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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57 views

How much does the magnetic force change in a solenoid with the distance between turns?

I was looking for answer in my physics book and in Internet but not. I guess that more distance should be an smaller magnetic field but I do not know how much.
3
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0answers
125 views

Biot-Savart for current carrying wire

A homework question has made me doubt my understanding of the application of the Biot-Savart law. Question: The magnetic field 43.0 cm away from a long, straight wire carrying current 5.00 A is ...
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3answers
59 views

Different frequencies working together

How do the different waves of EM spectrum present in the environment not interfere with each other? If they do, how does everything work properly? The radio waves of mobile phones and wi-fi work ...
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1answer
51 views

For AC current is it better to have a solid or a strandled wire?

For alternating current in wires there are two effects that make energy losses (increase effective resistance): Skin effect which comes since alternating current produces alternating magnetic field ...
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1answer
143 views

Equation of Trajectory [closed]

I was reading about Lorentz force law and motion of a charged particle under Electric field or magnetic field and I understood how they move in it. But as I was moving further I came across the ...
3
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2answers
100 views

How does the magnetic field gain energy through the induced non-conservative electric field?

This is a further question derived from this question about storing energy in an inductor. The accepted answer showed that, during the current increasing, it is the induced non-conservative electric ...
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0answers
34 views

Near Infrared for distance determination

Would near-infrared be an efficient frequency to use in determining the distance from the source of the infrared signal to an object, maybe in the range of 5 to 20 meters away? I need a formula for ...
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1answer
125 views

Why does the superposition principle work? [closed]

I am reading Feynman volume 2. (I was reading Griffiths at first.) I don't really understand why the superposition principle of electrical forces (or fields) works. Is there anything deeper in that? ...
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5answers
2k views

Difference between spin and polarization of a photon

I understand how one associates the spin of a quantum particle, e.g. of a photon, with intrinsic angular momentum. And in electromagnetism I have always understood the polarization of an EM wave as ...
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1answer
49 views

In which direction due to a polarizing grid the photon's electric field is oriented?

After a photon passes the slit, is it's electric field oriented perpendicular or parallel to the slit and why this is so?
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1answer
79 views

What topics do I need to study electromagnetism on the quantum scale? [closed]

What topics do I need to study (in order) so that I can study electromagnetics on the quantum scale? What is the name of the discipline studying electromagnetism on the quantum scale? Do I need to ...
4
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3answers
388 views

How are the Lorentz force, Maxwell's third law and Faraday's law of induction clasically related?

Faraday's law of induction can be used in any situation where the magnetic flux is changing through a closed conducting loop. While giving the correct answer, it seems to me that for the following ...
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2answers
52 views

Is there a material that could “convert” near infrared frequency to infrared?

I have a laser with a wavelength of 650 nm (visible red light) and was wondering if there is some sort of material that could be used to absorb and disperse a different frequency of light around (900 ...
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1answer
61 views

How one can know the gauge field emerging from the local gauge invariance is actually the EM field? [closed]

How one can know the gauge field emerging from the local gauge invariance is actually the EM field? I understood in a simple scalar field whose Lagrangian is given by $ \mathcal{L} = ...
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1answer
43 views

What unit of distance to use when calculating power loss?

80% of Earth's atmosphere is within 10 miles of Earth's surface. I know that power attenuates inversely as the square of the distance within the atmosphere so it occurs to me that a 50,000 watt signal ...
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0answers
83 views

Speed of a magnet

What is the speed of two magnets during the congruent moment of their attraction? Theoretically, could a large enough magnet attract a significantly smaller magnet at near the speed of light? In ...
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0answers
67 views

Mutual inductance theoretically decreasing while EMF is increasing in 2 square coil system

I have a quick question regarding electricity and magnetism. I am measuring the induced emf in a square coil of wire with an inductance of 439uH (the other coil is also 439uH and is the same shape). I ...
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3answers
256 views

What does amplitude in wavelength of light physically mean?What oscilates with time in photon?

