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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What are diamagnets and paramagnets?

A paragraph in my text reads: An atom or ion with all electrons paired is not attracted by strong magnets and is termed 'diamagnetic'. In contrast, spins do not cancel when unpaired electrons are ...
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6 views

What is the meaning of dielectric constant with AC fields?

I understand that in the DC case for parallel plates, a dielectric constant tells you by what factor the electric field gets reduced in the dielectric material vs. in vacuum. Does the same ...
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10 views

how to build an anti proximity alarm [migrated]

I am trying to build an alarm that works in an opposite way to a security alarm in a shop. In shops RF tags on items set off an alarm as you walk through a detector. I wanted to build alarm that ...
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21 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
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0answers
33 views

Is there any other momentum besides the Poynting momentum stored in an electromagnetic field?

I am having some conceptual difficulties with energy and momentum stored in the EM field. The force density at a point is $\rho E + j\times B$ Because of conservation of momentum, and because the ...
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14 views

Magnetization of a type I superconductor

How could I derive an expression for the magnetization of a spherical type I superconductor? I've searched in many sites but I haven't found any way to proceed.
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1answer
34 views

Distance of electromagnetic waves based on frequency

I would like to ask your opinion regarding this matter: Based on the relation of frequency and wavelengths, the higher the frequency, the shorter the wavelengths and therefore the distance of travel ...
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2answers
636 views

How exactly does a solar flare cause a power line surge?

There are occasional large scale electrical blackouts caused by solar flares. Quebec Solar Flare Blackout My question is: what affects the severity of the problem? It obviously depends on the ...
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2answers
26 views

Quality Factor in a Parallel LC Circuit

I was wondering if there is a notion of a quality factor in a parallel LC circuit, since there is no resistance. One can show that this circuit has a resonance frequency as follows: Impedance: ...
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1answer
56 views

Advanced (undergraduate) book on electromagnetism [duplicate]

I am an undergrad student and i have been through a first easy course on electrodynamics and i have used the book of Griffiths which let me satisfied.But the next two courses I will be taking are ...
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1answer
15 views

understanding shceme field lines - magnetic field

I would like to know if the magnetic field is in "the x-y plane". Does this mean the field lines are actually parallel to the visible line x or y? Or does it mean the field lines are parallel to the ...
2
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1answer
47 views

If magnetic field cannot change velocity, what changes the velocity of a compass needle?

I am really confused after reading the properties of magnetic field. I thought magnets could speed up things when they attract them.
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16 views

Lifting capacity of superconductors

How does the strength of the magnetic field the superconductor is exposed to affect its ability to levitate/lock heavier objects? Or is there no relationship (for superconductors) between magnetic ...
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1answer
16 views

Electric force between 2 rods with different lengths carrying different currents

What is the electric force between tow rods with different lengths that carry currents $I_1$ and $I_2$? Indeed, by the use of the Biot-Savart law I obtained a relation to calculate it, but there is ...
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0answers
10 views

What voltage is induced between the endpoints of bar, if we swing it by an amplitude [on hold]

After a long horizontal conductor carrying current of 10 A is vertically suspended 2m long insulated conductive rod. We swing it by an amplitude of 10 cm. (a) in the direction of the wire; (b) in ...
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0answers
6 views

With what frequency triangle swings if it shuns from equilibrium? [on hold]

Guide V-shaped is with no friction in the swivel bearings A and B (see Fig.) Of the magnet with a vertical magnetic field of 0.8 T. The weight of the guide is 50 g, the length AB 4 cm, and the length ...
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2answers
58 views

Are spherical coordinates distances or angles?

I've become confused about spherical coordinates when dealing with electric fields. The way I always understood spherical coordinates is something like the below picture. To define a vector, you give ...
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1answer
30 views

Maxwell, speed of light and the electric permittivity and magnetic constants

When Maxwell found that the already-measured speed of light could also be derived from the already-measured electric and magnetic constants, what were the electric and magnetic constants measured to ...
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2answers
101 views

Solution of simple problems using only Maxwell equations in differential form

Solve simple electrostatic or magnetostatic problems using only Maxwell equations. For example: In every book there is an excercise to find a magnetic field outside a thin wire of radius $a$ with ...
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0answers
21 views

Is the Electric field around a loop on conducting wire always constant?

