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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Can we shield a certain region of space from magnetic field? [duplicate]

Recently I learnt about shielding a region of space from an electric filed. I wondered if the same can happen for magnetic field.
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29 views

Why does excess of charge in an isolated conductor move to the surface?

A remark in my textbook goes as follows: "If an excess charge is placed on an isolated conductor, that amount of charge will move entirely to the surface of the conductor. None of the excess charge ...
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0answers
67 views

What does the net force do with this droplet in magnetic field?

Consider a spherical droplet with radious $R_d$ which is coated with an immiscible ferrofluid with volume equal to $2v_f$ (shown dark in Fig. 1). While the droplet is in rest on a surface, if I ...
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7answers
1k views

Why aren't there compression waves in electromagnetic fields?

I just started learning about optics, and in the book I'm reading they explain how the electrical field caused by a single charged particle could be described by a series of field lines, and compare ...
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2answers
139 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
138 views

Looking for lists of student difficulties with electromagnetism, circuits (DC and AC)

I'm trying to help with an Instructor's Guide for an introductory calc-based physics text, and it would really help if I could locate some lists of typical student difficulties with topics like ... ...
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30 views

What do you call this “asymmetric polarization”?

I am considering this unusual polarization of EM waves: which travels in the x-direction and has magnetic and electric fields as shown. This can be produced by non-oscillatory currents. What name ...
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3answers
124 views

Induced “Potential Difference” in Loop/How do Voltmeters work?

Say we have a single, solid circular loop of wire rotating at a constant angular velocity in a uniform magnetic field. There is an induced EMF creating a current in the wire. At the absolute ...
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1answer
45 views

Calculating flux of axisymmetric electric field through a sphere [closed]

The following problem and its solution is taken from I. E. Irodov's book basic laws of electromagnetism : I do not understand how the fact that field is axisymmetric leads to the conclusion that ...
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9 views

Field strength of a discrete solenoid

First, I want to clarify that I mean a solenoid made by coiling a fine wire, and not the type made from a continuous piece of conductive material. That said, I know I can find the magnetic field ...
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3answers
2k views

Popular depictions of electromagnetic wave: is there an error?

Here are some depictions of electromagnetic wave, similar to the depictions in other places: Isn't there an error? It is logical to presume that the electric field should have maximum when ...
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4answers
164 views

The fainter the star, the further away it is?

If a star appears to be very faint, would it imply that it's really far away or that it's luminosity is minimum?
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2answers
316 views

Evidence for electrodynamics in curved spacetime

Field theories in curved spacetime is usually formulated by integrating their Lagrangian over the curved spacetime. For example, for electrodynamics, we have the action $$ S = \int d^4x \left( ...
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1answer
40 views

How to get the magnetic field strength in space near a solenoid

I am trying to find the magnetic field strength along the axis of a solenoid. If I know the strength of the field at the center of the solenoid, and I know the distance from the center of the ...
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2answers
222 views

What happens when you pass a current through a coil made of a ferromagnetic substance?

I know when you pass a current through a length of copper coil or a solenoid, there is the induction of a magnetic flux. But what of the coil made of the ferromagnetic material, the permanent type ...
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1answer
104 views

Why quantum electrodynamics? [duplicate]

Most of the people seem pretty much content with classical electromagnetic theory .And most of the applications use classical EM theory .However, in such situations I would like to know what was the ...
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0answers
28 views

Can a charge moving in an open trajectory qualify as current?

It is sometimes said that a point charge is equivalent to an electric current. If it were a steady current, I should be able to find it from Ampere’s law or Biot-Savart’s law. Even if the current is ...
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1answer
41 views

Magnet and electromagnetic wave, and speed of light

I have this practice exam question: T or F. If you hold a magnet in your hand and wave it back and forth, you will create an electromagnetic wave that moves away from your hand at the speed of ...
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3answers
134 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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3answers
97 views

How is energy conserved in magnet?

When an object (i.e.magnetic) is attracted towards the magnet, work is done so that the energy is used but from where this energy comes from?
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34 views

If gravitational field has negative energy density, how does gravitational radiation carry positive energy?

The following question uses the analogy between EM (electromagnetism) and GM (gravitomagnetism). In order to force two like electric charges nearby, some work has to be done. This implies that the ...
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1answer
148 views

Remote EEG Detection / Reading

I recently noted that Phillips, Accenture, and Emotive grouped together to create a proof of concept that would assist ALS patients to gain greater control of their lives through brain, voice, and eye ...
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2answers
85 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 ...
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1answer
918 views

Why magnetic field lines and force are not orthogonal with magnets?

The below explanation why magnetism exists is superb in this video. The explanation about magnets is also great in this video. A magnet has atoms with unpaired electrons forming mini magnets. The ...
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1answer
249 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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36 views

Derivable Concepts in Mechanics and Electromagnetism

In Classical Mechanics, one of the possible foundations is based on three concepts aka mass(equivalent to energy), length and time. This is a foundation because we can model everything ( pressure, ...
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189 views

Why doesn't an electromagnetic wave violate conservation of energy?

