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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The relation between electric and magnetic potential equation [closed]

Use the principle of duality to derive: $$\textbf{A} = \frac{\mu e^{-j\beta r}}{4\pi r}\int\int_S\textbf{J}_s\, e^{j\beta\, \hat{\textbf{r}}.\textbf{r}'}dS'$$ from this $$\textbf{F} = ...
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2answers
55 views

Does magnetic poles exist for a magnetic field generated by straight current carrying conductor?

I read that a straight current carrying conductor generates magnetic field around it in form of concentric circles. If so, where would be the poles of this field.
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1answer
45 views

Would it be efficient to run a solar panel with laser?

Would it be efficient to run a solar panel with laser? I know this question is unsual as we are using electricity powered laser to run a solar panel. Actually i am paricipating in the Google Science ...
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0answers
89 views

Why is gravity so weak? [duplicate]

How does physics explain the enormous disparity between the gravitational scale and the typical mass scale of the elementary particles? In other words, why is gravity so much weaker than the other ...
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2answers
52 views

Why are magnets made in only a few shapes?

Additionally, why are all magnets solid? For example, why can't a magnet be made in the shape of a PVC pipe (very long tube)?
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43 views

Question about DC & AC Generators

Main question: moving a alternating magnetic field past a coil can create AC, if the same pole is moved past repeatedly does this still generate the same amount as the AC version would? or is the ...
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1answer
48 views

How to calculate earth's magnetic field by time period of suspended magnet?

Assuming that torsion of the suspension wire small enough to be neglected, how can we derive earth's magnetic field by measuring time period of an oscillating magnet suspended on a string?
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1answer
40 views

Do/May pure electromagnetic waves ( Non dual natured ) exist?

The light as well as all matter 'particles' show dual nature. But my question is if according to the Maxwell equations, Electromagnetic waves are valid events, can they actually exist in pure wave ...
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2answers
44 views

Why doesn't current induced by changes in flux affect the flux, while current induced by a battery does?

Faraday's law states $V=-\frac{\mathrm{d}F}{\mathrm{d}t}$, where $F$ is flux. Since $V=IR$ for passive circuits, $I = V/R = -\frac{1}{R}\frac{\mathrm{d}F}{\mathrm{d}t}.$ But by the Biot-Savart law, ...
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16 views

How does the phase of an alternating current change when flowing through a multi-layered material?

I have questions regarding the properties of the alternating electrical current in the following imaginary experiment: There is an AC (sinusoidal wave with frequency $f = 5\ \mathrm{Hz}$). I would ...
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2answers
94 views

Derivation of Jefimenko's Equation in Jackson's EMT book

I have been trying to understand the derivation of Jefimenko's equation in Jackson on p.246-247 which can be seen in the photographs attached. First of all I did not fully comprehend the ...
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1answer
42 views

Aharonov-Bohm experiment: A possible way to understand potentials?

I'm posting this question as a function of an another question I found here: What is potential energy truly? The answer of WetSavannaAnimal aka Rod Vance. As I understand the hole point is to see ...
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64 views

Flux Linkage Inside of a Conductor

Can someone explain to me why the flux linkage inside of a conductor is dependent on the cross sectional area of the conductor? My book says that d$\lambda$ = $\frac{x^2}{r^2}$$\phi$. Where $\phi$ ...
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36 views

Hydrogen atom Ionization by Magnetic Field [closed]

The source of a magnetic field (it could be a magnetic dipole) is moving at relativistic speed. This magnetic field encounters a hydrogen atom at rest with respect to the source. Will this encounter ...
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1answer
86 views

Radiation pressure (Jackson exercise)

Here's an exercise from Jackson: A plane wave is incident normally on a perfectly absorbing flat screen. From the law of conservation of linear momentum show that the pressure exerted from the ...
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1answer
51 views

Show that a solenoidal field is always a curl of a vector field [closed]

Can someone prove that: $$\nabla \cdot \mathbf{B} = 0 \implies \mathbf{B} = \nabla \times \mathbf{A}~?$$ I know that $$\nabla \cdot (\nabla \times \mathbf{A}) = 0$$ identically. But can one prove ...
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1answer
127 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 ...
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1answer
32 views

An equation for any charge distribution in a constant external electric field. Is it correct?

