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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2answers
39 views
Violation of Newton's 3rd law
I'm just expressing my guess.
Let two particles A and B experiences forces $F_1$ and -$F_2$ between them and let guess also there are two observer, one is stationary and other is moving with ...
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1answer
17 views
Doubt on the analysis of $RC$ circuit
I'm studying $RC$ circuits and I'm in doubt on how to deal with one kind of situation. Well, first when we have simply a circuit with just one resistor and one capacitor in series, or a circuit that ...
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0answers
17 views
Electric and Magnetic Field [closed]
Accelerated charges directed into regions between parallel plates with E and B fields – how are the charges deflected?
2
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1answer
16 views
Magnetic Force on a Loop and number of turns
Suppose we have a rectangular current-carrying loop with current $i$, then we know that the magnetic force on each side can be found as:
$$F=iL\times B$$
Where $L$ is the vector in the direction of ...
3
votes
1answer
87 views
Is electromagnetism a dead research field?
Are there any phenomena, we consider as electromagnetic and have no explanation for ?
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0answers
22 views
electrostatic repulsion [closed]
Consider a homogeneous ring of radius $R$ made of a thin wire of cross section $A$ with $R^2≫A$. A charge $Q_1=10\mu C$, uniformly distributed over the ring, broke it apart due to electrostatic ...
2
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2answers
42 views
What really is the Magnetic Force on a wire?
I have a doubt regarding the significance of a force on a wire. Well, first of all, I know that if I have a particle and if there are several forces acting over it, then we can compute one total force ...
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0answers
14 views
What is the “relative permeability” of Neodymium?
I am currently interested in finding a high "relative permeable" material to put into the core of a solenoid. However many sources quote Neodymium's recoil realtive permeability ($\mu_{rec}$) to be ...
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2answers
54 views
How & Why does accelerating charges radiate electromagnetic radiation?
Lets consider it case by case:
Case 1: Charge particle is at rest. It has electric field around it. No problem. That is its property.
Case 2: Charge particle started moving (its accelerating). We ...
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4answers
76 views
How does moving charges produce magnetic field?
I'm tutoring High school students. I've always taught them that:
A charged particle moving without acceleration produces electric as well as magnetic field?
It produces electric field because ...
2
votes
2answers
49 views
what sort of set up would i need to create an electro magnetic chair with no legs
I am a furniture design student therefore please keep it simple. a system strong enough to hold the avergae male of say 90 kg is this possible even....
0
votes
1answer
21 views
Doubt in problem regarding resistance a of cylinder
I've been working on some exercises and I'm in doubt if my procedure with this one is correct. We have a hollow cylinder with internal radius $r_a$, external radius $r_b$, resistivity $\rho$ and ...
1
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0answers
26 views
Induced current using a reference system bound with a moving charge
Let's suppose to have a charge moving at velocity $\textbf{v}$ and a square wire.
If I choose a reference system bound with the square wire, since the charge is moving at velocity $\textbf{v}$, in ...
1
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1answer
85 views
Why the magnetic flux is not zero?
According to Maxwell's equations the magnetic flux over a closed surface must be zero, why in this case does not happen?
Thanks for your help
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0answers
13 views
Potential E alternation
Considering a permanent magnet moving in a trajectory perpendicular to a straight wire of a given lenght, in a way that the magnet expose always the north face towards the wire, no matter the ...
3
votes
1answer
70 views
Can Earth's Magnetic Field Create Electricity?
If the earth has a magnetic field, can it, in theory, be run through a conductive metal coil to create electricity?
2
votes
3answers
79 views
Radio antennas that are much shorter than the wavelength
From my limited experience with ham radio when I was a kid, I expect transmitting and receiving antennas to have lengths that are on the same order of magnitude as the wavelength, and in fact I recall ...
4
votes
2answers
87 views
Can a current carrying loop or wire produces no magnetic field?
A current carrying wire produces magnetic field around it. We can find the direction by Fleming's Right hand rule. We know change in electric filed produces magnetic field and change on magnetic field ...
5
votes
2answers
128 views
Why isn't data lost when sent over large distances?
I was thinking about how information is sent, for example through the atmosphere. There are plenty of obstacles, as well diffraction, etc.
Still, no information is lost. How is information sent to ...
0
votes
2answers
105 views
What is a “gravitational cell”?
I am not a physicist, and I don't understand the details of electromagnetism. Anyhow, I was looking for how the batteries work in Google. So, I came across this article: "How batteries work: A ...
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0answers
34 views
Magnetic Field on a particle between two Helmholtz Coils
Given a Helmholtz coil of radius $R$ and with a current $I$, and assuming the coil is a circle centered at the origin in the $xy$-plane, what is the magnetic field on a particle at the point $(a, b, ...
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0answers
78 views
Easy question about magnetism?
I have to build a simple electric motor by attaching a magnet to a battery, extending the terminals of the battery (with stiff wires so they could act as supports), and placing a coil of wire on top ...
1
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0answers
27 views
Power transfer in a transformer
Can it be proved using the concept of induced emf that power supplied at the primary coil equals power consumed at the secondary. I tried following. Let primary coil be called 1 and secondary be ...
5
votes
3answers
83 views
What causes the permittivity and permeability of vacuum?
When light travels through a material, it gets "slowed down" (at least its net speed decreases). The atoms in the material "disturb" the light in some way which causes it to make stops on its path. ...
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2answers
96 views
Derivation of the Biot-Savart Law
Can someone provide a derivation of the Biot-Savart law for electromagnetic induction? To be clear,
$$
d\vec{B}~=~\frac{\mu_0}{4\pi}\frac{I d\vec{\ell}\times \vec{r}}{r^3}.
$$
Is there a simple way ...
3
votes
3answers
165 views
Energy conserved… or not? Confused!
