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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How to show that the force and velocity are perpendicular and that both have constant magnitude? [on hold]

The force acting on a moving charged particle in a magnetic field $\hat{B}$ is $\hat{F}=q\left(\hat{v}\times \hat{B}\right)$ where $q$ is the electric charge of the particle, and $\hat{v}$ is its ...
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1answer
32 views

Energy Imparted by a Magnetic Field

My question is probably a bit low-brow for this forum, but here goes. As I understand it, when you switch on an electromagnet it generates a magnetic field which pervades all space, imparting ...
3
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1answer
39 views

Reflection of two electromagnetic waves

Can Electromagnetic waves be reflected by another electromagnetic wave without having any physical (transparent or opaque) material (i.e., in free space with one wave having twice the amplitude of the ...
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2answers
32 views

Why do we multiply the magnetic flux by the winding number?

A current I flows through a solenoid (with n turns). Self inductance is $L$. If the magnetic flux is $\phi$, I am taught that $-n\phi=LI$ I dont understand the part with $n$, why do we have multiply ...
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1answer
33 views

AC wire radiation

I'm trying to test my recently installed MEEP program for a very simple AC current. I know that for DC current, Ampere's law dictates that the magnetic fields must drop off as 1/r. How does this ...
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0answers
27 views

Is there transversal current inside real conductor in transmission line? [on hold]

At first, consider transmission line with two conductors where TEM mode is established and conductors are perfect. As we know, on surface of conductors we will have surface currents (connected to ...
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1answer
37 views

Really quick question about the order of operations in the Lorentz force

I'm trying to calculate the Lorentz force for a particle in a uniform electric Field, E and magnetic field B. The formulas is $$F=q(E+v\times B)$$ I'm just wondering what the order of operations is ...
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0answers
24 views

Magnetic field of magnetic screwdriver?

I wanted to know what is the typical strength of the magnetic field generated by the tip of a magnetic screwdriver, but couldn't find it anywhere on the manufacturers' webpages. So I was wondering, ...
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1answer
106 views

If protons and electrons had similar masses

If electrons and protons had the same mass, would they still be in a stable orbit around their barycenter, or would they eventually collide? Similarly, a positronium(or protonium) only lasts extremely ...
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1answer
63 views

How does EM radition depend on the reference frame?

In special relativity, magnetism is electrostatics in a different reference frame. This is how we explain the magnetic field being produced by moving charges (aka currents). Charges that move produce ...
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1answer
25 views

Direction of Induced Electric Field in a coaxial cable?

I was working through Griffith's book when I came across this problem: An alternating current, of the form $I(t) = I_0cos(\omega t) $ flows down a long straight wire, and returns (loops back) along a ...
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1answer
28 views

Potential energy given to an electron in a time-varying electric field

Given a general electric field $\epsilon(t) $ directed in the z direction, how would we calculate the potential energy given to an electron as a result of this field?
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1answer
29 views

What happens when I reverse an electrical generator?

I am trying to find out whether I could run a generator in reverse as well as forward. It will be a wind generator converted to run from a different power source. This is a new invention to which I ...
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0answers
22 views

Fusion plasma compression with liquid metal

General Fusion plans to use an imploding shockwave of molten lead to compress a magnetized plasma "spheromak" target in order to make it burn more efficiently. How come the lead does not quench the ...
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1answer
20 views

What are poles of a circular loop carrying current?

Why are the poles located where they are? How is an electromagnet formed? How can I determine the poles of an electromagnet? I'm confused about the polarity of a circular loop carrying current.
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1answer
24 views

The magnetic fields produced around a conductor carrying current are circular shaped [on hold]

So what are the north poles and south poles of this conductor?...The magnetic lines are not entering or leaving from anywhere?
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3answers
35 views

Is a flow of ionized water an electric current?

If $H_2O$ ions have a net electric charge and electric current is the flow of electric charge, can a stream of water ions be considered an electric current? If so, is it conceivably possible (not ...
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1answer
33 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 ...
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0answers
42 views

Lorentz transformations an EM fields

When deriving the Lorentz transformation equations in undergraduate physics classes, teachers typically analyze the behavior of an ideal clock and a rigid bar. Once the behavior of clocks and rods is ...
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0answers
6 views

Aluminum magnetic moment in ZnO

I have made a density functional theory on calculation zno 2x2x2 super cell and I have substituted one of the Zn atoms with Aluminum and did spin polarized calculation. I expected that the unpaired ...
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0answers
22 views

Calculating Oscillations of a small magnetic needle [on hold]

In a problem from a past physics competition paper, a wire, carrying a constant current i, forms a "V" shape (as shown below). Part four of the question states In order to measure the magnetic ...
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1answer
24 views

Magnet arcs assemly

Is it possible to join multiple Neodymium magnet arcs (shown blow), which are radially magnetized, to create a cylindrical ring unity that is also radially magnetized? If it is not possible, how to ...
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0answers
8 views

Near field and Nuclear magnetic resonance (NMR)

Why does Nuclear Magnetic Resonance (NMR) physics not concern itself with near field physics? All resonance wavelengths in NMR are much larger than bough sample, pick-up coil and excitation coil. ...
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1answer
48 views

Relationship between polarization density and electric field

Imagine I have an electric field $E$ created due to some free charges. Then I introduce a dielectric material somewhere. What confuses me is the polarization field $P$, which is now proportional to ...
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4answers
132 views

What is divergence?

What is divergence? I was learning about Maxwells equations and don't understand the divergence part of it. Can someone give an intuition of what divergence is in relation to maxwells equation. To ...
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0answers
26 views

What is DX technology and what are the effects on digital cameras?

