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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3answers
210 views

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

In a cavity of size $L$, 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 violate ...
0
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0answers
12 views

How much damping is there being exerted on a vertically stable magnet moving across a superconductor surface?

I'm thinking of a flat magnet with opposite poles on the wide ends, though perhaps some other arrangement is more stable. Assuming such a magnet is levitating in a completely stable state and is ...
0
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0answers
41 views

Gradient of Greens function

This question is about Jackson's equation (10.75) and (10.77) I don't know the step in between these two equations.I'm not sure what our unit vector $n'$ will be here and how can we take gradient of ...
0
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1answer
50 views

Metal Sphere in a Uniform Electric field

An uncharged metal sphere of radius $R$ is placed in a uniform electric field $\vec{E} = E_0 \, \hat{z}$. The field will push the positive charges to the "northern" surface of the sphere, and the ...
4
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1answer
46 views

What is the QED model about half wave plate?

Surely classical electrodynamics (CED) has a good and well-known answer about the change of light polarization in a HWP (or Quarter wave plate). I tried to find how does this look like from point of ...
1
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0answers
24 views

Can orbital angular momentum of an electron be changed?

In a lab at my university they are working on a project that deals with changing the "net magnetization" of a material by "flipping" the spins on some electrons. Is orbital angular momentum not ...
1
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1answer
35 views

Why is diamagnetism more common than paramagnetism or ferromagnetism?

Why are there more diamagnetic substances in nature than there are paramagnetic or ferromagnetic substances?
1
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1answer
20 views

Mie theory: Interpretation in terms of intensity

I'm trying to understand Mie theory. For this I'm reading the book "Absorption and Scattering of Light by Small Particles" by Bohren and Huffman. The derivation of the formulas is fine, but I'm stuck ...
0
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0answers
17 views

What is special about the orbitals of iron, nickel and cobalt to make them ferromagentic? [duplicate]

Ferromagnetism depends on the arrangement of orbitals and spin in the valence electrons of an atom (below its Curie point). But what is so special about the orbitals of iron, nickel and cobalt, to ...
1
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0answers
18 views

With the help of a given charge is it possible to obtain a charge many times greater in magnitude

Consider a spherically conducting sphere. If a charge(say positive) is placed near the sphere, then it will lead to separation of charges inside the sphere.My question is, can we create charges more ...
1
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1answer
31 views

Magnetic field lines are not perfectly straight between magnetic poles

Why is fringing between magnetic poles inevitable? The diagram given below is the incorrect representation of magnetic field lines between two poles:
0
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1answer
35 views

Surface potential and work function

I am quite confused to the manifestation of an electric field on the surface of a metal due to the work function. Can anyone give me an intuitive answer behind this? For example: So I am studying ...
0
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2answers
3k views

Landau Levels and Magnetic length

I am looking into Landau Levels and keep coming across a magnetic length defined as follows for a 2D system: $l_B=\sqrt{\frac{\hbar c}{e B}}$ I have seen numerous sources say this is: $l_B\approx ...
0
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0answers
13 views

Polarity of emf induced in open circuits

In a closed circuit, current induced is in such a direction that it opposes the change in magnetic flux. In case of an open circuit like a metallic rod, which end of it will have the higher potential? ...
2
votes
1answer
117 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? ...
-1
votes
0answers
28 views

What is the electric field in medium 2 if the medium 1 contains an electron?

I have got this strange yet trivial problem. Say, there's an electron inside medium 1. Outside the medium, lets say we have medium 2. What is the electric field at any point in medium 2 due to the ...
0
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3answers
239 views

What determines the magnitude of force of an electromagnet?

Let's assume that there is an electromagnet with $B = 1 Tesla$ , what is the magnitude of the force it could generate on other dipoles equal to it's surface area? Can the magnitude of force (in ...
12
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4answers
2k views

Why should Conservative forces have their curl equal to zero?(intuition)

There are several conditions that must be met in order for a force to be conservative. One of them is that the curl of that force must be equal to zero? What is the physical intuition behind this? If ...
1
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1answer
30 views

At what times is the energy in an LC oscillator completely electric or completely magnetic?

