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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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5answers
9k views

How do we know neutrons have no charge?

We observe that protons are positively charged, and that neutrons are strongly attracted to them, much as we would expect of oppositely charged particles. We then describe that attraction as non-...
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0answers
12 views

Velocity attained by a Loop with an induced current

A rectangular loop of resistance R is kept at a certain distance from an infinite straight current carrying conductor. The current is suddenly switched off. The problem was to find the velocity ...
1
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2answers
68 views

In the Stern-Gerlach experiment, why is there a nonzero force even though the atoms were electrically neutral

I know that the magnetic moment of a particle is given by: $\vec{\mu} = \frac{gq}{2mc}\vec{S}$ I know that in the Stern-Gerlach experiment, neutral silver atoms were used. Additionally, the ...
0
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1answer
31 views

Explanation on the current circulation in a circuit

I'm studying the electromagnetsim, and I couldn't find a complete explanation on how the current flows in a circuit; I mean, basically, how do I decide whether the current is flowing in or out a node? ...
0
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2answers
41 views

What really is an electric/magnetic field?

Have you ever wondered how we can see this field or how it's formed its shape in space? I know we can feel that there's one by its effect which is the force. But what does it look like? We all know ...
0
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0answers
19 views

Detecting particles that do not make it through double slits, do observations match those after the slits?

I suppose we have 4 conditions to examine : { single particle | beam } * { with eraser | without eraser } I suppose we have to get the same results that those ...
0
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0answers
14 views

Calculation of Lorentz force acting on a volume

Consider a volume $V$ immersed in a magnetic field $\hat B$. Assume that within the volume a current $I$ flows such that the surface density at each surface of the horizontal cross section of the ...
0
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1answer
43 views

Electromagnetic waves, displacement currents and capacitors

This is a question from HC Verma’s concepts of Physics Vol 2: Electromagnetic Waves. It’s a question which is a continuation of the previous question, therefore I’ve combined both of them. Q. A ...
0
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0answers
28 views

Can EM radiation penetrate through the walls of an aluminium box (Faraday cage)?

What's the best possible frequency to use and is it high frequency or low frequency that has the highest ability to penetrate an aluminium wall?
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0answers
20 views

How to calculate the RCS (Radar Cross Section) of a sensor tag?

The equation for finding the RCS of sensor tags is given in the following paper. where $S_{21}^{tag}$ stands for the $S_{21}$ measurement taken for the tag in front of a reader. $S_{21}^{isolation}$ ...
0
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1answer
55 views

Why aren't primary and secondary coils of a transformer overlapped over each other? [closed]

I am aware that soft iron core present in a transformer does prevent flux leakage. But practically there is some non-negligible flux leakage nonetheless. Why not then just overlap the coils over each ...
0
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0answers
13 views

E.M field in a cavity having mirrors : Periodic boundary conditions vs strict periodic boundary conditions

I have a question about how work with modes in a cavity. Basically, why are we allowed to use periodic boundary conditions (and thus plane waves) where in practice the modes are stationnary waves. Why ...
0
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1answer
24 views

Strength of Magnetic Dipole

I know magnetic monopoles doesnt exists .And A magnetic dipole always have equal strength. But what about this magnet This is picture of magnet whose thickness is constantly decreasing Will it have ...
0
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1answer
31 views

Irradiation at high frequency

I read this statement in Feynman Lecture on Physics (see here for more details): In low-frequency circuits the connection is made with wires, but this method doesn’t work very well at high ...
0
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2answers
41 views

Electrical generators: power balance

Usually power generating synchronous generators are rated at around 85-90% efficiency. Curiosity struck me as of how a generator with field coils can ever go to such an high efficiency. My thought ...
0
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2answers
46 views

How can a spring contract when magnetic field cannot do work?