Like amplitude in wavelength of water waves signify the displacement of water particles about their mean position.
3
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3answers
255 views

Electromagnetism Boundary condition

The dielectric slab surrounded by air as shown in diagram has permittivity $\epsilon$ different from air and permeability almost same as air. Electric field everywhere within the slab is given to be ...
2
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1answer
52 views

Can asymmetrical Lorentz forces account for Relativistic affects near the speed of light?

The underlying thought here is that at low relativistic speeds all objects are subjected to emf radiation from all directions. This is basically the sum of all the radiation (light, infra-red, ...
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1answer
89 views

A falling steel beam - Maximum induced voltage [closed]

I'd appreciate it if someone could explain how to answer this question: A 2 m long steel beam is falling from a height of 12,5 m. During the fall, the beam is oriented in an east-west direction. ...
1
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1answer
176 views

Transformers - Why more coils in second coil causes more voltage [duplicate]

I am learning about magnetic induction and transformers. I have coil1 which uses AC to create an oscillating magnetic field. I have ...
1
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2answers
157 views

How does electromotive force (emf) influence electrostatic force in a circuit?

I am learning about emf and I am using university physics of Hugh D. Young which states that when the emf source is not part of a circuit the non-electrostatic force of the source moves charge form ...
3
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3answers
288 views

Derivation of the speed of light using the integral forms of Maxwell's Equations

Having just finished physics 2, I've been (slightly) exposed to showing that light is a wave with speed $1/\sqrt{\mu _0 \epsilon _0 }$ using the differential forms of Maxwell's equations, though this ...
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0answers
74 views

Getting the electric field using Green's function [closed]

Let the Green's function for the gauge field be given (after gauge fixing) as $$G_{\mu \nu}(x,y) = \delta_{\mu \nu}G(x-y) \tag{1}$$ where $$G(x-y)= \int \frac{d^dk}{(2\pi)^d} \frac{e^{ik \cdot ...
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3answers
146 views

Plane waves - EM wave

An accelerating electric charge will emit transverse electromagnetic waves. These waves are propagating away in wave fronts that become flatter and flatter as getting further from the source. So they ...
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0answers
54 views

Free vs Bound Charges, especially in metals

Are conduction band electrons in metals generally considered free charges or bound charges for E&M purposes? I'm not asking about freedom in the sense of being able to escape the potential well ...
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0answers
20 views

How the magnet moves without pushing? [duplicate]

I video on Youtube represents that it can move through a coil without providing any external force and it seems that the force arises from the lines of forces generated in the coil. How can we ...
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0answers
142 views

Could the explanation for this simple electric train be attributed to Lenz's Law?

There is a discussion of a Youtube video where a battery with magnets attached at either end moves through a copper coil. It has been commented on in the Phys.SE post How does this "simple" ...
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0answers
46 views

Why spin-$\frac{1}{2}$ nuclei have zero electric quadrupole moment?

Why spin-$\frac{1}{2}$ nuclei have zero electric quadrupole moment? How to calculate in general?
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0answers
47 views

Parity of magnetic susceptibility $\chi(\omega)$

It is well known that real and imaginary parts of magnetic susceptbility, defined as $\chi=\chi'(\omega)-\mathrm{i}\chi''(\omega)$, ought to be even and odd to frequency $\omega$ respectively, ...
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1answer
72 views

Does reflected light change LED power consumption?

If I enclose an LED in "tin foil" so that the photons it gives off are reflected back to it, would the power consumed by the LED go down?
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2answers
172 views

Currents induced by rotation of a coil about magnetic field lines

If the coil on the left is rotated about the magnetic field lines, will there be an induced current? I know that the flux concerns only the component of the magnetic field perpendicular to the ...
2
votes
4answers
195 views

How to find the magnetic field around a wire with the full time dependent Maxwell Equations? [closed]

In all textbooks the magnetic field around a wire carrying a current is found from Ampere's Law. However, I would like to know what the expression for the magnetic field is, using the full ...
1
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1answer
50 views

How to get second order equation for spinor (derivation from Dirac equation)?

Dirac equation with an Abelian symmetry can be written as $$(\gamma^{\mu}D_{\mu} - m)\psi = 0$$ where $$D_{\mu}\psi = (\partial_{\mu} - iqA_{\mu})\psi$$ Then how do we get this second order equation ...
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0answers
33 views

Insignificant Potential difference?

