Questions tagged [electromagnetism]
The classical theory of electric and magnetic fields, both in the static and dynamic case. It also covers general questions about magnets, electric attraction/repulsion, etc. Distinct from electrical-engineering.
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How do moving charges produce magnetic fields?
I'm tutoring high school students. I've always taught them that:
A charged particle moving without acceleration produces an electric as well as a magnetic field.
It produces an electric field ...
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Can Maxwell's equations be derived from Coulomb's Law and Special Relativity?
As an exercise I sat down and derived the magnetic field produced by moving charges for a few contrived situations. I started out with Coulomb's Law and Special Relativity. For example, I derived the ...
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Does the $\frac{4}{3}$ problem of classical electromagnetism remain in quantum mechanics?
In Volume II Chapter $28$ of the Feymann Lectures on Physics, Feynman discusses the infamous $\frac43$ problem of classical electromagnetism. Suppose you have a charged particle of radius $a$ and ...
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How can I stand on the ground? EM or/and Pauli?
There is this famous example about the order difference between gravitational force and EM force. All the gravitational force of Earth is just countered by the electromagnetic force between the ...
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How and why do accelerating charges radiate electromagnetic radiation?
Let's consider it case by case:
Case 1: Charged particle is at rest. It has an electric field around it. No problem. That is its property.
Case 2: Charged particle started moving (it's accelerating)....
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Can tin foil hats block anything?
This is joked about all the time, but...
Can tin foil hats actually block anything? If they can, what frequencies? Is there any research into tin or aluminum foil and radio blocking or amplifying ...
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How can magnets be used to pick up pieces of metal when the force from a magnetic field does no work?
I learned that the force from a magnetic field does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how ...
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Do Maxwell's Equations overdetermine the electric and magnetic fields?
Maxwell's equations specify two vector and two scalar (differential) equations. That implies 8 components in the equations. But between vector fields $\vec{E}=(E_x,E_y,E_z)$ and $\vec{B}=(B_x,B_y,B_z)$...
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If you are vacuuming your carpet and you wrap the cord around your body do you become a magnet?
If you wrap an active electric cord around your body, do you become an electromagnet?
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What is the mechanism behind the slowdown of light/photons in a transparent medium?
So light travels slower in glass (for example) than in a vacuum. What causes light to slow down? Or: How does it slow down? If light passes through the medium, is it not essentially traveling in the "...
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How exactly is a normal force exerted, at the molecular level?
I've been surfing the web for quite a while, finding the answers I would need, but couldn't find a convincing one. First of all I need to remind you that this a very long/continuous question, so ...
user226894
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If like charges repel, why doesn't a charge break itself apart?
How can it be that, if like charges repel, they don't repel themselves? In other words, why don't charges break apart?
About the possible duplicate: I want to know about charges in general, not just ...
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Why don't the Earth's oceans generate a magnetic field?
Many questions have been asked here about why the Earth has a magnetic field, e.g.,
What is the source of Earth's magnetic field?
How does Earth's interior dynamo work?
How can an ...
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What's the physical meaning of the statement that "photons don't have positions"?
It's been mentioned elsewhere on this site that one cannot define a position operator for the one-photon sector of the quantized electromagnetic field, if one requires the position operator have ...
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Does electricity flow on the surface of a wire or in the interior?
I was having a conversation with my father and father-in-law, both of whom are in electric related work, and we came to a point where none of us knew how to proceed. I was under the impression that ...
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What is the difference between the magnetic $H$-field and $B$-field?
From Wikipedia:
"The term (Magnetic Field) is used for two distinct but closely related fields denoted by the symbols $B$ and $H$, where $H$ is measured in units of amperes per meter in the SI. $...
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What equation describes the wavefunction of a single photon?
The Schrödinger equation describes the quantum mechanics of a single massive non-relativistic particle. The Dirac equation governs a single massive relativistic spin-½ particle. The photon is a ...
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Does a constantly accelerating charged particle emit EM radiation or not?
The Abraham-Lorentz force gives the recoil force, $\mathbf{F_{rad}}$, back on a charged particle $q$ when it emits electromagnetic radiation. It is given by:
$$\mathbf{F_{rad}} = \frac{q^2}{6\pi \...
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How wrong are the classical Maxwell's equations (as compared to QED)?
Now, I don't really mean to say that Maxwell's equations are wrong. I know Maxwell's equations are very accurate when it comes to predicting physical phenomena, but going through high school and now ...
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Is Biot-Savart law obtained empirically or can it be derived?
There's already a question like this here so that my question could be considered duplicate, but I'll try to make my point clear that this is a different question.
Is there a way to derive Biot-...
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Intuitively, why does putting capacitors in series decrease the equivalent capacitance?
Can someone please explain, intuitively (without any formula, I understand the formulas), why the equivalent capacitance of capacitors in series is less than the any individual capacitor's capacitance?...
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Phase shift of 180 degrees of transversal wave on reflection from denser medium
Can anyone please provide an intuitive explanation of why phase shift of 180 degrees occurs in the Electric Field of a EM wave, when reflected from an optically denser medium?
I tried searching for ...
WhizKid
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If magnetic field lines don't exist, what are these iron filings doing around a magnet?
Obviously the iron filings can be seen aligning themselves along the virtual magnetic field lines produced by the permanent magnet, the virtual magnetic field line is made of electromagnetic field due ...
