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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2
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1answer
66 views

“And God said…and there was light.” What does these equations mean? [duplicate]

Today while I was on the Internet I came across an interesting picture, that caught my eye. It's : I don't have to explain why this picture seems interesting to someone who knows the meaning and ...
0
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0answers
13 views

Landau levels. Gauge symmetry

If we try to find wave function for different vector potential, we will get wave functions, that do not have the same probability at any point( $|\psi_{E,p_y,p_z}|^2 \neq |\psi_{E,p_x,p_z}|^2)$ For ...
0
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1answer
18 views

Wave guide boundary conditions

Why only the normal component of Electric field and the parallel component of Magnetic field exist at the surface of a wave guide or any conductor?
0
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1answer
51 views

Possible dangers of power lines radiation, wi-fi and gsm technology [on hold]

I'd like to know more about the topic mentioned in the title. I have 3 questions. I'd be happy to hear your thoughts on any of those. So if high voltage power lines can cause harm to a human in some ...
0
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2answers
82 views

Where does the permittivity of free space constant come from

Does anyone know why the permittivity of free space is defined as: $\epsilon_0 = \frac{1}{\mu_0 c^2}$ ?
0
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1answer
30 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.
0
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1answer
63 views

close or open circuit?

A electric source provides a non electrostatic influence on the charges inside the source which pushes the positive charges from the negative terminal to the positive one. Does this happen when the ...
0
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0answers
35 views

How to simulate 2 AC electrodes putting into a pool in Maxwell3D (ANSOFT)? [on hold]

I am using Ansoft Maxwell3D to simulate the magnetic field produced by an AC current flowing through a water channel. Suppose i have 2 AC electrodes putting at two ends of a water channel or a pool ...
3
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0answers
51 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 ...
2
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3answers
45 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 ...
0
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1answer
37 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 ...
0
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1answer
40 views

Equation of Trajectory [on hold]

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
votes
2answers
65 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 ...
1
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0answers
29 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 ...
0
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1answer
67 views

Why does the superposition principle work? [on hold]

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? ...
6
votes
4answers
166 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 ...
0
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1answer
34 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?
3
votes
1answer
54 views

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

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 ...
1
vote
0answers
62 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 ...
-1
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0answers
20 views

Magnetic field direction, Lorentz force direction?

I know that the direction of current flow can change the direction of Lorentz force, what about the direction of the magnetic field? Also, for induced current due to electromagnetic induction is the ...
1
vote
2answers
42 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 ...
0
votes
1answer
45 views

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

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} = ...
-2
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0answers
43 views

Discharging an electric field

Is it possible to discharge an electric field without removing the power source? I understand that electric fields have a positive charge so would it be possible to use an earthed coil to discharge ...
0
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0answers
22 views

Magnetic field due to wire and plane [closed]

Suppose we have a wire with some current $I$ and which at a point $o$ spreads radially in all direction along conducting plane perpendicular to wire so what will be magnetic field at above and below ...
0
votes
1answer
29 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 ...
-1
votes
0answers
39 views

How to derive the light pressure from maxwell equations? [closed]

Is there any reference? Was the idea of radiation pressure known to Maxwell himself?
0
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0answers
43 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 ...
1
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0answers
18 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 ...
0
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0answers
25 views

Short Wave UV lamp [closed]

if I remember correctly, shortwave UV is very dangerous such that it can break DNA apart. Today I found this site, where parent can buy some scientific tools for their kids. Do not you think shortwave ...
1
vote
2answers
74 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.
1
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1answer
105 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
votes
1answer
41 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, ...
0
votes
1answer
48 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
vote
1answer
43 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
vote
1answer
51 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
votes
3answers
120 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 ...
1
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0answers
53 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 ...
1
vote
3answers
93 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 ...
0
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0answers
22 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 ...
0
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0answers
17 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 ...
0
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0answers
47 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" ...
0
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0answers
27 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?
0
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0answers
31 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, ...
0
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1answer
55 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?
0
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3answers
37 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
106 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
vote
1answer
46 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 ...
0
votes
0answers
30 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 ...
0
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0answers
49 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
vote
0answers
50 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 ...