If a wire is subject to some arbitrarily changing magnetic flux inducing an electric field within, what is the E-field equal to? $\oint \vec{E} \cdot \vec{dl} = -\frac{d}{dt} \int \vec{B} \cdot ...
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1answer
26 views

Why isn't any current induced in a rectangular loop when it is moved in a uniform magnetic field with constant velocity?

It is said that the magnetic flux passing through the coil remains constant. But when the rectangular loop is moved out of field with constant velocity,then the magnetic flux decreases. Thus current ...
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0answers
24 views

Uniform field through a disc

Let us say that we have a magnetic field of the form $B_0 \sin(\omega t) \hat e_z$ in all space. Now let us say we put a conducting disc within this field. I want to find the electric field within ...
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2answers
82 views

Why does aluminium foil spark in the microwave? [duplicate]

I don't understand fully why aluminium foil sparks in a microwave oven? I think what is happening is the oven sets up an electric field, and the field induces a current in the foil (how?), and ...
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18 views

What is strength of an electromagnet at a distance?

I want to levitate a permanent magnet between two electromagnets. My two governing equations are: $$F = \frac{B^{2}A}{{2\mu_{0}}}\tag{1}$$ $$B = \frac{NI\mu}{L}\tag{2}$$ Where $x$ is the distance ...
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1answer
48 views

Electromagnetic cooling

Heat means stored kinetic energy in matter. Microwave owens and induction heaters works on increasing kinetic energy on matter. Is it possible to make inverse of this heaters like cooler. Can we ...
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0answers
24 views

In a system with a decaying magnetic field, is the induced E-field around the wire constant?

Below is an example problem that I know how to solve, particularly when the current is switched off and the magnetic field is allowed to decay. However, in systems typically like these, is it a far ...
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16 views

Magnetic field along the line which is perpendicular to the wires

Suppose we have 3 wires which cross at some point $A$. After the branching point, the electric currents in two arms are $I$. And we have the line passing through the point $A$ and perpendicular to the ...
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17 views

Calculate characteristic frequency from atomic polarizability

With Lorentz model, the plasma frequency can be calculated from electron density $$\omega_p=\sqrt\frac{4\pi N e^2}{3m}$$ But I also found in this paper that it could also be calculated from atomic ...
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22 views

understanding magnetic dipole moment and torque [on hold]

I would like yo know if I understand things correctly: Magnetic moment, which is a constant value for a solenoid or magnetic dipole, determines the torque it will experience in a magnetic field. (I ...
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1answer
34 views

What is the typical strength of the electric field in a particle accelerator?

I am working on a research project involving the closed orbits of hydrogen in the presence of an external electric field and I am curious what a reasonable approximation for the electric field ...
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1answer
38 views

Relativistic Lorentz Force with constant, perpendiuclar, and uniform E and B fields

I am trying to solve the following problem from the Fundamentals of Plasma Physics by Bittencourt (Problem 2.7): Analyze the motion of a relativistic charged particle in the presence of crossed ...
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0answers
19 views

A force in a homogeneous magnetic field [on hold]

Semi infinite parallel conductors, while on them without friction slides a crossbar . Perpendicular the plane of the conductors is a homogeneous magnetic field. To what extent of force we must act on ...
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3answers
99 views

What can change a photon's frequency?

I found this question: Is it possible to apply force to a light particle? As it states, gravity can change the frequency of light by changing its momentum. My question regards other phenomena that ...
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1answer
23 views

Current and current density

Current, $I$, is generalised as: $I=\iint_{A}^{} \vec{J}. d\vec{A}$. I know that current density always points in the direction of flow of positive charge. I wonder if the infinitesimal element, ...
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27 views

What exactly happens in an electric circuit?