I know that the time period of the LC oscillations is given by $T=2\pi\sqrt{LC}$. At what times is the total energy of the circuit completely stored in the capacitor or completely in the inductor?
0
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1answer
20 views

What is the physical significance of the area and shape of hysteresis curve of ferromagnetic materials?

Why do some materials have thinner/broader hysteresis curves than others and what does this difference in shape imply in terms of magnetic properties of the substances? Is there any significance to ...
35
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4answers
1k views

Is there an underlying physical reason why the Coriolis force is similar to the magnetic component of the Lorentz force?

I couldn't help but notice that the expression for the magnetic component of the Lorentz force, $$\mathbf F = q\,\mathbf v \times \mathbf B\,,$$ is very similar in its mathematical form to the ...
1
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1answer
33 views

What is the source of the Curie point?

I'm seriously revisiting my knowledge on magnetism, and the Curie point has been both enlightening and mystifying. I understand what it does ((ferro)magnetism disappears above it), and have a faint ...
9
votes
6answers
1k views

What is the physical definition of causality?

Maxwell's equations give a physical relationship between the electric and magnetic fields $\vec E$, $\vec B$ at the same time, which some interpret as changes in one causes changes in the other etc. I ...
3
votes
3answers
499 views

How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...
3
votes
3answers
31k views

Using A.C or D.C to create an electromagnet

Does it matter if I use A.C or D.C as a source to create an electromagnet? Or Does it depend on the voltage of current? For example: I have a coil which has about 50 turns. If I use same amount of ...
1
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1answer
118 views

Induced current in open circuit and closed circuit

In a closed circuit, electric current is induced so as to oppose the changing magnetic flux as per conservation of energy. However, in open circuit, emf is induced across its ends. How it is related ...
0
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1answer
39 views

Is there any objective basis for the “south to north” directionality of magnetic fields?

While explaining magnets to some students, I just realized a very basic thing I never thought about: We often say that magnetic fields have a "direction", that magnetic field lines "exit" the north ...
0
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1answer
122 views

Does Faraday's law work both ways, and if so why don't we use d.c for a generator?

Faraday's law in the integral form can be stated as $V = -d\Phi/dt$, where the right-hand side represents the rate of change of the magnetic flux and the left the voltage difference. In other words, a ...
0
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0answers
27 views

Net magnetic field & magnetization on a ferromagnetic material

A ferromagnetic materiel is saturated by an exterior magnetic field like so: Where $B_1$ is a uniform magnetic field. Then after some time $t$ another magnetic field $B_2$ is introduced as well, ...
1
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2answers
120 views

Why does the electric polarisation (polarisation density) have this direction?

It can be inferred that the amount polarisation $ P $ is dependent upon and proportional to the magnitude of the electric field $ E $ applied: \begin{equation} P \propto E. \end{equation} This ...
3
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2answers
3k views

Why is bandwidth, range of frequencies, important when sending wave signals, such as in radio?

So in wired/wireless networking and radio, signals are sent in form of wave. Then the concept of bandwidth comes in, which is the difference between highest frequency and lowest frequency in a signal. ...
1
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0answers
36 views

Gravity Theory Question [closed]

Three Questions: Is the Modern Five Dimension Theory of gravity an adaptation of Einstein's relativity theory? If so, can it allow us to accurately predict the movement, speed and direction of ...
0
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1answer
998 views

Electric field from conductive to dielectric media

I am interested in the main difference between transitions from electric fields from Conductive to Conductive/ Dielectric to Dielectric and Dielectric/Conductive media. What are the boundary ...
0
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0answers
16 views

What metal can be used as electromagnet core to attract a permanent magnet?

ok. Here are the requirements: 1.The core should not be attracted to permanent magnet when idle(like stainless steel), 2.Should act as electromagnet core with better permeability(like iron). Is ...
1
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1answer
41 views

Why does a magnet loose magnetic strength when heated?

