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 (5)

11
votes
2answers
4k views

How does reflection work?

In Newton's model of light as being composed of particles, it's easy to imagine reflection as being the rebounding of individual corpuscles off a surface. However, since light can also behave like a ...
0
votes
1answer
194 views

My computer turns on when it “sees” me [closed]

Before asking, I swear that, for how it may seem strange, this is all true. Very briefly, when my pc is off and I am near it, it turns on. I do not touch anything. Nobody else have the same effect. I ...
3
votes
1answer
589 views

Measuring the vacuum permittivity

So I was reading the EF experiment that's used at the MIT to measure the vacuum permittivity and I was thinking about trying it just to see how it works: ...
2
votes
1answer
235 views

What stochastic process is associated with spontaneous electromagnetic radiation?

Imagine one have an ideal sensor, which can convert the emission to some kinds of signal (typically, voltage, and suppose no noise at all), then what process can describe the measure data? Is it ...
1
vote
2answers
148 views

A question on a system of particles governed by laws of gravity and electromagnetic field

Consider a system of many point particles each having a certain mass and electric charge and certain initial velocity. This system is completely governed by the laws of gravitation and electromagnetic ...
2
votes
1answer
315 views

Are inductance and self-inductance synonyms?

Wikipedia mentions that the word self in the word "self-inductance" is to differentiate it from "mutual inductance". But it does not state whether the two things are the same thing. So do the both ...
6
votes
0answers
267 views

1-form formulation of quantized electromagnetism

In a perpetual round of reformulations, I've put quantized electromagnetism into a 1-form notation. I'm looking for references that do anything similar, both to avoid reinventing the wheel and perhaps ...
2
votes
1answer
320 views

What will happen when we cool the permanent magnet?

When we are cooling the permanent magnet what property of magnet changes? normally the superconductivity of magnets occurs at critical temperature(negative degrees).It is having a long life period and ...
1
vote
0answers
483 views

Can we increase the magnetic flux for a permanent magnet?

When we pass current to the permanent magnet does its magnetic flux, magnetic property of attraction and repulsion increases? if possible Is there any other way for increasing the magnetic flux?
1
vote
2answers
608 views

What is the difference between north and south magnetically?

Is there a reason that magnetic field lines are drawn from north to south or is this a purely arbitrarily defined protocol (for convenience)? Essentially what I am asking is: without a reference ...
3
votes
5answers
4k views

Figuring out North and South Magnetic Poles for Earth

I currently make my living as an electrophysicist, so am a bit embarassed at having not thought this one through, before. Magnetically, the North pole is.... North. We get out our compass, and wait ...
3
votes
3answers
298 views

Singularity-free stationary electro-vacuum solution

Let's say we have a spherically symmetric fluid: $$ T^{\alpha \beta} = \begin{bmatrix} \rho & 0 & 0 & 0 \\ 0 & p & 0 & 0 \\ 0 & 0 & p & 0 \\ 0 ...
3
votes
3answers
5k views

Does a magnetic field arise from a moving charge or from its spin, or both?

I learned that a moving charge creates a magnetic field perpendicular to its direction of motion. I also learned that charged particles like electrons have spin and they also create a magnetic field ...
0
votes
1answer
493 views

How is a magnetic field translated into physical force?

Related to this question Where do magnets get the energy to repel? If I have a magnet repelling another, eg one in my hand, the other being pushed along the desk, how do the each of the magnet's ...
2
votes
2answers
289 views

Phase Accumulation of Hankel-waves upon propagation

Hankel functions are solutions to the scalar Helmholtz-equation $$\Delta\psi + k_e^2\psi = 0$$ in cylindrical and spherical geometry (with respect to a separated angular dependence). Thus, they are ...
3
votes
1answer
1k views

Moving conductors in magnetic fields: is there electric field or not?

this is my first question on PhysicsSE (I'm already an user of MathSE). I'm a mathematics students trying to understand Faraday's law, that is $$\varepsilon= -\frac{d \Phi_B}{dt}$$ where ...
0
votes
2answers
342 views

