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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Understanding the relationship between electric energy and force

I'm trying to do the following problem: One of the three types of radioactive decay is "β decay", during which protons decay into neutrons or vice­versa, emitting either electrons (β­) or positrons ...
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16 views

What should the magnitude of the induced voltage on the 2nd loop of a transformer be?

so I'm trying to understand transformers and am reading this site: http://www.allaboutcircuits.com/vol_2/chpt_9/1.html I am a little confused about how to reason about the voltages involved in a ...
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17 views

How could the effective electric dipole interaction be derived

In some papers (e.g. Bernreuther equation (1.4) http://inspirehep.net/record/296679 ) you can find the electic dipole interaction defined as $$L_I=-\frac i2 d_f\bar\psi\sigma_{\mu\nu}\gamma_5\psi ...
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18 views

Work functions of ceramics

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, ...
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2answers
29 views

Why can't I connection the anode of a battery to the cathode of an other battery and get a current flowing?

If I touch the anode of a battery or connect the anode the the cathode of an other battery, none (or rather: a very small current) flows between those two. If I instead connect the connect the anode ...
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2answers
42 views

How can a magnetic field accelerate particles if it cannot do work?

A varying magnetic field can accelerate charge particles, but it is said that a magnetic field can't do any work so it should be able to speed up charged particles, right? How is this apparent ...
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1answer
57 views

I need help with divergence and gradient? [on hold]

$$A_z = \mu{\frac{e^{-jBr}}{4\pi r}}∫I(z')e^{jBz'\cos\theta}dz'$$ Midway into my question, I want to compute: $$-j\left( \frac{\nabla(\nabla\cdot A) }{w\mu\varepsilon} \right).$$ Symbols like $ w, ...
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1answer
15 views

potential inside a cylindrical shell in terms of the surface potential?

Given a potential distribution $V(\phi)$ at the surface of an infinite cylindrical shell, is there an easy way to derive the potential inside the cylinder. No charges or currents anywhere.
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1answer
19 views

Negative power measurement of transformer short-circuit test. What happened?

I have a dissectible transformer, made up of two 120-turn coils. I connect a function generator to the primary side, set the AC voltage to be constantly 10V, and short circuit the secondary side. And ...
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12 views

electron trajectory in Bfield with energy kick at midpoint

So I wanted to get some second opinions on this situation I have thinking about.Lets say an electron enters, normally, a section of bfield that is perpendicular to its motion such that the electron ...
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2answers
61 views

Derivation of Faraday's law using Lorentz force?

For a stationary loop of wire with a time varying magnetic field $\vec{B}(t)$ through it. Is it possible to derive Faraday's law, using only the Lorentz force $$\vec{F}=q \vec v\times \vec B \tag ...
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23 views

can we reuse the motion of a dc motor to power an ac generator

My question is ,when we make a simple dc motor, cant we connect another circuit to the rotating coil and make another circuit for an ac generator
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1answer
98 views

Does magnetic monopole violate $U(1)$ gauge symmetry?

Does a magnetic monopole violate $U(1)$ gauge symmetry? In what sense and why? Insofar as I know, there are at least two types of magnetic monopoles. One is the Dirac monopole while the other is the ...
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3answers
65 views

Induction and electromagnetic fields

I've got a few questions on induction and electromagnetic fields. My current understanding of induction and electromagnetic fields is that, when electricity/current flows through a wire, it creates an ...
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31 views

Difference between Reed Relay, Reed Switch and Just a Relay? [on hold]

Whats the Difference between a Reed Relay and and Just a Relay, and How does it work.
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3answers
85 views

The propagation of electric field

In case of a charged particle which is travelling at a uniform velocity, the electric field due to it at a given point doesn't change instantaneously . The reason for this delay in change of electric ...
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1answer
17 views
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1answer
40 views

Force acting on a polar molecule

What kind of force does act on a polar molecule? I mean, there must be a force that is acting on the molecule to keep the negative and positive centre away ( like in H2O). Why the positive and ...
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0answers
26 views

problem on electromagnetic induction and newtonian physics

Please imagine a solenoidal toroid (i.e. a donut shaped inductor) powered by an AC voltage source. It creates a changing magnetic field which is confined to the interior of the toroid (i.e. within the ...
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1answer
24 views

Electromagnetism and static electricity

What is the difference between electromagnetism and static electricity? Also electromagnetic waves are mediated by photons , what mediates static electricity?
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20 views

Earth's magnetic field and the equator

Suppose earth is like a bar magnet with the poles acting as N and S. If a charged particle from outer space heads towards the equator, why does it get travel around the field instead of the magnetic ...
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2answers
73 views

Why does light travel as waves? [duplicate]

Why does light travel as waves instead of say just a straight line? What are the forces that make a light photon travel in a wavelike pattern?
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2answers
121 views

Are electron fields and photon fields part of the same field in QED?

