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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Are Q1 and Q2 attracted or repelled to the sphere shown in the figure below?

Can you tell from the image below if Q1 and Q2 are attracted or repelled. Will Q2 only be attracted to the sphere if Q2 is enough bigger than Q1? Will the positive charge inside the shell attract ...
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2answers
850 views

Apparent violation of Newton's 3rd law and the conservation of angular momentum for a pair of charged particles interacting magnetically

Consider a system of the two identical point positive charges situated in the space (isolated from influence of any other external fields) as shown in the figure.Particle1 is at (a,a,0) and Particle2 ...
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16 views

Finding the magnetic field [on hold]

A mechanical pendulum is made of a metal rod, one end of which is attached to a string. The mass of the rod is $m$ and the string length is $l$. The oscillation period of the thus obtained pendulum ...
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1answer
318 views

Question about superconductivity

A long cylinder of radius $R$ is made from two different material. Its radius $r<r_0$ $(r_0<R)$ part is a material with superconducting transition temperature $T_1$, and its $r_0<r<R$ ...
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8 views

from control torque to magnetic moment

I am designing a system which generates a magnetic field to make itself move in space (a cubesat with magnetorquers). This magnetic field is known as the magnetic control torque, i.e. it will torque ...
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1answer
18 views

How can electric field accelerate fog dissipation?

I should emphasize that I view the problem as a 'research' rather than a 'textbook' level. However, as I am almost unfamiliar with the subject it may be that the answer is elementary and well-known. ...
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0answers
8 views

Atomic flux on the surface?

I have a surface which is made up of two triangles of unequal areas. I impinge a single atom on the surface at a certain angle at a certain time interval. As flux is atoms/unit area/unit time. In ...
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1answer
9 views

Magnetic field size from electric field [on hold]

An electric charge oscillates about the origin along the y axis. A distant observer is located at a point on the +z axis. You observe the wave from a given location and find that at a given ...
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11 views

How can I tell apart the composition of my soft ferrites

I have an assorted bunch of soft ferrites. I need to know which ones are MnZn and which ones are NiZn, so I can sort them for usage at different frequencies.
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1answer
873 views

Local explanation of the Aharonov-Bohm effect in terms of force fields

Here is an interesting paper for the Physics SE community: On the role of potentials in the Aharonov-Bohm effect. Lev Vaidman. Phys. Rev. A 86 no. 4, 040101 (R) (2012). arXiv:1110.6169 ...
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3answers
143 views

What is supposition of equilibrium? How do Rayleigh, Jean know the electromagnetic wave in equilibrium behave?

In a cavity of dimension L, the wave must give zero amplitude at the wall, means wave equation has zero amplitude. Why? Answer from hyperphysics "since a non-zero value would dissipate energy and ...
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2answers
87 views

Understanding magnetic force on charged particle

if we put any charged motionless or static particle in the constant magnetic field, then why does it don't feel a magnetic force? Mechanism by which electric and magnetic fields interrelate I have ...
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2answers
44 views

Potential difference inside charge distributions

Always when I think about potential difference inside a symmetrical charge distribution, I think of it being equal to zero because it's dependent on the field and I imagine the directions of each of ...
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0answers
20 views

Magnetic field due to long current carrying conductor at a point near its end [duplicate]

How can one show that the magnetic field due to an infinite long current carrying conductor (length a) at a point near its end is given by $$B = \frac{\mu_0I}{4\pi a}$$ using Ampere's Circuital ...
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1answer
33 views

Net force between two Electromagnets considering Back EMF

First this Q might be trivial thus apologies. Consider two bar electromagnets that can simulate bar magnets M1 and M2, placed end to end at distance D apart (North Pole of M1 facing South Pole of ...
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1answer
57 views

What are the proposed theoretical explanations for the EmDrive?

The EmDrive is a proposed propulsion mechanism for spacecraft in which some form of microwave device provides the propulsion. The consensus from the physics community, including many voices on this ...
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4answers
7k views

Displacement current - how to think of it

What is a good way to think of the displacement current? Maxwell imagined it as being movements in the aether, small changed of electric field producing magnetic field. I don't even understand that ...
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2answers
213 views

Faraday's law and “infinite induction”

I may have confused after thinking too much about Faraday's law. If an emf is induced in a circuit due to some changing magnetic field, the induced current will be in a direction such that the ...
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1answer
141 views

How does back-emf oppose the input-current?

A circuit, has current $A$ flowing at a certain $V$. When there is a change in magnetic-flux, based on Faraday's law of induction & Lenz's law, we know that there is change in Potential ...
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1answer
139 views

Force of a solenoid on a ferromagnetic material

As I was trying to find an answer to another problem, I was informed that the equation I was using would not work. The equation I was using was $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ If this ...
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0answers
21 views

Why is emf 0 for coil rotating in field?

Say you have a coil (that can carry a current) rotating in the field between two magnets. When the area of the coil is perpendicular to the field lines the emf induced in the coil is 0, why is this?
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2answers
2k views

Proving Ampere's Circuital Law

How to prove Ampere's Circuital Law in case of any conductor. My text gives the proof of only the special case when the conductor is long and straight. I am trying to prove it, but haven't been ...
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1answer
58 views

What is the electric field inside a hollow sphere?

If you have a conducting hollow sphere with a uniform charge on its surface, then will the electric field at every point inside the shell be 0. The reason the electric field is 0 at the center is ...
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2answers
586 views

Neither Biot-savart nor Ampere Law can solve this problem?

