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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Right Hand Rule for Proton Magnetic Field

I thought that right hand rule was for find the magnetic field generated by a current, where your thumb point in direction of the current. However, I was watching something that said we can curl our ...
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1answer
178 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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2answers
56 views

Is the electron magnetic moment responsible for the Lorentz force?

My question about the sum of the electrons' magnetic moments in a wire(What is the sum of the electrons' magnetic moments in a wire?) had an answer which disappeared later. The answer was - if I ...
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1answer
33 views

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
33 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 ...
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1answer
122 views

Understanding fields and their correlation to forces

I seem to be confused between the concept of a "force", and a field. Now let's assume there is a magnetic field of $1$ $\mathrm{Tesla}$, what does that mean in relation to force? Finally, if field is ...
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1answer
318 views

If we have a current $I$ flowing down a wire, why must the net bound current be zero?

Say we are dealing with a wire that has a current $I$ flowing through it, i.e. $I$ is the free current. Why must it then hold that the net bound current, that is, the bound volume current, $J_b$, and ...
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2answers
204 views

AC Electromagnets

Could someone help explain the uses of AC electromagnets. Wherever I look it says that DC electromagnets create stronger magnetic fields. I understand why AC electromagnets could be used in ...
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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
146 views

Is every electromagnetic radiation considered “light”?

Somebody mentioned on Freenode chatroom for physics that All Electromagnetic Radiation are delivered in form of Photons not just light. Is it true? Does that mean if we get a THF electrical ...
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1answer
144 views

Why is the magnetic field stronger at the edges of a bar magnet?

I have been performing an experiment at school in which I test the force on an iron surface from the magnetic field of an electromagnet. The electromagnet has a rectangular iron core. The theory ...
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1answer
34 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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2answers
105 views

Principle of locality and forces

I have a silly confusion about the statement written in the link Einstein and Locality ''external influence on A has no direct influence on B; this is known as the Principle of Local Action.'' ...
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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
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
116 views

Calculating the magnetic field from rectangular conductor?

I want to apply the Biot-Savart law to calculate the magnetic field at a point created by current flowing through a square/rectangular conductor. More specifically, a trace on a printed circuit board. ...
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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
366 views

Recovering all of Maxwell's equations from the variational principle

Whether you can get the first couple of Maxwell equations from a variational principle? In the second volume of the Landau theoretical physics said that it is impossible.
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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
60 views

Back EMF & Current, how can we make I stable?

Lets assume we have a wire that has $10V$ across and $1$ $Amp$ flowing, now if this conductor is introduced to a changing magnetic field, $-EMF$ is induced, can we control our voltage to increase it ...
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2answers
86 views

Determining the minimum pull force of a magnet required to hold it in place

If I place a magnet on the underside of a metal object so that it is held there by its attraction to the metal, how can I determine the minimum pull force the magnet needs to have in order to keep it ...
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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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5answers
583 views

How does a spinning electron produce a magnetic field?

I learned in my undergraduate physics class that atoms have magnetic fields produced by the orbit of electrons and the spin of electrons. I understand how an orbit can induce a magnetic field because ...
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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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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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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
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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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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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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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
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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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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1answer
94 views

Electron distribution around atom when moving

I do not have much experience on this but if an atom has some electrons around nucleus and the atom itself it is moving at some speed does that affect the distribution of electrons around? I am ...
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6answers
425 views

Are metals more heavy due to the Earth's magnetic field?

Non-metal objects are attracted to the Earth due to gravity. So the weight of non-metal objects can be only dependent on their mass. On the other hand metals can be attracted to the Earth's magnetic ...
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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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4answers
133 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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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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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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1answer
102 views

How to compute speed without knowing mass or charge values?

A gold nucleus is $460$ fm ($1$ $fm = 10^{(-15)} m$) from a proton, which initially is at rest. When the proton is released, it speeds away because of the repulsion that it experiences due to the ...
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2answers
115 views

Why does a magnetic field raise the ground state energy of an electrical particle?

I heard a statement that the ground state energy of a electrical particle in a magnetic field is larger than its ground state energy without the magnetic field. I just heard this statement. This ...
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0answers
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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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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2answers
137 views

How to measure vector potential such as that of magnetic field?

If we want to measure gravitational potential energy of a body-earth system, we can simply do it by measuring the body's height from ground. How could we can measure vector potential such as that of ...
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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 ...