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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38 views

Do magnets\ magnetic fields become weaker when exposed to para magnetic objects?

Do magnets (permanent) become weaker as they are exposed to para-magnetic objects? I was thinking about this after seeing this. I am buying a magnet and wish to know if a magnet (permanent) loses its ...
3
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1answer
36 views

What topics do I need to study to study electromagnetics 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 of studying electromagnetics on the quantum scale? Do I need ...
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0answers
33 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 ...
3
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2answers
93 views

Prove Biot-Savart law, assuming that $\vec{A}=\frac I c\int \frac{d\vec{L}}{r}$

Prove Biot-Savart law, assuming that $$\vec{A}=\frac I c\int \frac{d\vec{L}}{r}$$ $$\vec{B}=\nabla\times \vec{A}$$ Any hint on what to do next?
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3answers
3k views

Can a light be bent by a magnetic field?

I'm struck with two competing ideas on the question in the title. Listing #1: http://van.physics.illinois.edu/qa/listing.php?id=2009 Q: "How far can a magnetic field bend light?" A: "Unfortunately, ...
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2answers
40 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
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2answers
123 views

Magnetic field by a solenoid?

I am really not able to understand why is it that the current,while finding the magnetic field in the solenoid (ideal one), is not $I$ the current flowing throught the solenoid but $nI$, where $n$ is ...
2
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3answers
221 views

Why is the inner product between divergence-free current$\vec{J}$, (satisfied $\nabla\cdot\vec{J}=0$) and a gradient field$\nabla \varphi$ zero?

I read a statement saying that the inner product between divergence-free current and a gradient field is zero. Divergence-free surface current is $\nabla\cdot\vec{J}=0$, and $\vec{J}$ could be ...
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0answers
18 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 ...
0
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1answer
46 views

Does inducing charge on a grounded conductor do work?

Imagine a grounded conductor as an plane of infinite area. If I bring a charge to a close proximity to the plane, it induces some charge distribution on the conductor. The question is: is any work ...
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1answer
76 views

Can I tune a magnetic field to conduct heat from a rotating object?

Is there a way to transfer heat from a rotating object made of iron into a suitable heat sink using a magnetic field as a transfer medium?
1
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1answer
201 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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3answers
79 views

Why can't unequal current sources be connected in series?

Imagine two power sources: PS-1 that can supply $5A$ at $100V$, and PS-2 can supply $10A$ at $40V$. Due to conservation of charge and Kirchoff's current law (KCL), this is incorrect, and would lead ...
0
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1answer
42 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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3answers
1k views

How is electromagnetic wave variation distributed in space?

Imagine an electromagnetic wave (a monochromatic one for example). The electric field amplitude and its variations travel in the propagation direction. So, if there really exists a propagation ...
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3answers
180 views
+100

Is the magnetic field of a white-dwarf merely residual?

Follow-up to my other question How does Sol's magnetic field continue to exist at such high temperatures? Assuming Sol's magnetic field is generated by convective currents in it's plasma, how is ...
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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
21 views

Magnetic field due to wire and plane [on hold]

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 ...
7
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1answer
169 views

Electric Field Change Freezing Temperature of Water?

I assume that the reason water freezes is because as you decrease the temperature, the kinetic energy of the water molecules decreases and the dipole bonding potential eventually over comes the escape ...
1
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1answer
61 views

What is the sum of the electrons' magnetic moments in a wire?

The electron has a magnetic moment. This magnetic moment will be influenced in a electric field; the magnetic moments will be more or less aligned. During the movement of an electron in a wire under ...
0
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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
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2answers
46 views

Deflection of magnetic compass sorrounded by alternating poles

What happens to the deflection of the magnetic compass if it is surrounded by south poles and north poles in alternating direction of a magnet around it in a circular pattern. Will it be deflected in ...
7
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2answers
264 views

The gauge covariant derivative and its substitution

I was wondering wether it would make a difference (in general) if I were to were introduce the gauge covariant derivative $$D_\mu=\partial_\mu+ieA_\mu$$ In the Lagrangian density and then derive the ...
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0answers
38 views

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

Is there any reference? Was the idea of radiation pressure known to Maxwell himself?
0
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1answer
269 views

How to calculate flux density in a toroidal CT that has an electrical line pass through the center?

I have seen the Biot–Savart equation, but I don't know how to apply it. Does the conductor length need to be considered finite and equal to the core length, or will the calculation be for a conductor ...
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2answers
99 views

Moving frames - a blow on “virtual particles”?

There is a polemic about whether virtual particles EXIST, or are only a tool for making our calculi easier. Here is a doubt about their existence, and on the other hand, an argument in support of ...
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2answers
1k views

Potential energy from opposing magnets repelling each other with a gap of 1 mm

I have two powerful rare earth magnets, that are separated by a distance of 1 mm. I applied energy to bring them closer to each other, hence increasing the potential energy. Now, when one of the ...
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0answers
42 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
16 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
24 views

Short Wave UV lamp [on hold]

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 ...
0
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1answer
71 views

Why do we always consider the area of inner solenoid while calculating the mutual inductance of two coaxial solenoids?

While we know that flux linked to an area is the dot product of the area vector of the loop(and not the actual area encountering the field lines) and the magnetic field linked to it, why then do we ...
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2answers
69 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
102 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 ...
0
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1answer
75 views

How is Magnetic force on a current carrying conductor $Blb$

I was reading an answer about torque acting on a rectangular current carrying loop kept in a uniform magnitude field B. Force acting on each sides is $F_1$, $F_2$, $F_3$, $F_4$. It's written here : ...
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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, ...
24
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6answers
5k views

Does a magnetic field do work on an intrinsic magnetic dipole?

When you release a magnetic dipole in a nonuniform magnetic field, it will accelerate. I understand that for current loops (and other such macroscopic objects) the magnetic moment comes from moving ...
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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 ...
2
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1answer
39 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
54 views

calculating electrodynamic momentum of a dumbbell (consisting of two point charges) in longitudinal motion

I'm working through a paper on momentum in electrodynamics that requires the integration below and would greatly appreciate any help. I'm pretty sure it evaluates to $2/d$ but I can't quite figure ...
0
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3answers
36 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 ...
0
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1answer
46 views

A falling steel beam - Maximum induced voltage [on hold]

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
49 views

Magnetic field of a static disk magnet

I have a magnetic disk (Radius R, height h) that creates magnetic field lines (axisymmetrical). I simulated the field lines, exported the data and am now trying to fit a function into the data to have ...
3
votes
1answer
66 views

Earnshaw Theorem for ionic solids

Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable? How can I reason this based on Earnshaw's theorem?
0
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1answer
72 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 ...
3
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3answers
117 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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1answer
47 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 ...
1
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1answer
42 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 ...
0
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2answers
131 views

Why is emf equal to PD when circuit is “open”?

I understand that the set up of a battery consists of very good, but not ideal conductor, and therefore, some internal resistance exists. Also, I get that emf is the PD that would exist if the ...
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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 ...
2
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3answers
303 views

Potential difference with an inductor

As far as I know, the potential difference between two points is defined as the negative line integral of electric field between those 2 points: $$\Delta V=-\int d \ell\cdot\mathbf E$$ I also know ...