I'm starting to study electromagnetic waves and as i understand, an electromagnetic wave projects a varying electric field. This electric field can in turn give forces of repulsion/attractions to the ...
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3answers
2k views

Is there any example where electric and magnetic fields are not perpendicular?

Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
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76 views

Proof that electric and magnetic fields in a EM wave are perpendicular

Is there a general proof, that for electromagnetic waves the magnetic and electric fields are perpendicular? The only ones I can find only focus on plane waves.
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1answer
213 views

Why is Terahertz radiation so hard to generate?

This paper (and many others I've read) claim that searching for ways of producing THz radiation is a high-interest research topic. However, something I've just never understood is why it's so hard ...
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3answers
5k views

Reducing Eddy current losses

Eddy currents are setup in any metallic block which is in the vicinity of changing magnetic fluxes. These primarily cause heat losses, and in certain cases causes damping of the relative motion ...
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2answers
60 views

Using Electric Potential to Float an Object

I've been trying to answer the following question but I'm stuck at one step. The question essentially states that a magician is trying to perform a "floating objects" act, for which she has a thin ...
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2answers
178 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
82 views

Ampère's law and superconductors

I have been reading about superconductors and emerge me a inquietude about the explanation of existence of currents inside the superconductor while their magnetic field (inside too) is zero. Based in ...
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1answer
30 views

Induced EMF of a rectangle loop?

If a rectangle loop would move inside a magnetic field, would the induced $\epsilon$ be zero? Why would it? Is it due to the induced $\epsilon$ canceling out? Being in series and in opposition? ...
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3answers
136 views

Faraday's law in a ring

What role does the induced emf in Faraday's law play in generating current in a ring in which the magnetic flux is changing ?
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65 views

Force on a loop with induced current

Consider an infinitely long ideal solenoid with current $I$, radius $a$, turns per unit length $n$. Put a closed conducting loop around it (radius $b > a$), on a common axis through their centers. ...
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1answer
60 views

Is what i think Magnetism is, Magnetism? [closed]

So, i was randomly thinking about magnets one day and decided to try and figure out what Magnetism actually is. This is what i came up with: Magnetism, the magnetic field of an object, is a form of ...
2
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1answer
2k views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
2
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0answers
26 views

Physical significance of toroidal moments

The electric field of a toroidal dipole moment $\vec t$ is the same as the electric field of a electric dipole moment $\vec p$, except that it is scaled with the factor $ik$. The $i$ makes the ...
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0answers
16 views

Mosotti-Clausius formula from the first principles

I would like to understand how to get the Mosotti-Clausius formula for the dielectric susceptibility of a dielectric material with spherically symmetric molecules from the first principles, where by ...
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0answers
29 views

Separating Aluminium sheets with magnetic field

all! I would like to know if it would be possible to induce a strong enough magnetic field in sheets of aluminium so they would be separated between each other, like when you use magnets to separate ...
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1answer
72 views

Why is there no induced electric field in the experiment (Faraday's Law)

Below are three circuit diagrams for each of Faraday's experiments that allowed Faraday to come up with Faraday's Law. In Griffiths' Introduction to Electrodynamics Griffiths states (on page 302 of ...
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2answers
117 views

Would a rotating magnet emit photons?

If a magnet is rotating, around an axis perpendicular to the axis north-south axis of the magnet (which I assume to be cylindrical symmetrical), in space (so no-gravity/freefall or friction), should ...
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0answers
23 views

Discrepancy between Sidebottom and Kittel's Solid State Textbooks

There seems to be some discrepancy between Sidebottom and Kittel in the value of the diamagnetic susceptibility of the hydrogen gas. Sidebottom states that it is $-2.2\times 10^{-9}$, while Kittel ...
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0answers
30 views

Why does charge build up at the boundary surface of two media?

On a homework problem, we are asked to to use the first two Maxwell equations, $$\nabla\cdot \mathbf{B} = 0$$ $$\nabla \cdot \mathbf{D} = \rho$$ to show that along the boundary surface of two ...
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3answers
709 views

Moving conducting bar in (changing) magnetic field

In my exam today I've been given this problem, yet even with the results at hand I simply can't warp my head around it; Given the picture below, a bar is placed on two conducting rails with a ...
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0answers
10 views

The movement of magnetic rings along a current carrying wire

The creation of circular magnetic rings around a direct current is easily illustrated by sprinkling iron filings onto a horizontal sheet, which has the conducting wire passing vertically through its ...
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2answers
134 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 ...
0
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1answer
53 views

How did Lenz derive his law?

I read about it but am not sure if it actually follows law of conservation of energy.I tried reading some reference books but could not find the derivation of the law.