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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21 views

Accurateness of measurement of 1Ampère for the last years, especially depending from the method how to switch on the current?

From Wikipedia: Ampère's force law states that there is an attractive or repulsive force between two parallel wires carrying an electric current. This force is used in the formal definition of the ...
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1answer
29 views

How does the Hutchinson Effect work? [closed]

I have seen pictures online of metal ripped apart and metal completely messed up due to the Hutchinson Effect. How does this effect work and what are the other principles behind it?
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1answer
44 views

Electron propagation

How can electrons travel in these beams if they repel?
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1answer
32 views

How does the magnetic field generated from a rectangular cross-sectional current-carrying conductor differ from a circular cross-sectional conductor?

I can find much information of cylindrical conductors (ie. regular wires), where $B=\frac{\mu_0 i}{2 \pi r}$ and $r$ represents the radius (or distance) from the centre of the conductor, however I ...
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1answer
58 views

Why particles don't lose mass when they radiate

Charged particles radiate when accelerated: in the rest frame of the particle moving with acceleration $\textbf{a}$ the amount $dW$ of radiated energy over time $dt$ is $$ dW \propto \textbf{a}^2 ...
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1answer
33 views

Explanation for: A monopole antenna must contain a resistor (or equivalent) and therefore must have 2 terminals?

Could someone explain why this sentence makes sense: A monopole antenna transfers energy from electrical domain to the electromagnetic domain, hence must contain (equivalently) a resistor, hence ...
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13 views

Reference for the Definition of Magnetic Properties [duplicate]

I am writing a report on a piece of software I have made as part of my final year assessments. The software models the flux density of arbitrary arrangements of permanent magnets. The readers of my ...
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0answers
32 views

Speed of light in a medium as superposition of dipole radiation

Studying electromagnetism I know that the speed of light in a medium is $v = c/\eta$ and that it's possible to derive this from the Maxwell equations in the medium. But I wanted to find a microscopic ...
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1answer
45 views

What is the difference between a magnon and a spinon?

For a long time, I thought the terms "magnon" and "spinon" were equivalent, describing the collective spin excitation in a system. Lately, I have seen remarks in the literature that they indeed do ...
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0answers
20 views

How to generate a Hysteresis curve using MOKE?

I am designing an online lab to generate Hysteresis curve using the principles of MOKE (Magneto Optical Kerr Effect) Is there any math or a logic that I can use to generate the Hysteresis curve? ...
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0answers
25 views

What are some good online texts for electromagnetism? [duplicate]

I am trying to gain a basic knowledge of electricity and magnetism. The resource being free/cheap is important, because I am still a high school student and don't have much money to spend on books.
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1answer
31 views

Proof the directivity antenna formula in degrees

For a single-lobed pattern the beam solid angle is approximately given by $$\Omega_A \approx HP_E.HP_H$$ where $HP_E$ and $HP_H$ are the half-power beamwidths in radians of the main beam in the E ...
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1answer
187 views

Charged particle under a uniform electric field

Suppose a charge particle $q$ starts to move without initial velocity under the influence of a uniform electric field $E$ pointing in the positive $x$ direction. Express its position vector in ...
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0answers
8 views

Carnot cycle efficiency increases by which method either increase sink temp. or decrease source temp

which method is more suitable for increasing efficiency of Carnot cycle engine either increase sink temp. or decrease source temp.?
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1answer
52 views

Magnetic field and electric field induce one another forever [duplicate]

A changing electric field produces magnetic field and vice versa. Does that mean that this process will carry on forever? Think of a circuit with a capacitor. The magnetic field due to the current at ...
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0answers
15 views

Two circles in uniaxial anisotropy and remanence plot?

I am thinking how you can show that there are two perfect circles separated by $\delta$ in an uniaxial anisotropy with the material CoFeB; here a draft practical case data about them The general ...
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1answer
26 views

What is the force on a moving charge in combined magnetic and electric fields, in general, when the magnetic field defines the z-axis?

