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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Electric flux boundary condition

I dont' get why following equations hold isn't equation (3-121b) should be $D_{2n} - D_{1n} = \rho_s$ instead? Since $D_{2n}$ is going outward of the gaussian surface whereas $D_{1n}$ is ...
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27 views

Do gravitational waves interact with the Earth's magnetic field?

Do gravitational waves cause a minor vibration of the Earth's magnetic field, and therefore a minor (if undetectable) electrical inductance?
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1answer
27 views

Plane waves intensity

Our professor said that a plane wave has the same intensity in the plane perpendicular to it's propagation. I can't really make sense of how that is possible. I mean, shouldn't the intensity decrease ...
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24 views

Does an electromagnet use more energy when it is repelling another magnet?

Kind of a strange question. Is the amount of energy used to power an electromagnet directly proportional to the amount of work an electromagnet does? That is, if I were to power an electromagnet ...
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14 views

induction of voltage from power lines to telephone lines

A pair of isolated parallel power lines of 1 cm radius with a separation of 90 cm have a voltage difference of 440 V. These power lines are 60 cm above a pair of telephone lines. The telephone lines ...
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9 views

Superconductive contour

We have a superconductive contour in the shape of circle with radius $a$ . Inductance of contour is $L$, when the contour is out of magnetic field, there's no current in it. What's the current in the ...
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1answer
29 views

Please help me with this doubt from rotational dynamics

Torque to a magnetic field on a current carrying loop is same with respect to any point in space,is the same true for all force couples acting on any body?
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1answer
14 views

Electric field in a cavity of a conductor

I have a spherical conductor with a cavity. A point charge +q is placed in the cavity. Now, on the outside of the sphere, I bring a charge of -q close to the sphere. I understand that the amount of ...
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3answers
65 views

According to Ohm's Law, shouldn't there be a zero electric potential within a capacitor since the current is 0?

If V = I*R, then how does a capacitor store electric potential? The current across a capacitor is 0.
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10 views

Electromagnetic Induction, specifically induced voltage

Why is it that if a conductor 'cuts through' (what does this mean?) a magnetic field that a potential difference is produced? I read this recently in a textbook...
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1answer
63 views

Is Lorentz Invariance necessary for Maxwell Equations?

An example shows that Maxwell Equations do not need Galilean invariance, therefore Lorentz Invariance is not needed for Maxwell Equations. The example: In a train moving at a constant speed relative ...
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19 views

Electromagnetic field tensor [on hold]

How will we derive the component of electromagnetic field tensor by using the electromagnetic field tensor formula; what is the procedure? Can anyone tell me about how I would derive $F_{00}, ...
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4answers
115 views

How do they find the energy of a photon?

Is the actual energy of a photon ever measured? How is it done? I read that a photon is usually identified by diffraction, that means its wavelength is measured, is that right? In this way we ...
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2answers
34 views

How can space strech a wave?

Because of the expanding of the universe a wave from a far galaxy or star can be streched to more red. But how is space doing that? There must be a kind of 'entanglement' between the wave and space. ...
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1answer
19 views

Is the magnetic dipole moment in charged particles the more survivable property than the electric charge?

After asking about Which of the properties of particles are intrinsic properties and why? it was commented "Charge, spin, lepton number, baryon number definitely. Mass maybe." and "is magnetic dipole ...
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0answers
34 views

Electric Filed on a point on a sphere [on hold]

I really want to understand the concept of those problems. Thanks.
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1answer
22 views

Zero or non zero electrical potential energy of the system

Say you have this scenario: and you wanted to find the electric potential energy of the +q charge Now if you were to find the potential energy of +Q and +q system and add that to the potential ...
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0answers
15 views

Why oscillating charges produce magnetic field? [duplicate]

Electron is a charged particle. As far as I know, an electron has an electric field when it is at rest. But when it starts "moving", it creates a magnetic field. How does that happen? How does the ...
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2answers
41 views

Why can only moving metals (aluminium) reflects a magnetic field of a magnet?

A maglev train is riding because the magnets in the train are reflecting their magnetic field on the aluminium rail, so it is lifted up. Also when you rotate a aluminium plate and you hold a magnet ...
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1answer
16 views

calculation od stacked plate capacitor capacitance [on hold]

how we calculate the capacitance of a stacked plate capacitor ? is it the summation of the capacitance of each capacitor $Ci$ ?
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28 views

Electric Field From a point P

A rod of length $L$ and total charge $Q$ creates an electric field at a point $P$, $x$ units away. We need the electric field at this point. I am working on a physics problem for homework and the set ...
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0answers
9 views

Conformal transformation for a vertical strip at constant potential

Say I've got a vertical strip in the $xz$-plane running from $x=0$ to $x=a$ held at a constant potential $V_0.$ The whole of the $yz$-plane is fixed at zero potential. Now I want to find the potential ...
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1answer
30 views

Open Source Particle Tracing Software

I am fairly new to this forum. I am designing an ionospheric plasma testing environment in a thermal vacuum chamber and to do so I require some form of multi-physics package for simulations .. such as ...
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2answers
84 views

How does magnetism work? (Not asking what magnetism does)

To clarify, if I asked "how does electricity work" I would want "electrons flow from a negatively charged area to a positively charged area", not "it powers electronics like phones" as an answer. The ...
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1answer
49 views
+50

Relating Poyntings theorem to Lenz and Faraday's law?

In system's similar to a motor, where the armature begins to accelerate simultaneously there is induced $-\epsilon$ to reduce the applied current(hence the applied power $P(t)$ is also reduced), or ...
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1answer
31 views

Need help to prove the following equation [on hold]

I am able to show the equation at (2) but I am not sure how to show the equation at (3). Any help is greatly appreciated
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0answers
19 views

What causes that the outer electrons of iron have the same spin and creates a dipool?