Do and can phone signals come inside AC car which is glass-packed

Can phone signals penetrate glass, so can I expect phone signals to come if I am sitting inside a closed AC car. Thanks,
2
votes
1answer
125 views

Effect of a external EM field on a dielectric

If an external EM field (a laser, for example) act on a dielectric (a glass, for example) what will be the effect of this field on the dielectric constant and on the refractive index of the material? ...
1
vote
2answers
386 views

A lightning protection device physics

Here is a description of the principle of the operation of a new lightning device: During a storm the ambient electric field may rise to between 10 to 20 kV/m. As soon as the field exceeds a thresold ...
2
votes
1answer
597 views

What gauge is used in the Lagrangian for a non-relativistic point particle in an electromagnetic potential

For the Lagrangian $$L = \frac{1}{2}mu^2 - q(\phi - \frac{\vec{A}}{c}\cdot \vec{u})$$ of a non-relativistic point particle in an electromagnetic potential, what gauge is used for the electromagnetic ...
12
votes
5answers
858 views

Making symmetry between E and B fields manifest in Lagrangian

Maxwell's equations are nearly symmetric between $E$ and $B$. If we add magnetic monopoles, or of course if we restrict ourselves to the sourceless case, then this symmetry is exact. This is not ...
3
votes
2answers
2k views

Theories that Relate Gravity, Electricity, and Magnetism [duplicate]

There are some people who (without having a stated theory that I know of) insist that Gravity, Electricity, and Magnetism are related. Some point to symmetry in Maxwell's Equations as a potential ...
1
vote
2answers
439 views

Laplace's equation

I have got some mathematical difficulties in the following exercise : Calculate the potential of the polarized sphere along the z-axis. There are no free charges. For this, we need to solve ...
1
vote
3answers
494 views

Electric field at a point being an $n^{th}$ derivative of electric (or magnetic) field at some other point

This is a theoretical question for which i would like to know an answer with an example. I'd like to know if its possible to create a setup where the electric field at a point $P$ is $n^{th}$ ...
3
votes
2answers
291 views

Gravitational wave energy

Electromagnetic energy can be related to it's frequency via $E=h\nu$. Is there a comparable relationship between gravitational wave energy and frequency?
1
vote
1answer
893 views

How radio waves penetrate through buildings?

For example how radio signals of a base transceiver station (BTS) penetrate through buildings?
21
votes
4answers
12k views

Why do electrons occupy the space around nuclei, and not collide with them?

We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the ...
2
votes
2answers
2k views

Why do bar magnets have least attraction in its center?

Why do bar magnets have the least attraction in its center?
2
votes
4answers
2k views

Induced EMF of a spinning metal rod [closed]

Hey everyone, I'm currently taking an Eletricity and Magnetism course and I'm having dificulty answering this problem. I've gone to my tutor, but sadly, he hasn't taken E+M for a while now and ...
6
votes
2answers
1k views

Lots of little questions about radiation of LC circuits

I'm trying to get a more intuitive understanding of resonant inductive coupling. It's supposed be a more efficient way to transfer electrical energy wirelessly, because the coils are only coupled by ...
1
vote
2answers
268 views

What effect would liquid air have on a resonant coil?

This description of Tesla's "magnifying transmitter", which supposedly used electrical resonance to transmit energy (similar to resonant inductive coupling?) states that the coils (or at least part of ...
7
votes
2answers
376 views

Radiation Resistance

When a charge is accelerated, it radiates and loses kinetic energy. This can be modeled by having another force act on the charge, which is proportional to the derivative of the acceleration. So if ...
0
votes
2answers
995 views

Can quantum communication really replace electromagnetic waves for telecommunication medium in future?

