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.

learn more… | top users | synonyms (6)

-2
votes
0answers
50 views

I need a book to deeply understand electromagnetism [duplicate]

i am an electrical engineer and i want a deeper understanding of electromagnetism, something beyond the equations, i am looking for something the "Theoretical Minimum" book but for electromagnetism. ...
0
votes
1answer
152 views

magnetic field of a rotating ring magnet

Can the magnetic field of a rotating ring magnet induce current in a conductor? Is there a flux linkage between magnetic field of a rotating ring magnet and a conductor?
0
votes
3answers
108 views

Induction on a circuit with switch

I have the following circuit: It is subject to a steady, time-invariant magnetic field which points out of the paper. At $t = 0$, the switch closes. I thought that the magnetic flux would decrease ...
0
votes
2answers
228 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 ...
1
vote
2answers
137 views

Does a magnetic field sustain a current in a loop?

A particular current produces a constant particular magnetic field. If the fact holds under scrutiny, why doesn't a magnet held within a loop sustain a particular current? Are the electron spins ...
1
vote
0answers
22 views

Recommended books that describe emission and absorption of light and light/matter interactions

Hello I am a Chemical Engineer that has ventured into the field of optics and I was wondering if there is any recommended book/books to understand the maths and also some answered exercises or ...
0
votes
0answers
42 views

How can electric and magnetic fields have any component in the direction of propagation of electromagnetic waves?

In case of waveguides we talk about $E$ and $H$ having non zero component in the direction of propagation of wave. But the entire basis of EMW is that $E$ and $H$ are perpendicular to the direction of ...
3
votes
1answer
164 views

Magnetic Levitation : Confusion with Lenz's Law

Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an ...
1
vote
1answer
59 views

The truest/most general Maxwell's equations in isotropic, linear, inhomogeneous media with sources

Sources use $\mu H=B$ and $\epsilon E= D$, assuming homogeneous media. Obviously if $\mu$ is space varying, $\nabla . (\mu H)$ need not be equal to $\nabla . B$ What is the most general form for ...
0
votes
0answers
20 views

Correlation of magnetic field range to induced current?

If a magnetic field($B$) is increased in range(size of coverage,or flux area is larger)at the same strength, would there be higher output of current if there is a conductor with velocity($v$) passing ...
2
votes
1answer
66 views

Does charge bend spacetime like mass? [duplicate]

Does charge bend spacetime like mass? I'm not asking if electromagnetic forces can be described geometrically, but if EM fields could correspond to particular curvatures of spacetime, like gravity ...
0
votes
0answers
19 views

Electromagnetic transfer function

In a paper on the superlens, I came across the term of "transfer function". I understand that the transfer function relates the output to a given input, but I've been unable to find a formula for the ...
0
votes
0answers
15 views

Poisson Spot vs. Shadows

In textbooks, whenever I read about the Poisson spot, it involves a disk, and having light waves diffract around it and interfere constructively in the center. At the same time, when I read about ...
0
votes
0answers
30 views

Developing an analytic equation set for a complicated solenoid

So, I'm a bit stumped by this. I've been asked to develop an analytic function for the magnetic field of a complicated axisymmetric solenoid with free parameters to be determined by making a fit ...
-4
votes
1answer
56 views

Can the fundamental dimension of Electric Charge be Mass only? [closed]

After solving dimensions of electrical equations, I found out that the fundamental dimension of Electric charge is mass only. This also leads to the derivation of dimensions of other Electrical units ...
4
votes
1answer
112 views

Earnshaw Theorem for ionic solids

Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable? How can I reason this based on Earnshaw's theorem?
0
votes
1answer
225 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
votes
1answer
385 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 ...
3
votes
1answer
42 views

The role of amplitude, frequency, and intensity in mechanical vs. EM waves

As far as I know (correct me if I’m wrong), for a mechanical wave (e.g. sound), the frequency determines the pitch, the amplitude determines the loudness, and the amplitude is proportional to the ...
0
votes
1answer
199 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 ...
2
votes
4answers
768 views

Electromagnetic wave reflection vs. light reflection

Related: x-ray interaction with atmosphere I know that electromagnetic waves of particular frequencies reflect from the ionosphere. And the light (which from one perspective is an electromagnetic ...
3
votes
0answers
31 views

Physical cause of Negative Permittivity

What is the physical cause behind a material having a negative real part of its dielectric function? Given the complex permittivity, $\epsilon(\omega)=\epsilon(\omega)'+i\epsilon(\omega)''$, the Drude ...
0
votes
1answer
162 views

Computing energy loss for a hysteresis curve

Let a hysteresis loop be as shown in the figure, with $B_0$ the applied external field due to a current $I$ in a toroid, and $B_M$ the additional field due to the ferromagnetic material. Hence we ...
0
votes
1answer
50 views

Why can't two charged particles know about each other's presence instantaneously?

Why can't two charged particles know about each other's presence instantaneously? Does such a state of affairs produce contradictory or counter intuitive results?
0
votes
0answers
16 views

is there any element or material that ionized when pressure is applied to it?

I want to know if there is any material, that produce free electrons and ions when it undergoes to high pressure.
2
votes
1answer
173 views

Problem on Einstein - de Haas experiment

I am a Physics student (4th year) and I'm trying to study the Einstein - de Haas effect in laboratory. That is what I got: a suspended Iron cylinder with about 5 cm height and a radius of 0.8 cm is ...
0
votes
0answers
30 views

Two equal charges accelerating parallel to each other

Let's say constant acceleration for simplicity. Ignore possible logistic concerns, such as what is accelerating them or how they stay in path. Lets just assume they are in a conduit made of a solid ...
2
votes
1answer
134 views

Magnetic field of a static disk magnet

I have a magnetic disk (Radius R, height h) that creates magnetic field lines (axisymmetrical). I simulated the field lines, exported the data and am now trying to fit a function into the data to have ...
2
votes
3answers
324 views

Why is the inner product between divergence-free current $\vec{J}$, and a gradient field$\nabla \varphi$ zero?

