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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121 views

Motion in a Paul trap: $2n^{\text{th}}$ harmonic with larger amplitude than $n$th harmonic

Using a Paul trap, we captured the motion of a light charged particle (based on a rotating potential applied by AC current). Our rotational frequency was 50 Hz, and so when used FFT on the data, we ...
0
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1answer
38 views

Are the electrons spin and his magnetic dipole moment unambiguously connected?

Is the angle between the spin orientation and the magnetic dipole orientation for all electrons and under all circumstances the same?
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0answers
28 views

How to repeat the Biot-Savart experiment for the direct current in a straight wire and the corresponding magnetic field without side effects?

As I read Biot and Savart took a compass needle and this needle make some rotation when the current was switched on and off. As it was clear that a changing current induces a magnetic field the ...
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0answers
15 views

Expanding the H and D field in orthogonal modes

Currently I am doing my bachelor thesis on the behaviour of Q-factors in 3D microwave cavities. One step in that process is to approximate the behaviour of the 3D cavity by comparing the cavity to an ...
0
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1answer
1k views

Why magnetic field lines and force are not orthogonal with magnets?

The below explanation why magnetism exists is superb in this video. The explanation about magnets is also great in this video. A magnet has atoms with unpaired electrons forming mini magnets. The ...
3
votes
1answer
433 views

Homopolar motor and Lorentz force

My second grader thought making a homopolar motor for her science experiment would be fun. And, it was. Now I am trying to explain how it works and the Lorentz force. Please help me by giving me a ...
4
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1answer
36 views

Interference and windows

The other day i was learning about interference patterns with the effect of a bubble making a rainbow on the surface. I learned that the reflections from both sides of the soap can interfere ...
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0answers
13 views

Electromagnetism Books and Lectures [duplicate]

I am an undergraduate at mathematics.And this semester i took E&M as one of my courses because i found it interesting .So i am looking for a good introductory book that will keep my interest as ...
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0answers
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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2answers
68 views

What actually is a continuous charge distribution? [closed]

I am well aware of the maths of how to do all sorts of calculations using continuous charge distributions (like volume, space, and, line charge distributions) but when I think about it I couldn't get ...
3
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2answers
337 views

AC Electromagnets

Could someone help explain the uses of AC electromagnets. Wherever I look it says that DC electromagnets create stronger magnetic fields. I understand why AC electromagnets could be used in ...
0
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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?
7
votes
1answer
243 views

Why dimensionality of the Electric Charge varies with the spacetime dimensions?

The point is: We can find via dimensional analysis that the electric charge dimensionality varies with the dimension of space-time. $$[\text{charge}] = eV^{(3-D)/2}$$(You can see below the way I did ...
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1answer
65 views

Electromagnetic braking hypothetical situation?

Let's say there is a conducting rod in space - with a constant external magnetic field. If you spin the rod - will electromagnetic braking make the rod stop eventually? I feel like there is a change ...
1
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1answer
101 views

Free Electromagnetic field in Lorenz gauge

To get rid of the extra term in the QED Lagrangian we need to redefine the electromagnetic four-vector: $A^{\mu} \rightarrow A^{\mu} - \frac{1}{c} \partial_{\mu} a(x)$ where $a(x)$ is the function ...
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1answer
45 views

Electron propagation

How can electrons travel in these beams if they repel?
3
votes
1answer
761 views

Why is the magnetic field stronger at the edges of a bar magnet?

I have been performing an experiment at school in which I test the force on an iron surface from the magnetic field of an electromagnet. The electromagnet has a rectangular iron core. The theory ...
0
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1answer
721 views

Electric field from conductive to dielectric media

I am interested in the main difference between transitions from electric fields from Conductive to Conductive/ Dielectric to Dielectric and Dielectric/Conductive media. What are the boundary ...
1
vote
1answer
59 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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2answers
4k views

Does gravity affect magnetism, vice-versa, or do they “ignore” each other?

I am suddenly struck by the question of whether gravitation affects magnetism in some way. On the other hand, gravity is a weak force, but magnetism seems to be a strong force, so would magnetism ...
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1answer
35 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 ...
4
votes
1answer
200 views

Dielectric tensor vs. conductivity tensor in (cold) plasmas

I'm studying Waves in Cold plasmas right now, but I guess my question is generalizable. It's about the 4th Maxwell Equation in polarizable / conductive media: $\nabla \times H = \frac{1}{c} ...
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0answers
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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1answer
34 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 ...
3
votes
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
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 ...
0
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1answer
32 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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2answers
140 views

Induced emf in stationary conductor lying in varying magnetic field

We explain that motional emf is induced because charges in a conductor move along with the conductor and as a result a magnetic force pushes them to one side of the conductor. But in case of a ...
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0answers
21 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.
0
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1answer
127 views

Right hand solenoid example

I am just studying for my physics final exam. I came across this example and am not satisfied with the answer. My answer is that Z is South and the current would flow from Y to X because of the ...
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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 ...
1
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1answer
89 views

$U(1)$ 5-dimensional Kaluza-Klein topological defects

Five-dimensional Kaluza-Klein theory is well-known to predict that the electromagnetic field can be described as a curled additional dimension over four-dimensional spacetime. That is, you only need ...
3
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1answer
61 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 ...
0
votes
1answer
342 views

Coercivity of a ferromagnetic material?

I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the ...
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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.?
3
votes
3answers
282 views

How are the Lorentz force, Maxwell's third law and Faraday's law of induction clasically related?

Faraday's law of induction can be used in any situation where the magnetic flux is changing through a closed conducting loop. While giving the correct answer, it seems to me that for the following ...
0
votes
1answer
164 views

What are the boundary conditions for EM waves normally incident on the interface between two dielectric media?

An EM wave, amplitude $E_0$, frequency $\omega_0$, is incident upon a material with relative permittivity (dielectric function) $$\varepsilon \left( z \right) = \left\{ \begin{gathered}{\varepsilon ...
0
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2answers
371 views

Torque per unit length on infinite rotating charged cylinder

For homework I have the following question, but I am stuck on finding the torque on the cylinder. An infinite cylinder of radius $R$ carries a uniform surface charge $\sigma$. We start rotating the ...
0
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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 ...
0
votes
1answer
27 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 ...
8
votes
3answers
593 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.
1
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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.
1
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1answer
76 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 ...
0
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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 ...
0
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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 ...
1
vote
1answer
69 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 ...
0
votes
1answer
46 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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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 ...
5
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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 ...