$ in this question. We have, $$\frac{d\bar{p}}{dt} = \frac{d}{dt}\int_V\rho \bar{r} d\tau \\ \implies \int _V \frac{\...
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Doubt Related To Working Of A Cyclotron

The condition good resonance in case of revolution of +ve charged particles in Dees is , Frequency Of Semi-Circular Motion Of +ve Charged Particle = Frequency Of H.F. Oscillator OR Frequency Of ...
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Poynting vector flux in a tube (geometrical optics)

Let's consider the following tube (defined as the solid described by two arbitrary surfaces dA1 and dA2, and by all the rays which connect their boundaries): I read in a textbook that, because of ...
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66 views

How to convert electricity into weight? [closed]

I have a doubt, it is possible that electromagnetic force can be used instead of weight bars. An electromagnet is simulated as weight in real-time? if I pull 5 kg weight in the electromagnetic field ...
0
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1answer
20 views

How to recover the potential field from Green's function and Poisson's equation for a point charge

I first find the Green's function for the following PDE in $n=3$ dimensions, where $k:=|k|^2$. $$\nabla^2G(x,x')=\delta^3(x-x')$$ Upon Fourier transforming both sides, and inverting, I find that $$G(x,...
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Locality sheilding material [closed]

Need knowledge of where to locate sleep sanctuary (bed canopy) hence Sydney area? EMF solutions
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2answers
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What do you see when you are inside a transparent conducting material?

Lets say that there exists a transparent conducting material. Lets carve a cavity in the meat of the conductor big enough for a person to stay in. There exists an external electric field. But, We ...
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2answers
108 views

Why doesn't a magnetic field accelerate moving charges?

As a magnetic field of intensity, $\mathbf{B}$ applies a force of $\mathbf{F}= q\mathbf{v} \times \mathbf{B}$ on a charge $q$ moving with velocity $\mathbf{v}$, this force $\mathbf{F}$ should be ...
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4answers
109 views

Electromagnetic waves according to Maxwell

If a variable Electric field creates a variable magnetic field and VICE VERSA (according to Maxwell's equations), then why don't we enter a loop where E vector and B vector keep creating one another ...