Is it possible, that a conductor with an extremely short length, say $1\text{mm}$ or less passing a magnetic field of $1T$ with a reasonable velocity of $20\text{m}/\text{s}$ would induce little to no ...
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0answers
123 views

Why is electric charge the conserved quantity corresponding to global $U(1)$ symmetry? [duplicate]

An example of a symmetry transformation for certain Lagrangians (notably the canonical complex scalar field Lagrangian) is multiplication of the fields by a complex phase. When we multiply the fields ...
1
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0answers
76 views

Electromagnetic mass of a continuous charge distribution [closed]

I am trying to understand if it is possible to have a consistent solution to Maxwell's equations and Lorentz force equation simultaneously with no other forces present. The Lorentz force density is ...
2
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0answers
55 views

What is “above” and what is “below” the surface of a sphere?

When studying Electromagnetism using D.J. Griffith's Introduction to Electrodynamics, the boundary conditions for the electric potential across a surface charge density are expressed using the normal ...
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3answers
80 views

Does there exist a hyperbolic relationship between frequency $\omega$ and wavenumber $k$?

As the title states, is it possible to derive a hyperbolic relationship in the form of $\frac{x^2}{a^2} - \frac{y^2}{b^2} = 1$ between frequency $\omega$ and wavenumber $k$ I have tried to start this ...
3
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2answers
163 views

Do the fields exist without electric charges? [closed]

I read in an old book on electrodynamics by Pauli that theoretically there does not exist any need of charges to be there. Fields can even exist without the charges but still independent fields ...
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0answers
27 views

Fresnel equations of reflection applied to microparticles

I wanted to know if the Fresnel equations of reflection, as described here, can be used to calculate the reflectance on the interface of particles which have a diameter near the size of the wavelength ...
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0answers
58 views

Basic question in electromagnetic duality

In electromagnetic duality, where does this relation come from? $$\overrightarrow{E} \rightarrow \cos \alpha\overrightarrow{E} - \sin \alpha\overrightarrow{ B}$$ $$\overrightarrow{B} \rightarrow \cos ...
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0answers
39 views

Electromagnetic duality and (electric induction D and magnetic intensity H)

We originally have $$\overrightarrow{\nabla}\cdot\overrightarrow{B} = 0$$ $$\overrightarrow{\nabla}\times\overrightarrow{E} = -\frac{\partial \overrightarrow B}{\partial t}$$ When electromagnetic ...
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2answers
74 views

Why is electricity 'the screwing force'?

In one of his lectures Richard Feynman, a great genius and a 'naughty Bronx kid', refers to to the Coulomb force, electricity as "the screwing force". Apart from the obvious joke and double entendre, ...
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1answer
96 views

What are the physical interpretations of $\nabla \times \textbf{P}$ and $\nabla \cdot \textbf{M}$?

In the text I am reading, it is made clear that it is incorrect to assume that the electric displacement $\textbf{D}$ is identical to the electric field with the exception that it is raised from the ...
0
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0answers
36 views

Vector potential in presence of monopole [duplicate]

In this paper http://www.hcs.harvard.edu/~jus/0302/song.pdf when Song was explaining dirac string. He said "In the presence of a magnetic monopole, the vector potential cannot be defined everywhere. ...
0
votes
1answer
68 views

I wnt to know HOW to create TM, TE, and TEM waves; and is it being used in industry? [closed]

Transverse Magnetic (TM) and Transverse Electric (TE) modes So I'm wholly ignorant of any knowledge surrounding these modes, so bear with me here.. One component is infinitesimally small in the ...
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1answer
211 views

What's the relationship between velocity factor and refractive index?

Wikipedia on velocity factor explains: For optical signals, the velocity factor is the reciprocal of the refractive index. On refractive index, Wikipedia also has an explanation of refractive ...
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3answers
778 views

Why do we use the Coulomb potential for the hydrogen atom?

When solving the Schrodinger equation for the hydrogen atom, the Coulomb potential $V = \frac{e^2}{4 \pi \epsilon_0 r}$ is used. The Coulomb potential comes from classical electrodynamics, so why ...