When a spring is kept in a magnetic field and current is passed through it, its edges act as parallel conductors and due to the action of Lorentz force, they pull themselves together. A spring ...
0
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1answer
24 views

Amplitude of EM waves

I'm trying to calculate the Amplitude of electric field in the EM waves using the differential forms from maxwells equations. I've been given frequency ($10^8$ Hz) and displacement current density ($...
0
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1answer
35 views

Electric Field inside an ideal conductor

I have some doubts about the electric field inside an ideal conductor (let's call it E). Precisely, I have read two different descriptions 1) On physics books I read that the electric field inside in ...
0
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2answers
35 views

Why does ohms law not work on transformers? [duplicate]

The voltage for transformer is given by $\frac{V_1}{V_2} =\frac{N_2}{N_1}$ if we use ohms law and assume resistance are same for both inductors, $\frac{I_1 R} { I_2 R}=\frac{N_2}{N_1}$ but in my ...
0
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1answer
39 views

Unable to follow Feynman Lectures reading on opacity

Feynman is explaining the phenomenon of opacity in terms of classical electrodynamics. Let us first ask: “What is an opaque screen?” Suppose we have a completely opaque screen between a source S ...
0
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1answer
32 views

Why is it not good to use a waveguide at low frequencies?

Which is the physical phenomenon behind this?
0
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1answer
38 views

Electric Potential Outside of Two Infinite Sheets of Opposite charge density

If you have two infinite sheets of equal but opposite charge density, the electric field outside the sheets will be zero due to cancellation. This led me to initially think that the potential would ...
0
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2answers
39 views

Visualization of electromagnetic waves with potentials?

I wonder if there is out there any visualization of the propagation of electromagnetic waves, not only with the electric and magnetic fields components but an actual visualization of the underlying ...
0
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1answer
33 views

What causes a steel gurney to accelerate towards an MRI machine? [duplicate]

What is the basic concept in electromagnetism that explains the MRI projectile effect in which steel objects such as gurneys crash into an MRI machine with a force that is sufficient to kill or ...
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2answers
49 views

Does action at distance in electromagnetism violate energy conservation?

Consider two charges A and B separated at distance D. charge B is attached on spring and can move towards and away from charge A. Now charge A is brought closer to charge B and then it is taken back ...
0
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1answer
9 views

What is responsible for large ppm shifts in HNMR analysis of paramagnetic compounds?

In H-NMR spectra of paramagnetic metal acetylacetonate compounds M(III)(acac)3, large ppm shifts are observed. This is seen with other organometallic compounds as well. What is the origin of this ...
3
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2answers
90 views

Physically intuitive explanation for Hamiltonian of charged particle in EM field

I've recently been looking at the quantum mechanical description of a charged particle in an EM field and have come across this classical Hamiltonian: $$H = \cfrac{(\mathbf p - q\mathbf A)^2}{2m} + q\...
2
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3answers
78 views

What was the energy of light thought to be before Einstein

I'm studying the photoelectric effect where it turned out that the kinetic energy of the emitted electron was dependent on the frequency of the u.v. light and not its intensity. It was previously ...
2
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1answer
39 views

Current induced from a changing magnetic field

This question is motivated by Problem 7.12 in Griffiths Electrodynamics book. I have already solved the question, so there is no issue with homework policy. Relevant Equations: $$\Phi = \int{\vec{B}\...
1
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2answers
53 views

Showing $\partial_{\mu}\tilde{F}^{\mu\nu}=0$ by the antisymmetric properties

The electromagnetic dual tensor is given by \begin{align} \tilde{F}^{\mu\nu}=\frac{1}{2}\epsilon^{\mu\nu\delta\rho}F_{\delta\rho} \end{align} Here, $\epsilon^{\mu\nu\delta\rho}$ is the Levi-Civita ...
0
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1answer
18 views

No commutator or rectifier?

Homopolar motors and generators don't need a commutator or rectifier. Are there any other motors or generators that don't need a commutator or rectifier? If so, what are they?
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0answers
26 views

What is the phase relationship between current and magnetic field?