This is a question from a problem sheet. How am I supposed to find the force applied to a moving charge by magnetic and electric fields when the question only gives me the magnetic field $B=B_z \hat ...
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1answer
60 views

Induced magnetic field produces electric field and vice versa forever!

So here are the two of Maxwell's laws that I am interested in: So we have the simple circuit (from google): So, before the system goes into steady-state we know that charge slowly accumulates on ...
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3answers
590 views

Would a spinning, evenly charged sphere generate a magnetic field?

I could see how it would go either way. On the one hand, there IS moving charge; on the other hand, it is not discernibly moving.
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2answers
41 views

Is there an electric field due to current?

Is there any electric field associated with current? If yes, then charge particle passing through magnetic field due to current should also experience electric force along with magnetic force.
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1answer
75 views

Why is gravity viewed as a curvature of spacetime and not the electromagnetic force? [duplicate]

There are four known forces in the universe. Two of these forces are the force of gravity and the force of electromagnetism. The first is the result of the mass of the object that has the gravity. The ...
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0answers
52 views

Why is the electric field inside a solenoid tangential?

I have been looking at some derivations for the electric field inside a solenoid. I know how to find it, but I don't get the symmetry argument used. This is often of the form: Since if we choose ...
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0answers
11 views

Can TEM waves have constant offsets - that is, mean of non-zero in context of Poynting's theorem?

Suppose the electromagnetic wave and the corresponding magnetic field wave are TEM waves. Can such waves have overall mean of non-zero? (so DC offset) If they do, what do they mean in context of ...
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1answer
67 views

Finding Magnetic Field in loop of wire in semicircle [closed]

This is the problem I'm working on: A loop of wire has the shape of two concentric semicircles connected by two radial segments (See figure). The loop carries a current $I = 280.00 A$. Find the ...
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1answer
44 views

What do we mean with magnetic monopole and dipole?

What do we mean with magnetic monopole and dipole? I can not find a way to relate magnetic monopoles and dipoles with electric ones. I do not understand their outcomes. Also,what is their role in ...
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1answer
49 views

Induced potential difference paradox

So,i was studying from some lecture notes from MIT's open course program,and i stumbled across this example The example says:The solenoid is so long that its external magnetic field is negligible. ...
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2answers
44 views

Induced emf problem

This is not homework question,just a thought experiment about a general question i have about induction. Let's suppose that we have a closed circuit with only two resistors in series.We also have a ...
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0answers
23 views

Induced EMF question. Not sure what I'm doing wrong. [closed]

The question: A circular conducting loop of radius 17.0 cm is located in a region of homogeneous magnetic field of magnitude 0.100T pointing perpendicular to the plane of the loop. The loop is ...
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1answer
37 views

Why is it possible to define a potential difference in a wire that carries a steady current?

My book introduces $\nabla\times E = 0$ as the condition for an electrostatic field, which is what makes it possible to define a potential difference between two points. As far as my present ...
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0answers
55 views

Magnetic force between two point charges

I tried to derive the magnetic force between two point-charges for iterative computation. Starting out with Lorentz force and Biot–Savart law for a point charge. $$ \vec F = q_2( - \Delta \vec{v} ...
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3answers
54 views

What is the direction of the magnetic vector potential in an electromagnetic plane wave?

The vector potential $A$ is perpendicular to $B = \nabla \times A$, by definition, and hence, in a plane wave, it is either in the direction of $E$ or the direction of propagation. I suspect it is in ...
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4answers
119 views

Non-complex proof that the electric and magnetic fields are perpendicular in a plane wave

I'm looking for a proof that the electric and magnetic fields in a plane wave are perpendicular that doesn't invoke complex E and B fields. I haven't been able to find one. If the proof requires ...
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0answers
21 views

Perpendicular Current Carrying Wires Forces?