After reading chapters on Electrostatics, I have been having lots of problems in understanding current electricity.I will be trying to tell what my problems are by telling what I already know.Please ...
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47 views

Why are cereals attracted by a magnet?

Many cereals (from the supermarket) are attracted by a magnet. This can be seen by crushing the cereals into a very fine powder and approaching a strong magnet. The usual explanation is that cereals ...
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2answers
40 views

Lorentz force Law

I want to ask a fundamental question about Lorentz force equation. Why is it important to incorporate both electric and magnetic forces into one single expression? I know magnetism is electricity's ...
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1answer
25 views

Constant charge density and magnetic field

Suppose we have an arbitrary number of point charges in a vacuum, described by a constant charge density $\rho$. Can they be the sources of a magnetic field $\mathbf{B}$? My intuition is that they ...
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1answer
36 views

Question about Gauss' law and dipoles

I've got a question about dipoles and Gauss' law: Consider an electric dipole $p=ql$ in free space, centred at the origin of a Cartesian reference frame. Using Gauss’s Law, discuss if the electric ...
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3answers
130 views

Technical question about 2-forms

A technical question about the electromagnetic tensor, but before that, it is know if, say, instead of being $$F_{\mu\nu}=\partial_{\mu}A_{\nu} - \partial_{\nu}A_{\mu}$$it were ...
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1answer
41 views

Why do magnets vibrate near an AC source?

Why do they vibrate and simply not get pulled closer or further from the source of emf? This may be related to the shape, but if I take a small N45 disc magnet and put it near an electrical ...
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20 views

What is the speed of the charge in this setup of spherical conductors? [on hold]

Two concentric spherical conductors respectively have radius $r_1 = 0.145\ \mathrm{m}$ and $r_2 = 0.207\ \mathrm{m}$. The inner sphere carries a charge of $-6.00 \cdot 10^{-8}\ \mathrm{C}$ . An ...
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1answer
39 views

Reflectivity of Metals - real and imaginary part of k-vector and complex dielectric function

De electric field component of an electromagnetic wave that is traveling in the $x$-direction is given as $$E(x,t) = E_0 e^{i(kx - \omega t)} $$ with $E_0$ the amplitude and $k$ the wave vector. From ...
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0answers
23 views

Semi infinite parallel conductors [on hold]

Semi infinite parallel conductors separated by a distance of 0.5 m are at the endpoints associated with the resistance R = 4, while according to the two without friction slides bar by weight: 0.1 kg ...
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0answers
37 views

The approximation of the potential field of a half wave dipole antenna

I'm currently deriving an approximation of the potential field of an dipole antenna in the far-field in two dimensions, and I have some troubles. Since using two methods give two different answers. ...
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1answer
41 views

Influence of spacetime curvature on electromagnetic wave propagation [duplicate]

Classical physics assumes that spacetime is evenly distributed in the sense that Coulomb's Law predicts that a charged particle will create a spherically symmetric electric field around its location. ...
2
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0answers
35 views

Holding magnet near CRT monitor damages the screen?

Few days ago I tried keeping my magnet in front of my CRT monitor screen and it was showing some cool effects like showing so many different color but then when I removed it ,that blurr effect was ...
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0answers
20 views

Amplitude of electric field produced by satellite dish [on hold]

A telecommunications satellite is in geostationary orbit and it has a 1 m transmitting dish optimised for coverage of Europe. If the output power from this dish is 100 W, very roughly estimate the ...
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0answers
13 views

Calculating work needed to move a charge between plates of an uncharged capacitor [closed]

My first guess was zero work because there's no electric field(I think). E.g. a parallel-plate capacitor $4.9 cm$ on a side, spaced $1.0mm$. The work needed to move $6.8\mu C$ seems to be $1.1J$ And ...
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What does it mean for $\vec E \in C^3$ [closed]

What is this $C^3$ and why is $\vec E$ an element of C^3?