I'm confused about the use of the Ampere's Law and the Biot-Savart Law due the inconvenience of each law. I want to calculate the magnetic field due to current carrying a circular loop over itself, ...
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1answer
121 views

Dielectric boundary

I am trying to determine why electric field may be confined to a certain region if there is a large difference in the permitivity for example if electric field flows through water and then reaches a ...
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1answer
39 views

What is the acceleration of a charged particle in uniform electric field [on hold]

I would guess its $kC/r^2$, just like the in the context of gravitation, as one arrives at the acceleration due to gravity $g = GM/r^2$; but I am not sure.
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2answers
633 views

How do magnets work?

I've read a classbook on the field theory (including EM): it perfectly describes quantitive patterns in EM-theory, but I have no luck understanding how and why it works. I mean, magnetic substances ...
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0answers
24 views

Phase added on reflection at a beam splitter?

If we have light of a particular phase that is indecent on a beam splitter, I assume the transmitted beam undergo's no phase change. But I thought that the reflected beam would undergo a phase change ...
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0answers
11 views

What subtopics should I read in order to understand practical electromagnetism? [on hold]

I apologize if this question might be not exactly on-topic here. But it seems related enough, and I found no better place to ask. I'm a student that is fairly behind in his course. I have already ...
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1answer
93 views

Superconducting electromagnets?

Is it true that superconducting electromagnets don't need any power? So... energy to created a magnetic field via a superconductor would be zero? Since resistance is zero, does that also mean that ...
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0answers
11 views

Density of polarisation charge is zero always for linear isotropic homogeneous dielectrics?

It seems to me that the volumetric density of polarisation charge in a linear homogeneous isotropic dielectric in an external field is always zero, but I find this rather surprising. Consider such ...
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0answers
19 views

About the non-physicallity of the scalar derivatives of potentials in Lorenz qauge and longitudinal EM waves [on hold]

First, I'm quoting from a 13 page article: "Within the framework of Classical Electrodynamics (CED) it is common practice to choose freely an arbitrary gauge condition with respect to a gauge ...
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0answers
9 views

Flux due to a charge placed just outside the vertex of a cube [duplicate]

There was a solved example in my book on Gauss's Law. The question says that there is a charge q placed at a distance d outside one of the vertices of a cube such that d tends to 0.My objective is to ...
2
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1answer
31 views

Is it possible for two polarizable bodies to induce dipoles in each other in the absence of an external electric field?

If there exist two initially neutral bodies (say atoms) some distance apart, with no external electric field applied, can they induce dipoles within each other?
2
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1answer
26 views

What about a material makes it diamagnetic

For a material to be magnetic, all the magnetic atoms (atoms with half filled electron shells) need to be aligned, but what about a material gives it the property of diamagnetism?
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0answers
30 views

How do I calculate the energy flux for this toroid?

My question is how do i calculate the total energy flux through the walls of the torus in this situation? The Poynting flux is given by $\vec{N} = \frac{1}{\mu} ( \vec{E} \times \vec{B})$ but the ...
5
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1answer
49 views

How long does it take a magnet to lose its magnetization? [duplicate]

As we all know, a magnet has some magnetization that lets it attract other ferromagnetic materials but I was wondering how long it takes to lose this magnetization? Is it even possible or not?
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23 views
2
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29 views

Current Density Boundary Conditions and its Implications

According to Ohm's Law, one can say $ \overline{J} =\sigma \overline{E} $ if the field is in a conductor, and $ \overline{J} =0 $ if it's in empty space. Now if we take the surface of a conductor and ...
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1answer
44 views

Why is the Meissner effect not used for levitation in MagLev trains?

The Meissner effect does not seem to be used as primary source of levitation in MagLev trains, instead, electromagnetic and electrodynamic syspension are mainly used. Why is this? Could it be that the ...
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0answers
19 views

Are the EM waves that result from each of these processes distinguishable? Phase of light upon emission

In case 1, you have a single source of light that you pass through a diagonally oriented linear polarizer and then a half waveplate, such that the horizontal and vertical components become $\pi$ out ...
2
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1answer
51 views

How does radiation degrade mechanical parts and electronic devices?

I'm running out of places to look (lots of Googling, SE, [articles and books are too specific and never give a good overview]), and yet I am still unsure about how exactly radiation can degrade ...
8
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1answer
3k views

Can microwaves affect WiFi?

I listen to the radio via my iPad with wifi. When I switch the microwave oven on, the radio cuts out. When the microwave oven is finished, the radio comes back on. (This is 100% reproducible!) So - ...
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0answers
15 views

Can a magnet lose its strength over time? Especially when repulsive magnets are around? [duplicate]

I was thinking of hanging delicate art glass pieces separated by opposing magnets on walls simply using the power of magnets. I was wondering will the opposite poles have any effect on the strength of ...
2
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3answers
213 views

About field gradient

I read the term field gradient in most of the article about magnetic field. I search it online but most of the explanation is about the math. I wonder in physics, what the gradient field really mean? ...
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0answers
21 views

Is it possible to focus an electromagnetic field such as an aura into a stream of pure energy? [on hold]

Is it possible to focus an electromagnetic field such as an aura into a stream of pure energy? http://www.biofieldglobal.org/what-is-human-aura.html
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2answers
59 views

Proof that work is the same whaever the path of approach for two charges

I have a quick question on a figure that outlines a proof. There is a stationary charge $q_1$ and is kept fixed. $q_2$ is moved to the same position along two different paths at a fixed distance ...
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1answer
282 views

Force on a coil inside of a voice coil

as a homework exercise we were given the following question: Given the following voice coil: With depth = 20 mm Permanent magnets with B = 1.23 T, Ur = 1.1 The coils has 20 turns, I = 1 Ampere. a) ...
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2answers
56 views

Does a moving charge have additional (magnetic) energy

My understanding so far: A moving charge produces a magnetic field, B, in an analogous way to a current produces one. A magnetic field has an energy density which is proportional to B squared. My ...