Is the equation (torque, $\tau = p \times E$) correct for any kind of charge distribution? (E is an external constant electric field.) If so, why? Will somebody prove it to me? I'm only sure of its ...
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0answers
202 views

Was Nikola Tesla right about his ether theory?

There are a lot of articles on the net that mention Nikola Tesla's ether (aether) theories (like this). Was there any truth to this idea of his ? Why was it rejected by the scientific community ? Did ...
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2answers
66 views

Effect of a magnetic field on a current carrying wire

When a magnetic field is applied perpendicular to a current carrying wire, a Lorentz force $$\mathrm{\vec{F}=i(\vec{L}\times\vec{B})}$$ acts on the conducting wire. Of course the applied magnetic ...
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1answer
53 views

Time changing potential gives rise to “force”?

Imagine a charged particle inside a Faraday cage (i.e. charge on outside, zero electric field inside, but non-zero electric potential on the inside). Suppose the charge distributed on the outside of ...
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0answers
12 views

Electrodynamic near fields around black holes

For the standard Schwarzschild black hole, the temperature of Hawking radiation is simply related to the Schwarzschild radius as $kT = \hbar c/(4\pi r_S)$, meaning that the typical wavelength of ...
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40 views

Does the Lorentz force law explain Flemings left hand motor rule and the right hand dynamo rule?

the Lorentz force on a charged particle $F=qv \times B$ can explain Flemings left hand rule (motor rule) and the right hand (dynamo rule) In the left hand rule, the direction of the current gives ...
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1answer
25 views

Poynting vector from 1st term in Lienard-Wiechert field

I start with 1st (non-radiative) term from Lienard-Wiechert fields: $$ \vec{E} = q (1-v^2) \frac{\vec{R_{t'}} - \vec{v}R_{t'}}{(R_{t'} - \vec{v}\vec{R_{t'}})^3} $$ $$ \vec{H} = - q (1-v^2) ...
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4answers
9k views

Why doesn't light, which travels faster than sound, produce a sonic boom?

I know that when an object exceeds the speed of sound ($340$ m/s) a sonic boom is produced. Light which travels at $300,000,000$ m/s, much more than the speed of sound but doesn't produce a sonic ...
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1answer
35 views

Concerning railguns and magnetic fields

I'm part of a group working on a Physics II project based on electromagnetism, and my group decided to create a proof-of-concept railgun, shown here: ...
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1answer
38 views

Physical meaning of the separation constants in Laplace's Equation for Electrostatics

In Electrostatics, if we consider a region without charges the electrostatic potential $V$ obeys Laplace's Equation $\nabla^2 V = 0$. We can tackle this with separation of variables. In cartesian ...
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1answer
19 views

What are the general rules for determine on which two ends of a bar magnetic are its poles located?

I am wondering. Maybe somebody be nice enough to put a explanation that doesn't involve too much math. I did notice that for bar magnets, their poles are not always on the two ends separated by the ...
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0answers
48 views

From Liénard-Wiechert to Feynman potential expression

When studying the potential of an uniformly moving charge in vacuum, Feynman proposes to apply a Lorentz transformation on the Coulomb potential, which reads in the rest frame $ \phi'(\mathbf r',t') ...
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1answer
54 views

Motional emf with rod

We know that $\mathcal{E} = -N \frac{\mathrm{d}\phi}{\mathrm{d}t}$. When we have a rod such as the one on the left moving through a constant magnetic field, how is it the case that the flux is ...
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0answers
12 views

Is there a magnetic force affecting point charges outside of a toroidal coil with sinusoidal current?

To clarify my question a bit more, if we have a toroidal coil with sinusoidal current flowing through wires around the core of the toroid, is there a magnetic force that affects charges outside of the ...
4
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2answers
253 views

Maxwell's equations invariant under all linear transformations?