I understand the phase relationship of the electric and magnetic fields. but what is the phase relationship between current in an inductor and magnetic field produced due to this current?
0
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2answers
30 views

Confusion about magnetism in a circuit breaker

Why should the core of a coil of a circuit breaker be strongly magnetized when current passes through it, and immediately demagnetized when the switch is turned off? Please try to explain the ...
0
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1answer
49 views

Phase difference

Is there a phase difference between the magnetic field and the current producing this field? I have simulation results for three-phase transformer at different frequencies. The spectrum of the ...
0
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0answers
18 views

Turn density impact on B Flux

I am messing around with electromagnets and I am actually making my own winding them by hand. The equations that are used to calculate magnetic field strength do not really have a geometry term in ...
-2
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1answer
38 views

Acceleration through potential difference [closed]

Fe^1+ ions are accelerated through a potential difference of V volts. What does this statement even mean???Please explain it to me. And please give me a general formula to work out the velocity ...
0
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0answers
47 views

Deriving the Maxwell Scalar field Equation from the given action principle

I am currently starting to learn general relativity. I have been trying to derive the Maxwell Scalar field equation from the given action $\mathcal{S}[\phi, A, \mathbf{g}]=\int\left(\frac{1}{2}\left(\...
2
votes
2answers
181 views

Does a magnet moving in a uniform electric field experience torque?

Assume a uniform electric field of $E_y$ along $y$ in the lab frame of reference $(x,y,z,t)$. A simple magnet bar is set in motion at $v$ along $x$ in this electric field so that the alignment of the ...
4
votes
0answers
34 views

Variation of phase across the wavefront

I have been going through the theory of diffraction of radio waves when passing through the ionosphere, when I came across the following statement: the amplitude of the wave when it emerges from ...
-1
votes
1answer
33 views

Magnetized Steel wire around Soft Iron Core

We all know that a current carrying solenoid of copper is a weak temporary magnet and if we wrap it around a soft iron core it becomes a temporary strong magnet i.e. the iron core magnifies the ...
3
votes
1answer
48 views

Why does the interaction energy for the electric fields of two point charges vanish over any shell smaller than their separation?

A previous question, A triple integral in Spherical coordinates from Jackson's book on Electrodynamics, presents the fairly routine calculation of the interaction energy encoded in the cross-term ...
-2
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1answer
50 views

Gravitational and Electric Forces in the Movements of Planets [duplicate]

Now that we know about the electric nature of the cosmos, the question arises: "How much are planets affected by electric forces while moving through the universe?" We have been taught that the ...
1
vote
1answer
96 views

A triple integral in Spherical coordinates from Jackson's book on Electrodynamics [closed]

I have been trying a solution for the following integral from Jackson but i do not seem to go anywhere. Please help. The problem is to compute interaction energy due to 2 charges. Compute following ...
0
votes
1answer
27 views

Inductors in Transformers

Why is it the flux change which induces the ac current of primary coil equal to the flux change that primary coil induces on the secondary coil? Is it possible to prove this? slide from video ...
-4
votes
1answer
74 views

What does $e$, $i$ and $\vec{p}$ mean in this formula? [closed]

I've found a formula to calculate the $\vec{E}$-field vector of a Hertzian dipole in the far field (don't know if that's the correct term) to draw and simulate the field lines. Link to my source: ...
1
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3answers
33 views

How to relate magnetic flux to fluid flux?

I'm trying to grasp magnetic flux as an analogous concept to fluid flux, which is more concrete in my opinion. For example, we can define a vector field $\mathbf{F}(x, y, z)$ which describes the ...
0
votes
1answer
34 views

Magnetism problem

I encountered a magnetism problem requiring me to find out the minimum velocity (along $\hat{\mathbf{i}}$) given to a charged particle so that it passes through the centre of a circular region of ...
0
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0answers
15 views

How are the two definitions of B, as magnetic field and magnetic flux density, same?

My question, is primarily, based on this question, in which the accepted answer asserts that $\vec B \, $ has two definitions, As magnetic field$^*$, using Lorentz force $\vec F=q \vec v \times \vec ...
0
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2answers
42 views

Do photons influence charged particles? [duplicate]

As a neutrally charged particle, a photon shouldn't interact electrically with another charged particle. However, since photons are electromagnetic waves, they should interact with charged particles, ...
0
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0answers
47 views

Contact potential between metals

Metals Al and Au are connected in series. An ideal voltmeter, with both of its leads made of Cu, is connected across them. Then how come the voltmeter gives zero reading but why can't we measure ...