Iron has the capability of magnetism. The cause of that is that the spins of electrons in the outer shell are the same so they pushes each other away because of Pauli exclusion principle so they are ...
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0answers
30 views

Can the permittivity tensor always be diagonalized?

For an anisotropic medium, permittivity is a symmetric tensor, with elements as $\epsilon_{ij}$ How can one be sure that it is diagonalizable, if some elements, say $\epsilon_{xy}$ and ...
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0answers
13 views

Finding the value of E at a point in a 3D field with 2 separate point charges [on hold]

Having some trouble with this question: A charge 30 nC is situated at the point (x, y, z) = (0, 2, 0) and a charge of –30 nC at the point (0, -2, 0) m. Find E at the points: (a) A = (4, 2, 4) m
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47 views

Kinetic to Electric Energy

Not the best with understanding the formulas involved with the calculations but here is the gist: I want to use Faradays law to convert the kinetic energy from actions such as shaking to produce ...
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0answers
55 views
-2
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0answers
33 views

Reducing a vector calculus relation [on hold]

Someone can help me? I want to reduce this. $$ (\nabla \times \mathbf{B}) \times \mathbf{B} + (\nabla \times \mathbf{B}) $$ Thanks
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0answers
34 views

Free energy in magnetic materials [on hold]

The phenomenological description of magnetoelectrics and multiferroics is based on the series expansion of the free energy is powers of the magnetic and electric fields. WHY IS IT EXPRESSED IN TERMS ...
3
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0answers
36 views

In what circumstances, can exchange interaction acquire temperature dependence?

Heisenberg exchange interaction (sometimes called as magnetic stiffness?), originating from the Coulomb interaction and the Fermion statistics, is widely used in theories of magnetism. Conventionally, ...
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0answers
25 views

How can a moving point charge “update” its fields without emitting an e-m wave?

If an observer brutally moves a point charge from position A to position B, the electric field produced by the point charge at a given point P changes. Furthermore, a delay is observed before this ...
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0answers
18 views

how would an iron encapsulated electromagnet work?

I have been searching for this for a while now, but, a normal electromagnet works with(example) an iron cylinder and a copper coil around it, but would it work the same if you were to encapsulate it ...
3
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1answer
39 views

How does parallel plate lose energy when deflecting charged particles

Say you have a parallel plate setup, each plate is charged with ±Q of charge, and is then disconnected from the power source and is insulated from the environment. There is no way the plates can be ...
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1answer
23 views

Equation relating voltage and minimum rpm needed for generating 1V using a magnet around copper wire

I was wondering if there is any equation or law or something that relates the minimum rpm needed when a magnet spins around a copper wire to generate 1 volt? In other words, how fast does the magnet ...
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0answers
22 views

Electromagnetism(CLOCK RULE)

Can anybody explain why the clock rule has been designed the way it is? I mean , why is it that the polarity is North pole, if current flows in the anticlockwise sense as viewed from above and ...
2
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1answer
295 views

Proof of Ampère's law from the Biot-Savart law for tridimensional current distributions

Let us assume the validity of the Biot-Savart law for a tridimensional distribution of current:$$\mathbf{B}(\mathbf{x})=\frac{\mu_0}{4\pi}\int_V ...
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2answers
54 views

What does it mean to be unique in terms of vector potentials?

I was in an electromagnetism lecture, where we were looking at the magnetostatic Maxwell’s equations: $$\begin{align} \nabla\cdot\mathbf{B} &= 0 \\ \nabla\times\mathbf{B} &= \mu_0\mathbf{J} ...
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2answers
37 views

Ohm's law experiment

I was going through my physics laboratory manual. In the Ohm's Law Experiment, the book states a few precautions without any reasoning. 1.The wire whose resistance has to be determined should ...
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3answers
42 views

Helical motion of charged particle in external magnetic field

When an electron moves in uniform external magnetic field, with velocity not perpendicular, I understand that the magnitude of force is only due to the perpendicular component of velocity and is ...
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2answers
51 views

How does a point charge interact with a Gaussian surface?

A spherical Gaussian surface encloses a point charge $q$. The point charge is moved to to a point away from the center of the sphere. Does the electric field at a point on the surface change? ...
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1answer
28 views

Magnetic field of a current carrying wire reduce/increase exterior magnetic field?

If we place a wire within a uniform exterior magnetic field ($B_x$) that's perpendicular to it's length, and allowed current to flow withing the that conductive medium, there is another magnetic field ...
1
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2answers
28 views

Why is the electric potential of a point from a point charge of +Q positive?

According to the formula, $$V = - \int \vec E \cdot d\vec r.$$ The electric potential of a point charge is $\frac{KQ}R$? However, when I perform the integration, my answer is $-\frac{KQ}R$. Since ...
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1answer
36 views

Energy of electromagnetic wave

Its given here that energy density of an electromagnetic wave is $$\vec S=\frac{1}{\mu}(\vec E\times\vec B)$$ How is the above expression derived? And when did energy become a vector? I though work ...
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1answer
77 views

Light is/produces a electromagnetic wave, but is the opposite also true?

A similar question has been asked, and to some extent the answer is: you need an antenna with $L \approx 200nm$. But it's not entirely clear to me if this is completely hypothetical, as "Marek" also ...
2
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1answer
61 views

Which of the properties of particles are intrinsic properties and why? [on hold]

For macroscopic objects it's clear that - once observed - the observed property does exist for a while, even if we are no longer observing it. That has to do with the complexity and stability of such ...
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3answers
33 views

What is the electric field exactly on the surface of a conducting sphere?

Within the sphere, the electric field is 0, but is the electric field still 0 exactly on the surface?