Maxwell's equations in tensor notation read: \begin{align} \partial_\mu F^{\mu\nu} &= J^\nu \\ \partial_{[\lambda}F_{\mu\nu]} &= 0 \end{align} Consider doing a general coordinate ...
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0answers
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MRI and precession

A lot of explanations of the quantum mechanics of MRI discuss the precession of a proton in an external magnetic field, for example here: http://www.physicscentral.com/explore/action/mri.cfm Doing ...
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2answers
80 views

Why do we feel hot because of sunlight? [closed]

sunlight , light generally , is an electromagnetic wave which turns into heat when it contacts a matter (solid,liquid,etc..) is that right ?
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2answers
60 views

why do electromagnetic waves have no charge?

i would have thought that because the electric and magnetic fields oscillate, the charge could be positive or negative between 0 and 1 inclusive at any one point in time. i cannot see any explanation ...
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24 views

langevin theory of diamagnetism

According to langevin diamagnetic theory when an electron orbiting the nucleus is subjected to an uniform external magnetic field (say perpendicular to plane of orbit) then the angular frequency of ...
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1answer
65 views

Shouldn't the currents be time-continuous here?

My intuition is that the current upon an inductor (say, a solenoid) will always be time-continuous, without "sudden changes". But below is a case that seemingly contradicts this point of view. There ...
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3answers
96 views

What makes waves propagate?

Why do electromagnetic waves propagate? I have searched a lot about EM waves, but I am still unable to understand what is driving them. Could you explain?
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0answers
10 views

Relation between frequency, speed, and coverage range

From http://superuser.com/a/901075/9265 about wireless network: Higher frequency signals degrade over shorter distances, but can carry data more quickly. I wonder what theorem/theory in Physics ...
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1answer
40 views

Question regarding charge and acceleration

From a stationary charge electrostatic fields arise. From a moving charge, magnetostatic fields arise. From an accelerating charge, EM waves arise. So i wonder -- what about a non-constantly ...
2
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1answer
49 views

Special relativity, electromagnetic fields, charge and Q

Is it true, were Coulomb's constant k to be several orders of magnitude smaller, that there would be no (or increasingly negligible) magnetic fields generated by moving charges? The reason being the ...
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1answer
37 views

Current direction and magnetism

So using the right hand rule, I understand current is clockwise. Because I read the magnetic field emerges from the north pole, I thought the answer was a, that the north pole is on the top. But the ...
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3answers
253 views

What does it mean that a magnetic field's flux vanishes through any closed surface?

I'm reading the Britannica guide to Electricity and Magnetism, and I came across the following quote: A fundamental property of a magnetic field is that its flux through any closed surface ...
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4answers
134 views

A current through a wire produces a magnetic field around it. Is the reverse possible?

If somehow a magnetic field around a wire can be made to exist that is identical to the magnetic field produced when a current passes through the wire, will a current be produced in the wire?A thought ...
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2answers
63 views

When does $\mathbf n\times(\nabla V_2-\nabla V_1)=0$ imply $V_1=V_2$

I was reading a paper on electrohydrodynamics which has the following sentence (in my own words): At the interface/boundary, the requirement of continuity of the tangential component of the ...
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1answer
38 views

Neutral $K$ and $B$ mesons decay to 2 photons?

The neutral pion $\pi^0$ decays almost exclusively to 2 photons, $\pi^0 \rightarrow \gamma \gamma$, which got me thinking: Can we have $K^0 \rightarrow \gamma \gamma$ and $B^0 \rightarrow \gamma ...
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2answers
60 views

Is there no electric field inside a conductor?

I came across this statement while studying electric currents and I am confused: "There is no electric field inside a conductor. Hence no current can flow through it". Is there a fallacy in this ...
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13 views

Eddy currents are out of phase with respect to the field generated by a coil?

I have a coil from which a sinusoidal current (low frequency, few kHz) should generate a precise AC magnetic field in the surrounding space. Another coil intercepts this field and the corresponding ...
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27 views

Magnets quantum locking/levitating [duplicate]

How does cooling a magnet allow it to quantum lock/levitate? I have seen it in videos but do not know how it works.
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2answers
49 views

Are magnetic field lines level sets?

I have been learning a bit about level sets. After doing this, I looked at a diagram of magnetic field lines and noticed they don't intersect rather like the lines on closed curve level sets. My ...