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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Current carrying conductor with a loop at a distance [on hold]

In Fig, there are an infinitely long conductive wire and a circle conductive loop C with the radius r and the number of turns n. The distance L between the wire and the loop is much larger than r, ...
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13 views

Why diamagnetic material is not repelled?

When an external magnetic field is applied to a diamagnetic materials, their atomic current loops will tend to align in such a way as to oppose the applied field. Diamagnetism is the residual magnetic ...
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34 views

In Solution of the equation $\Box A_\sigma=0$. I find some mathematical difficulties

The solution of the equation $$\Box A^\mu(x)=0$$ has the form $$A^\mu(x)=\int\frac{d^4k}{(2\pi)^4} e^{ik^\mu x_\mu}A^\mu(k)\delta(k^2).$$ Where we take $A^\mu(k)$ of the form $$A^\mu(k)=\sum ...
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23 views

How to calculate the potential energy of a magnetic dipole (with zero torque)

In the following problem, I would like to know how they arrived at their solution for finding the potential energy of a magnetic dipole (boxed in red). I understand I probably have to use the ...
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1answer
24 views

Explanation of different magnetic field measurements due to frame of reference

If there is an stationary infinitely long wire carrying current I, and we turn on a gaussmeter, it will record a magnetic field B. Since I know the Biot-Savart law, I am satisfied with this ...
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13 views

Electric field/ Gauss´s Law [on hold]

if I want to calculate the electric field, since I have 3 charged densities. The first one is -2 microC/m^2 , the second one is +4 microC/m^2 and the third one is -5 microC/m^2. What would be the ...
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18 views

Magnetic levitation manipulation

Suppose a small crystal or mineral piece with a completely known structure was held by magnetic levitation. Would it be possible to orientate the piece by manipulating the magnetic field so that a ...
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1answer
23 views

Continuity equation for charge and current densities of an accelerated point charge

For a point charge that moves with the trajectory $ \vec r(t)$, we know that it has the singular charge and current densities $$ \rho (\vec x, t) = q \delta^3(\vec x - \vec r(t)) $$ $$ \vec J(\vec x, ...
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1answer
32 views

Do two bodies spinning about the same axis in the opposite direction repel each other?

I recently read about the GEM equations, which look very much like the Maxwell's equations. Does this mean the behavior of mass is like the the behavior of the electric charge? So for example if you ...
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15 views

Is the induced EMF dependent on the conventional or actual flow of electrons?

I have been studying Faraday's Law and Lenz's Law and the flow of current to oppose change in flux linkage. My question is whether the actual flow of electrons to the top of a material makes the EMF ...
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1answer
19 views

Confusion regarding Changing flux

I have a confusion regarding where flux changes and where it is constant. When a flat coil moves between two opposite poles of a magnet, parallel to their faces we say the flux is constant and no ...
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21 views

Is there a method to detect a magnetic field within this range: 100 fT to 1 pT

Is there a method to detect a magnetic field within this range: 100 fT to 1 pT (human brain magnetic field) I know there are SQUID magnetometers currently using in primarily Medical Researches. But ...
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63 views

Paper challenging Einstein - Thoughts and comments? [on hold]

I recently came across this paper and wondered what peoples thoughts were on it. He aims to show 'On the Electrodynamics of Moving Bodies' by Albert Einstein is incorrect in his paper "Experimental ...
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2answers
24 views

How do I choose the right value of $r$ to find where the electric field is zero?

Sorry for the long question. I'm having a difficult time trying to explain my confusion. I have a positive point charge$\ Q_1 =+q$ at the origin and a negative point charge $\ Q_2 = -2q$ at $\ x=2$ ...
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2answers
39 views

Is there any macroscopic experiment that reproduces the results of Stern-Gerlach experiments on electron spin?

In a Stern-Gerlach experiment measuring electron spin, electrons are diverted to one of two areas on a detector, rather than ending up in a continuum between those two areas. I'm wondering if there is ...
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25 views

Physical reality of calculated wavelength from two measurable phenomena slit distance and fringes distance?

I see some difficulties in answering this question (Have we really measured the wavelength of light?) about the measurement of the light's wavelengths with double slit interference. "... we can find ...
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2answers
64 views

Can Ampere's law be applied to 3D loop

Usually in textbooks Ampere's law is just illustrated using 2D loops which forms a plane. Can the law be applied to 3D loops which cannot form a plane surface within the loop? In a 3D loop which ...
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36 views

Amplitude of eliptically polarised light

In elliptically polarized light, can one define something called amplitude of Electric field? If yes, how do we determine it?
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1answer
19 views

Since electron clouds of different atoms repel each other, does that mean that touch is the feeling of electromagnetic repulsion? [duplicate]

Also when we rest our hand on an object does that mean we are effectively levitating because of the repulsion of the electron clouds?
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32 views

How do I convert a specific absorption rate from W/kg to eV/kg/ps [on hold]

Specific Absorption Rate (SAR) is the rate at which electromagnetic energy is absorbed by water, human tissue or any other material. After performing an electromagnetic simulation i got the below ...
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1answer
23 views

Voltmeters and changing magnetic fields

A changing magnetic field pierces the interior of a circuit containing three identical resistors. Two voltmeters are connected to the same points, as shown. V1 reads 1 mV. What does V2 read? ...
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1answer
59 views

Have we really measured the wavelength of light? [duplicate]

Have we practically measured the distances between the variations of electromagnetic radiations in space in nanometers or is it just theoritical because of calculations? Also the one who have marked ...
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23 views

Voltage between conductors in single phase line [on hold]

I am trying to understand capactiance between conductors in a single phase line, but I am stuck, I am following this ...
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26 views

How do I show $e_r$ and its first- and second time derivative?

What does a charge q moving in a circular orbit with a constant velocity (a "rotating charge") and a stationary observer that measures the E field look like? And how do I show $e_r$ and its first- and ...
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1answer
24 views

The magnetic field between two intersecting cylinders [on hold]

Consider a cable of infinite length whose section has the form of two intersecting circles of same radius $a$. The first part is then a cylinder of constant volume current density $J$ along the ...
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1answer
48 views

Why isn't the magnitude of the electric field in a circuit zero?

I've been re-reading my knowledge of circuits and how current flows as well as the surface charge distributions in the steady state, since it's been quite some time and we've just started studying ...
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1answer
20 views

Units for displacement current density

The displacement current density, $$\mu_0 \epsilon_0 \frac{\partial \textbf{E}}{\partial t}$$ has units of (N/A^2) (C^2/Nm^2) N/Cs = Ns^2/(Cm^2) which is not the same for current density: C/sm^2 ...
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30 views

The relation between electric and magnetic potential equation [on hold]

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
43 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
42 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
87 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
50 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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42 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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49 views

Angular momentum of light in classical electrodynamis [closed]

I' reading at this time electrodynamics from Griffith's Introduction to electrodynamics. As i see, to have the conservation laws in field theory we have to consider the fields as carrying energy, ...
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156 views

JEE MAIN 2015 Question. Electromagnetism [closed]

Two coaxial solenoids of different radii carry current I in the same direction. Let F1 be the magnetic force on the inner solenoid due to the outer one and F2 be the magnetic force on the outer ...
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1answer
34 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
36 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
35 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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13 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
80 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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39 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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57 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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28 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
77 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
44 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
98 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
26 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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158 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
53 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 ...