Currently I am planning to get masters degree. So I am thinking about a subject in which I have to get masters degree. Following are my questions to leading physicists.. Which technology is the ...
3
votes
4answers
1k views

Energy conservation in Electrodynamics

Let us suppose that we have a known electromagnetic wave-train of finite size propagating in a certain direction. There is a probe charge on its way. This EMW is an external field for the charge. The ...
2
votes
2answers
1k views

How to estimate inductive coupling between distant air coils

I have two air coils (assume they are simple, circular wire loops). They both have diameter d. There is a distance D between their centres. D is much greater than d (more than 10x greater) Both ...
2
votes
2answers
236 views

Need some help interpreting a formula inspired from Coulomb's law

It has been more than a decade since I did all vector related math and physics so pardon me if my question does not make sense. I am reading some article that says it was inspired from Coulomb's law ...
4
votes
1answer
675 views

How can I model buckyballs sticking together? (Tiny spherical magnets)

Buckyballs are a desktoy that consist of 216 tiny spherical magnets. You can makes all kinds of interesting shapes and structures out of them (do a Google search). I want to model them in a physics ...
4
votes
1answer
776 views

What is the direction of the induced E field from a changing uniform magnetic field?

If a stationary charge is placed in a changing uniform magnetic field to measure the induced E field at some point, what would be the direction of E? I think E must equal zero normal to B to maintain ...
7
votes
4answers
2k views

Measuring the spin of a single electron

Is it possible to measure the spin of a single electron? What papers have been published on answering this question? Would the measurement require a super sensitive SQUID, Superconductive Quantum ...
1
vote
4answers
478 views

Are electromagnetic “plane” waves measurable or just a virtual concept?

I find plane waves are uncompatible with light cone. Perhaps plane waves are "virtual" and can never be measured in that case, shouldn't we call plane waves as "virtual plane waves"? (other option ...
3
votes
0answers
364 views

I lost a factor of two in the electromagnetic field tensor

I apologize for this simple question, but I lost a factor of 2 and can't find it anymore, so now I'm looking on the internet, perhaps one of you has some information about its whereabouts. :-) ...
6
votes
3answers
9k views

Do magnets lose their magnetism?

I recently bought some buckyballs, considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used ...
6
votes
4answers
2k views

How do electrons “know” to share their voltage between two resistors?

My physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people ...
-1
votes
1answer
378 views

What direction does the force vector point in regards to Earth's E and B fields?

In regards to the right hand rule, given Earth's electric and magnetic field, in which "direction" would a particle go?
5
votes
1answer
205 views

Is it true that the angular momentum of electromagnetic waves in an anisotropic medium is an integral of motion?

Extending my previous question Angular moment and EM wave, does it make sense to talk about the angular momentum of electromagnetic waves in an anisotropic medium? It is not obvious that the angular ...
0
votes
3answers
2k views

Direction of Magnetic force from a current running through a coil of wire

What is the direction is the magnetic force vectors pointing from a coil of wire that has current running through it? ...
8
votes
5answers
610 views

How would I go about detecting monopoles?

A question needed for a "solid" sci-fi author: How to detect a strong magnetic monopole? (yes, I know no such thing is to be found on Earth). Think of basic construction details, principles of ...
7
votes
1answer
359 views

Magnetic susceptibility in 1/eV

In this paper the authors refer to transverse susceptibility $\chi_{ \perp}$ [meV $^{−1}$] I was taught that the magnetic susceptibility is dimensionless. How do I get $\chi$ in the above ...
4
votes
3answers
1k views

Cancel the Earth's magnetic field

Is there any reason why Earth's magnetic poles are so close to its axis of rotation, or is it a coincidence? Why does the Earth have a somewhat uniform magnetic field with two poles? If you take a ...
11
votes
1answer
3k views

If a credit card won't read when swiped, does wrapping it in plastic actually help and if so, why?

I've on occasion seen when a cashier has trouble getting a credit card to read, will wrap it in a thin plastic grocery bag, and try swiping it again. Much to my surprise, it seemed to work. Since the ...