Hi guys, I'm having trouble understanding the effect of sides BA and CD on the straight wire. With an amperian loop around the straight wire, the magnetic field on BA and CD is into the page, and ...
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3answers
624 views

Why should Conservative forces have their curl equal to zero?(intuition)

There are several conditions that must be met in order for a force to be conservative. One of them is that the curl of that force must be equal to zero? What is the physical intuition behind this? If ...
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2answers
34 views

Electric Field At Centre Of Non Uniform Ring

In the above solved example why only the cos components have been taken for calculation of electric field at centre ? Why not the sine components ? BTW in case you say that the sine components ...
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0answers
26 views

Magnetic field of cylinder equal to two current loops?

I was reading a text about the magnetic field of a uniformly magnetized cylinder when I came across this. The author states that since \begin{equation} A_{\phi}(\rho,z) = \frac{\mu_0 a M}{4\pi} ...
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0answers
20 views

Electromagnetic boundary conditions for modelling symmetrical geometry

I stumbled upon this article: http://www.comsol.com/blogs/exploiting-symmetry-simplify-magnetic-field-modeling/ Since the article does not contain any mathematical formulations, I was wondering how ...
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3answers
145 views

What would it take to cause lightning to jump between the Moon and the Earth?

This question comes from @Floris' speculation at the end of his excellent answer about what it would take to kill everyone on the Earth with electricity. Doing all this in 1/10th of a second ...
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0answers
7 views

Relationship between plasmon resonance frequency and radius for small nanoparticles

Is there any literature that gives a functional relationship between plasmon resonance frequency and radius for small spherical nanoparticles (on the order of 10nm or less). I can't seem to pin down ...
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1answer
32 views

What is the difference in the behaviour of the commutator in a motor between DC and AC?

Is it correct to say that in DC, the split ring commutator produces direct current flow and therefore stronger voltage, as opposed to AC which produces alternating current and therefore weaker ...
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0answers
20 views

Is the electron's magnetic dipole moment influenced by the measurement method?

The electric charge of an electron at rest is a constant value and is not influenced by the measurement instrument. The measurement instrument by itself can give more or less accurate result, but does ...
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2answers
49 views

Is it possible to make an electromagnetic shield?

Is it possible to make an electromagnetic shield to protect something (or ourselves) against things like bullets, human attacks, metals thrown on us or simple dust particles to protect a spaceship ...
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1answer
51 views

Right hand rule confusion

I have a question that I am trying to figure out: Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right ...
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1answer
43 views

The Electric Quadrupole

I've read the following sentence: "Every electric circuit with two pairs of accessible terminals is called a quadrupole." I was wondering why does it happen that the multipole expansion gives us a ...
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1answer
64 views

Force between two finite parallel current carrying wires

Remark: This is not a homework question...It is pure out of theoretical interest. I asked this the mathematics-community a couple days ago and got no answer, so I figured I'd try here. Most standard ...
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1answer
16 views

squared position dependent electric field [closed]

Here's an asignment problem that got me puzzled. The thing is that I have to solve a second order non linear differential euqation, the course is an urdergraduate mechanics course. A particle of mass ...
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1answer
113 views

Using a circuit to make a magnetic balance to weigh objects

I understand that this is a homework question, but I am learning about magnetic fields and things like that and this certainly wasn't covered in the material, so my question is more about the actual ...
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1answer
44 views

magnetic field due to current in a wire using Biot-Savart's law

I am learning about Biot-Savart's law to calculate the magnetic field due to the electric current in a wire. ...
3
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1answer
70 views

How much magnetic field will be required to levitate a human? [duplicate]

According to this video: https://www.youtube.com/watch?v=BqKeiiezqzc it should be possible to levitate humans because the water in our bodies is diamagnetic - but it is stated (at 1:14) "although ...
3
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1answer
95 views

When (or what is the meaning of) $I \propto E^2$?

For a monochromatic plane wave: $$\mathbf E = \mathbf E _0e^{i(\mathbf k \cdot \mathbf r -\omega t)},\qquad \mathbf H = \dfrac{\mathbf B}{\mu _0}= \mathbf H_0e^{i(\mathbf k \cdot \mathbf r-\omega ...