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Home experiments to derive the speed of light?
Are there any experiments I can do to derive the speed of light with only common household tools?
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Cyclist's electrical tingling under power lines
It's been happening to me for years. I finally decided to ask users who are better with "practical physics" when I was told that my experience – that I am going to describe momentarily – prove that I ...
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Is there an underlying physical reason why the Coriolis force is similar to the magnetic component of the Lorentz force?
I couldn't help but notice that the expression for the magnetic component of the Lorentz force,
$$\mathbf F = q\,\mathbf v \times \mathbf B\,,$$
is very similar in its mathematical form to the ...
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Why is there no magnetic field around a wire connected to electricity at home?
Is it true that an electric current that flows through a conductor creates a magnetic field around the conductor?
If yes, then why doesn't the magnetic sensor of my mobile device react in any way to ...
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Why do physicists believe that there exist magnetic monopoles?
One thing I've heard stated many times is that "most" or "many" physicists believe that, despite the fact that they have not been observed, there are such things as magnetic monopoles.
However, I've ...
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Why do electrons occupy the space around nuclei, and not collide with them? [duplicate]
We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the ...
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Is there an intuitive explanation for why Lorentz force is perpendicular to a particle's velocity and the magnetic field?
The Lorentz force on a charged particle is perpendicular to the particle's velocity and the magnetic field it's moving through. This is obvious from the equation:
$$ \mathbf{F} = q\mathbf{v} \times \...
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How does this "simple" electric train work?
In this YouTube video, a dry cell battery, a wound copper wire and a few magnets (see image below) are being used to create what can be described as "train". It looks fascinating but how does this ...
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In electrostatics, why the electric field inside a conductor is zero?
In electromagnetism books, such as Griffiths or the like, when they talk about the properties of conductors in case of electrostatics they say that the electric field inside a conductor is zero.
I ...
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How are magnets held together, and why do they not explode?
Imagine we have a magnet (red side is the north pole, blue side is the south pole), and imagine two ways to split it.
The first way:
When we split it by separating the north pole from the south pole, ...
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What was Feynman's "much better way of presenting the electrodynamics" -- which did **not** appear in the Feynman lectures?
Does anyone know what Feynman was referring to in this interview which appears at the beginning of The Feynman Tips on Physics? Note that he is referring to something that did not appear in the ...
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Derivation of Maxwell's equations from field tensor lagrangian
I've started reading Peskin and Schroeder on my own time, and I'm a bit confused about how to obtain Maxwell's equations from the (source-free) lagrangian density $L = -\frac{1}{4}F_{\mu\nu}F^{\mu\nu}$...
amc
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How did physicists know that there are two kind of charges?
Problems
The question I am about to make is either too stupid or hasn't bothered anyone because its obvious because I can't really find the answer anywhere.
I am currently studying electricity and ...
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Difference between spin and polarization of a photon
I understand how one associates the spin of a quantum particle, e.g. of a photon, with intrinsic angular momentum. And in electromagnetism I have always understood the polarization of an EM wave as ...
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Is the presence of a magnetic field frame-dependent?
I do not have a strong background in physics, so please refrain from using complex mathematics in any answers :)
I was on
this site, and I read:
When an electrical charge is moving or an ...
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What is the possibility of a railgun assisted orbital launch?
Basic facts: The world's deepest mine is 2.4 miles deep. Railguns can acheive a muzzle velocity of a projectile on the order of 7.5 km/s. The Earth's escape velocity is 11.2 km/s.
It seems to me ...
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Does alternating current (AC) require a complete circuit?
This popular question about "whether an AC circuit with one end grounded to Earth and the other end grounded to Mars would work (ignoring resistance/inductance of the wire)" was recently asked on the ...
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Apparent Violation of Newton's $3^{\text{rd}}$ Law and the Conservation of Momentum (and Angular Momentum) For a Pair of Charged Particles
Consider a system of the two identical positive point charges situated in free space (isolated from the influence of any other external fields) as shown in the attached diagram. Particle $1$ is at $(a,...
user87745
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Without the Michelson-Morley experiment, is there any other reason to think speed of light is the universal speed limit?
If the Michelson-Morley experiment hadn't been conducted, are there any other reasons to think, from the experimental evidence available at that time, that Einstein could think of the Special Theory ...
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Is it theoretically possible to shield gravitational fields or waves?
Electromagnetic waves can be shielded by a perfect conductor. What about gravitational fields or waves?
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Can someone please explain magnetic vs electric fields?
I've looked through about 20 different explanations, from the most basic to the most complex, and yet I still don't understand this basic concept. Perhaps someone can help me.
I don't understand the ...
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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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Why doesn't light, which travels faster than sound, produce a sonic boom?
I know that when an object exceeds the speed of sound ($340$ m/s) a sonic boom is produced.
Light which travels at $300,000,000$ m/s, much more than the speed of sound but doesn't produce a sonic ...
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Can the Lorentz force expression be derived from Maxwell's equations?
The electromagnetic force on a charge $ e $ is
$$ \vec F = e(\vec E + \vec v\times \vec B),$$
the Lorentz force. But, is this a separate assumption added to the full Maxwell's equations? (the ...
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How can any light get past a polarizer?
The sun sends out unpolarized light. There are infinite degrees in which these photons are oriented. A polarizer only lets in light of one specific orientation.
In statistics, the infinitesimal area/...
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