I am photographing in a high power voltage field in Industry producing aluminium, called DX technology. How do I know if my digital camera will not be affected? At 350kA current my film cameras were ...
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0answers
15 views

Two conductor's in a magnetic field, canceling each other's EMF?

If two conductor's are in a $\Delta$B, oriented the same in the field, and they induce equal $\epsilon$, can their wiring be oriented in a way that they can cancel each other's induced $\epsilon$? So ...
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29 views

Help finding the net electric charge flux! [on hold]

If electric charge flows with a current density vector function of $$ \mathbf J=\frac7R\hat{R}\,\,\,\,\,{[\rm A\,m^{-2}]} $$ find the net electric charge flux (i.e., the net current) flowing through ...
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1answer
82 views

Is the Wikipedia article on the Kramers-Kronig relations correct?

Reading the "Physical interpretation and alternate form" section of the Wikipedia article on the Kramers-Kronig relations, it says: The imaginary part of a response function describes how a system ...
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2answers
161 views

Is manufacturing roughness really the only reason we don't see optical interference in thick dielectrics like windows?

I had always kind of wondered why we didn't see interference in things like windows -- we were taught that the condition is that the thickness of the film/slab/medium just has to be an integral number ...
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1answer
52 views

Can we double the electric energy?

If I have $x$ amount of electrical energy and convert that into mechanical energy using an AC Motor, and then convert that energy back into electric using an AC generator, will the amount of energy ...
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0answers
29 views

Why are there only 2 types of charges? [duplicate]

Why is there only 2 possible types of charges positive and negative? Can there be more, the same way there might be more than 3 spatial dimensions?
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0answers
23 views

Electric field of Symmetric Parts [closed]

So I'm preparing for a test and one thing that I haven't seen examples of, but know is possible is using Gauss's Law on objects that have symmetric parts. I made up the following question: Find ...
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1answer
36 views

Photons, electomagnetism

I read that photons are carriers of the electromagnetic force (one of the four fundamental forces). So, I would like to know what a photon has to do with, for example, working of a motor or ...
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0answers
39 views

Electromagnetism in Different Inertial Reference Frames?

Sharon drives her rocket through the magnetic field (shown in the image), travelling to the right at a speed of 1000m/s as measured by Bill. As she passes Bill, she shoots a positive charge backward ...
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2answers
115 views

Why is Curl of Current Density $\nabla \times \vec{J}$ equal zero?

I am revisiting the derivation for $\nabla \cdot \vec{B} = 0$ in magnetostatics for the field $\vec{B}(\vec{r})$ of a charge $q$ at position $\vec{0}$ with velocity $\vec{v}$. It proceeds like ...
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2answers
73 views

This electromagnetic wave diagram doesn't make sense to me

I am attempting to learn about electromagnetic waves. From my understanding, when two particles are a distance away from eachother, and one vibrates up and down, the stationary particle will ...
0
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0answers
15 views

Can we build an ideal hexadecapole? [duplicate]

I'm just curious about whether it is possible to build an ideal hexadecapole (16-pole) from point charges in 3D. My intuition tells me no, because the point charge of a (electric) monopole "bound" a ...
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0answers
26 views

How does grounding work in details

How does grounding work exactly? Let's assume there is a wire with bad insulation and some conductor that is attached to this wire (from one end) and unattached on the other end. Current will not ...
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1answer
42 views
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0answers
15 views

Induced emf of a wire in a time varying magnetic field

I have recently studied that there are two types of induced emf: motional and static. However, I was told that the that induced static emf due to a non conducting wire/rod in a time varying magnetic ...
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0answers
18 views

Question on electromagnetic wave propagation [closed]

how to do part d of this question? i have done part 1 to three but part d is bit confusing.
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0answers
122 views

The motion of the magnetic bob

I have two simplified mathematical models which should describe the motion of a magnetic bob, but there is a minimal deviation. model A (RED): use of conservative force: $V= V_M + V_G = ...
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0answers
54 views

Hamiltonian for Electron in Magnetic Field with Symmetric Gauge in Polar Coordinates

I am new on the board and have a question about how to write the Hamiltonian for an electron in a magnetic field rotating at a fixed radius. I would like to write the hamiltonian using the symmetric ...
0
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1answer
62 views

Using Cosine Law to Find Net Electric Force on Charge Always Results in Positive Number?

In order to determine the net force other charges have on a particular charge, you must take into account each individual electric force between the charge and the charge of interest. However some of ...
4
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3answers
166 views

Is it possible to prove conventional current is always equivalent to actual current?

I understand how the conventional current is logically equivalent to the actual current of electrons in a circuit. However, whenever I'm studying some new concept, and things are assumed as working ...
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3answers
48 views

Finding charge density from from differential form of gauss law

I didnt get why he didvided and multiplied by r^2.This question is from d j griffith .
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3answers
63 views

Why monopole does not radiate energy in electodynamics?

Why there is no monopole radiation in Electromagnetic field? I read somewhere that it is impossible because it violates charge conservation. I don't understand how? How charge conservation gets ...
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3answers
51 views

Potential due to a continuous charge distribution on ring

Derive the formula for the potential at point $P(0,0,z)$ directly above the center of a ring of charge with radius $R$ and uniform charge density $\lambda$. My attempt: Since $$\lambda= ...
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0answers
17 views

Effective magnetic moment

How can one calculate effect moment from susceptibility (SI*10^6) versus temperature (K) graph? What is the typical range of effect moment for ferromagnets?