Magnet manufacturing companies, for example Dexter Magnetic Technologies do not hesitate to explain the effects of heat upon magnets - citing how it degenerates the magnetic properties with levels of ...
0
votes
1answer
142 views

Magnetic field in-between two antiparallel wires with the same current

If I have two antiparallel wires with the same current at distance $2a$ apart from each other, how would I go about modeling the magnetic field in between the wires? I know the fields will add but I'm ...
1
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2answers
114 views

Scalar and Vector Potential

I am a physics undergraduate student currently studying electromagnetics. I have previously studied electrostatics and magnetostatics yet the concept of scalar potential, $V$ and the vector potential, ...
0
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1answer
28 views

Magnetic field and magnetic domains

I have a confusion regarding how magnetic field propagate in a medium (ferromagnets or air etc..). It is knows when a ferromagnet is exposed to an external magnetic field, the magnetic domain of the ...
1
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3answers
173 views

Maxwell's equations - underdetermined - uniqueness

Maxwell's equations can be seen as two dynamical equations (the two curl equations), and two constraint equations (the two divergence equations). So we have 6 unknowns ($E_x,E_y,E_z,B_x,B_y,B_z$). ...
1
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1answer
814 views

Forces on a wire moving in a magnetic field?

When a wire is placed inside a magnetic field and current starts to flow in that wire, that wire experiences the Lorentz force = $IL \times B$ and beings to move. Aside from induced motional - ...
1
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0answers
27 views

Attraction between electromagnet and a permanent magnet - at which point is the force the strongest?

You have an air-core inductor with current applied, so that the magnet in the picture will be attracted to it. At what position will the force between the two be the strongest and at which the ...
0
votes
1answer
26 views

Imaginary component in capacitive reactance

This is a trivial question in first year but, unfortunately, this popped up in an elementary yet compulsory lab experiment. The capacitive reactance is defined as $$X_{c}=\frac{1}{\omega c}$$ The ...
5
votes
1answer
768 views

Magnetic Levitation : Confusion with Lenz's Law

Considering the above diagram, I am failing to see why the aluminium ring floats upwards rather than oscillates. I understand Faraday's law, but I am struggling with Lenz's law - as there is an ...
3
votes
4answers
159 views

How can we prove charge invariance under Lorentz Transformation?

We have gravitational force between two massive particles and we have electromagnetic force between two charged particles. When special relativity suggests that mass is not an invariant quantity why ...
2
votes
2answers
129 views

Reference frequency

In my experiment, I have to obtain a relation between magnetic field of a solenoid and the applied Vp-p. The setup is as follows. http://www.teachspin.com/instruments/faraday/ Does my choice of ...
3
votes
2answers
251 views

Why is infrared radiation associated with heat?

I am little confused with infrared radiation. I understand that when an object is hotter, it radiates electromagnetic waves of a bigger frequency and this waves are also more energetic, that is why ...
0
votes
2answers
2k views

Why is a paramagnetic material attracted into a magnetic field?

I want to start by saying I've seen this topic: Attraction and repulsion of Magnetic materials and its supposed duplicates and it hasn't helped me very much. In the book Introduction to ...
0
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1answer
699 views

How does the magnetic field get induced in car's tire?

I was amazed to see how my car's tire started attracting the nuts and bolts, how in the world did it induce the magnetic field? Never heard of such phenomena!!!
-2
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1answer
24 views

C60 Macro Ojects

What would happen if you could make a ball or hollowed geometric shaped say the size of a basketball made out of C60.. due to its superconductivity could it have exotic or anti- effects on gravity and ...
45
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7answers
4k views

Do Maxwell's Equations overdetermine the electric and magnetic fields?

Maxwell's equations specify two vector and two scalar (differential) equations. That implies 8 components in the equations. But between vector fields $\vec{E}=(E_x,E_y,E_z)$ and ...