I know in classical field theory we have the electromagnetic field. And Maxwell's equations show how electromagnetic radiation can propagate through empty space. I also have been reading about QED ...
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1answer
48 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 ...
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2answers
38 views

Predicting Polarity of capacitor in the given diagram

I have to determine the polarity of the Capacitor in the given diagram. I Approached the problem as follows: When Magnet 1 moves with its North pole towards the coil, emf is induced in the coil as ...
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11 views

ratio between conduction current and displacement current

First, recall that Maxwell displacement current for a plane wave is $$ \vec j_D = \epsilon \partial_t \vec E = \epsilon \partial_t (\vec E_o cos(\vec k \cdot \vec r - \omega t)) = \epsilon \omega ...
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0answers
21 views

Time-dependent electric and magnetic field between two point charges

I would like to get expressions for the time-dependent electric and magnetic fields in the region around two moving point particles. I can't see how this is possible. Clearly you can't use Gauss' Law ...
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36 views

Space between Gas molecules

We know gas molecules are in random motion. There is obviously space between gas molecules. But I doubt that it is not vacuum,because if it was vacuum then how would the propagation of sound through ...
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42 views

What are some open problems in classical electrodynamics? [duplicate]

I am about to finish reading 'Introduction to Electrodynamics' by David Griffiths. Throughout the textbook, Griffiths makes frequent references to current literature (mostly articles from American ...
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1answer
49 views

Current distribution on a dipole antenna

It is known that the current distribution on a thin dipole antenna is always sinusoidal: http://www.antenna-theory.com/antennas/dipole.php How can I prove this?
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2answers
63 views

How is the electromagnetic Lagrangian derived?

I've been studying from the book called "path integral formulation" by Feynman and Hibbs. In chapter 4, problem 4.2, they refer to the electromagnetic Lagrangian as: $$ L=\frac{1}{2} m \dot{x}^2+ ...
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27 views

If we put diamagnetic material under strong electromagnet.Would the opposing magnetic fields strong enough to attract ferromagnetic materials?

Suppose we put a diamagnetic material (such as Bismuth or Pyrolytic Carbon) under a strong magnet (see image below). It would create opposing magnetic fields. Would the opposing magnetic field be ...
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0answers
32 views

Whether Newton's 1st law is true to solitary electron or proton? [duplicate]

Newton's first law: "every body maintains a state of rest or uniform motion as long as the action of external forces will not force him to change this state." Whether this law is true to solitary ...
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2answers
387 views

Why doesn't my mobile phone pick up the electro-magnetic wave emitted by my water heater?

I admit my knowledge of physics is very little, but I did study topics on EM and stuff in school. I was reading about computer networks and I read about antennas and how they are just wires or strips ...
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11 views

Why is the force acting on a coil unchanging (motor effect?) [on hold]

could some please explain why the upwards force acting on a coil remains constant, and whether back emf has an effect of the magnitude of the force? Thanks NOTE: this is not homework, I just want to ...
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13 views

Calculating the strength of an electromagnet with a closed magnetic circuit core

I am interested in calculating the magnetic field strength produced by an electromagnet with a core shaped like an O that forms a closed magnetic circuit, shown in the attached image that can also be ...
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14 views

Holding a photolithography mask (EUV litography) with magnets, to minimize deformation on the photomask?

Some background: what is this question about? On 20/11/2014, I visited the ASML Holding in the Netherlands, which is according to them, and according to Wikipedia: the largest supplier in the ...
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1answer
24 views

Accelerating an electron to a high speed

Suppose there are two vertical metal plates. They are separated apart by a small distance. While one is grounded, the other one has a potential of some $V$. Now suppose electrons are produced at the ...
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4answers
75 views

How eddy current brakes function

Take the following example: where a rectangular sheet of metal is entering a constant magnetic field at $v \dfrac{m}{s}$. Due to Faraday's law of induction + Lenz's law, we can state that an eddy ...
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25 views

Understanding magnetism [closed]

How much has been magnetism understood with the present knowledge of Science? of what I read they have discovered the magnetism particles are virtual photons.How do these photons work to attract or ...
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1answer
19 views

Effect of iron rod on an inductor

When a iron rod is inserted in the inductor coil a circuit containing a bulb and an inductor .how is the brightness affected→ 1. When emf source is AC 2. When emf source is DC
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15 views

What is the charge distribution on inner walls of arbitrary cavity of a spherical metallic shell with charge present in it?

Consider a spherical metallic shell with a cavity and a charge $q$ present inside. The field at outside points will be as if charge was placed at the center of the shell.That means the field due to ...
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23 views

Proof Verifying on EM waves generated by an oscilating dipole [closed]

Statement: The electric and the magnetic field due to an oscilating dipole have the same phase "far" away from the source (the dipole itself) Question: Is my proof correct? Proof Let A,B be ...
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9 views

Can this electrcity generated by a superconductor used for other purposes other than levitation? or together for both purposes

i want to ask whether the electricity produced by superconductor can be used up of other purposes other than levitating it, or can it be used for two purposes that are levitation and for eg lighting ...
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15 views

Are some sources of electromagnetic radiation theoretically (or perhaps technically!) more challenging to detect than others?

In a previous question, I learned that in order to detect an object in space, what matters is how much electromagnetic radiation it is giving off, and what sources of EM radiation the sensor can pick ...
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2answers
58 views

Origin of the Lorentz force from the point view of relativity?

I'm a physicist, when I'm working on the quantum spin hall effect, I recollected the high-school knowledge on Lorentz force and try to explain the origin of it, but didn't get it in the first glance. ...
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3answers
84 views

Two mirrors paradox revisited

If I connect a video camera to a screen, so that whatever is seen by my camera appears on the screen, what do I see when I point it towards the screen itself? Is it, in terms of optics, this ...
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1answer
27 views

Given a Magnetic Field vector, what is the Electric Field, charge density, & current density?

I tried searching for this before having to ask, so please forgive me if I missed a previous question similar to mine. This is a Grad class, so I may be unnecessarily too careful in not assuming ...
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1answer
38 views

Fields and the way they should be looked at

When I think about the electrostatic interaction and interaction of charged particles having uniform velocities sometimes I do find it giving rise to a picture of superluminal communication which ...
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20 views

Anyone know of a flow chart or list of common/useful consequences of Maxwell's equations?

I just recently started to appreciate the Maxwell equations. I had never really take the time to study them but I feel like I'm finally more familiar with them. I've noticed that it seems like a lot ...