I read an article saying that the inner product between divergence-free current and a gradient field is zero. A divergence-free surface current is $\nabla\cdot\vec{J}=0$, and $\vec{J}$ could be ...
3
votes
2answers
109 views

How can magnetic fields have energy and yet be unable to do work with that energy? [duplicate]

Magnetic fields can't do work. However, we use the following equation to describe the energy density of a magnetic field. $u = \frac{B^2}{2\mu_0}$ The term energy density suggests that the magnetic ...
3
votes
2answers
174 views

What is the area in Faraday's law if we have only a piece of metal moving in a magnetic field?

If a piece of metal of length $l$ is moving with a speed $v$ in a region where there is a uniform magnetic field $B$ perpendicular to it, there will be a potential difference across its terminals ...
1
vote
1answer
283 views

Remote EEG detection / reading

I recently noted that Philips, Accenture, and Emotive grouped together to create a proof of concept that would assist ALS patients to gain greater control of their lives through brain, voice, and eye ...
6
votes
3answers
25k views

In electrostatics, why the electric field inside a conductor is zero?

In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero. I ...
1
vote
2answers
403 views

Frequency of rotating coil

Given a coil initially in the x-y plane, rotating at angular frequency $ \omega $ about the x-axis in a magnetic field in the z-direction. This uniform time varying magnetic field is given by $B_z ...
1
vote
0answers
32 views

Transfer function of a space varying wave equation

$$\frac{\partial ^2 \psi}{\partial x^2}-\mu \epsilon \frac{\partial ^2 \psi}{\partial t^2}-\mu \sigma \frac{\partial \psi}{\partial t}=0$$ Is the wave electromagnetic wave equation in lossy, source ...
0
votes
2answers
2k views

Potential energy from opposing magnets repelling each other with a gap of 1 mm

I have two powerful rare earth magnets, that are separated by a distance of 1 mm. I applied energy to bring them closer to each other, hence increasing the potential energy. Now, when one of the ...
1
vote
1answer
106 views

Repelling a weak permanent magnet with an electromagnet

I have a question about magnetic repulsion. Suppose I have a permanent magnet (axially magnetized) placed on top of the iron core of an electromagnet. I want to switch on the elctromagnet to repel the ...
3
votes
2answers
209 views

Why is there no induced electric field in the experiment (Faraday's Law)

Below are three circuit diagrams for each of Faraday's experiments that allowed Faraday to come up with Faraday's Law. In Griffiths' Introduction to Electrodynamics Griffiths states (on page 302 of ...
1
vote
2answers
138 views

Energy conservation in electrodynamic system?

Consider two charged particles initially at rest in the configuration below. Let us assume the following: Starting at time $t=0$, we apply a constant force $f$ to the the bottom particle so that ...
1
vote
1answer
102 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 ...
0
votes
0answers
24 views

Magnetic field due to current carrying sheet

I have 2 infinite plates (x direction) with the width of A (y direction) and the distance between them is d (z direction). The current density is J on the first plate and -J on the second (the ...
1
vote
1answer
171 views

Work functions of ceramics/insulators

Is anyone aware of or know of a good source or means of estimating the work function of a ceramic material? Typically, work functions are given for pure elemental metals, rather than for compounds, ...
3
votes
4answers
91 views

How does an inductor store magnetic energy?

I am trying to figure out what the potential energy of an inductor with a current really means. In a capacitor, the energy stored works like this: if you let the plates attract each other, before ...
0
votes
1answer
369 views

How to calculate flux density in a toroidal CT that has an electrical line pass through the center?

I have seen the Biot–Savart equation, but I don't know how to apply it. Does the conductor length need to be considered finite and equal to the core length, or will the calculation be for a conductor ...
1
vote
1answer
39 views

Why the whole wire moves when lorentz force acts?

We know that magnitute of lorentz force is directly proportional to the current in the current carrying wire. But since the force is acting on the charges,shouldn't they get exited or thrown out when ...
0
votes
1answer
85 views

Can electromagnetic fields be used to deconstruct and reconstruct molecular bonds?

I was thinking one day and came up with a theory after reading about how scientists were studying anti-matter by using electro magnetic fields to separate matter from the anti-matter they made. It got ...
-2
votes
0answers
41 views

solving an electromagnetic problem in the frequency domain

I study a course in electromagnetic fields and I don't understand why when I solve a problem in the frequency domain I lose the transient solution. can anyone show me mathematically why does it ...
-2
votes
0answers
53 views

How it is predicted, that a moving charge has to have a magnetic field?

This question appears after this comment: Even electric charges without intrinsic magnetic dipoles moments produce magnetic fields when they move. My respons: All electric charges (electron, ...
3
votes
1answer
125 views

Is it possible to eliminate Van der Waals interactions?

I came to know that the friction force actually depends on the surface contact area due to weak interactions (adhesion due to Van der Waals forces) between the atoms of both materials increasing in ...
1
vote
4answers
131 views

Do moving charges produce magnetic fields?

As I understand it, a moving charge produces a magnetic field. Now it may be that I have have a misunderstanding here and if so I need to have the proper understanding of this. So if I do have a ...