I am confused. Could someone kindly explain what's going on in this question?
A particle of mass $m$ and charge $e$ moves in the $x,y-$ plane. There is a constant magnetic field $B$ that points in ...
2
votes
1answer
101 views
How Special Relativity causes magnetism
So my physics teacher assigned us an article about how special relativity causes magnetism in a wire with a current, even with the low drift velocities of electrons in a current.
It seemed that the ...
1
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1answer
26 views
Capacitance of a conducting disk
I'm reading this(PDF) derivation of the capacitance of a thin conducting disk. The surface charge density of such a disk can be shown to be:
$\sigma(r) = \frac{Q}{4\pi a\sqrt{a^2 - r^2}}$ (in ...
2
votes
1answer
32 views
Falling through the ground [duplicate]
I do not know much about physics but I know that according to Newtons third law of motion when we walk we are pushing the ground down but the ground is pushing us up. What force is making the ground ...
2
votes
1answer
70 views
Trying to understand EM wave and photon
When electrical fields and magnetic fields couple together, it forms electromagnetic waves. And we can "quantized" it and see each "package" of it as photon. So can electrical fields and magnetic ...
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0answers
35 views
Magnetic Field Lines predict? [closed]
Question: Magnetic field lines determine:
(A) only the direction of the field
(B) the relative strength of the field
(C) both the relative strength and the detection of the field
(D) only the ...
0
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0answers
44 views
Is this picture of the electron dipole moment correct?
It's the electron spinning on its axis, and a magnetic moment shoots up. The direction of the North-South is opposite what I thought it should be. Why is the vector arrow pointing from North to ...
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2answers
37 views
MRI's and Electromagnetic Radiation
If the waves in an MRI can go through our body, why is it that light with its magnetic fields gets stopped at our skin?
3
votes
1answer
37 views
Charge inside conductor
I know that the E field inside a conductor is zero. What happens if I put a source of charge inside the conductor?
Say the conductor was spherical centered on the origin and there exists a charge at ...
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2answers
53 views
intensity of electromagnetic waves
I have a trouble understanding intensity of electromagnetic waves,
I already looked at this article and this question but didn't understand completely
$Intensity = \frac{\epsilon_0}{2} |\vec ...
0
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2answers
41 views
Do black holes have charges?
Do black holes have charges? If so, how would they be measured? Also, does electricity behave the same way? Black holes affect photons, which are carriers of EM radiation, so do black holes have any ...
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2answers
169 views
Ferromagnetism with mobile spins
How can electron spins in Iron at room temperature have ferromagnetic order even though they are travelling at very high speeds?
One could argue that spin and motion are completely uncorrelated and ...
3
votes
1answer
60 views
What are the limits of applicability of Coulomb's Law?
Coulomb's law is formally parallel to Newton's Law of Universal Gravitation, which is known to give way to General Relativity for very large masses. Does Coulomb's Law have any similar limits of ...
2
votes
4answers
84 views
Displacement Current - How to think of it?
What is a good way to think of the displacement current? Maxwell imagined it as being movements in the aether, small changed of electric field producing magnetic field. I don't even understand that ...
1
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1answer
76 views
Maxwell's Equations-Relativity
How did Maxwell develop the magnetic field without relativity? Was it purely experimental? I don't see how else he would have developed any understanding for the magnetic field.
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2answers
89 views
Simple ohms law on a battery ? Paradox or conceptual error?
Suppose we have a regular pencil battery which supplies DC voltage $V$. Say we take copper wire and connect the ends of the battery to an $R$ ohms resistance.
Then Ohm's law tells use the current in ...
1
vote
1answer
50 views
Magnetic induction outside of the finite length solenoid
I'm programing simulation software for solenoid and hemholtz coils, where I have to calculate B(x,y,z). I have found dozens of variations of Biot-savart law for determining B on axis. But how about ...
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0answers
15 views
Row of pivoted magnets and energy scale
This question is about a system involving a horizontal row of length L of equally spaced pivotable magnets, each with a pole at either end. These magnets will often be referred to as units.
So each ...
1
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1answer
79 views
Retrieving Maxwell's equations from the minimum action principle
I'm currently working at the start of Alexei Tsvelik's book Quantum Field Theory in Condensed Matter Physics. I'm kinda stumped on a few essential steps.
Starting with the action:
$$S = \int dt \int ...
2
votes
1answer
68 views
iPhone compass not being affected by current
As you probably know, electrical current and magnetic fields are close friends.
In an iPhone there is a compass, however there are also lots of cables and in all of them, or at least in most of them ...
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0answers
34 views
Lagrangian of electromagnetic tensor in light cone coordinates? [closed]
I have Lagrangian Density of Electromagnetic field Tensor in light cone coordinates using D'Alembertian operator and Lagrangian density in Cartesian coordinates. I couldn't figure out the way to ...
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0answers
36 views
What do I need to read so I understand these topics
I'm reading this paper.
I don't quite understand the implications of the plots in Fig. 2:
Current vs. Potential (Cyclic voltammetry)
Potential vs. Time (charge/discharge curve)
Stack capacitance ...
1
vote
1answer
30 views
A simple electromotor?
I have to build a simple electromotor in the following way: I attach a permanent magnet to a battery, connect some metal supports to the terminals of the battery, and place a coil of wire on the ...
1
vote
1answer
70 views
Ginzburg-Landau model for superconductivity
Could someone kindly elaborate more on the Simple Interpretation section from this Wikipedia Article? I refer to the part on the natures of $\alpha , \beta$. Why can one assume that ...
1
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0answers
42 views
Solving the equation of relativistic motion
How does one solve the tensor differential equation for the relativistic motion of a partilcle of charge $e$ and mass $m$, with 4-momentum $p^a$ and electromagnetic field tensor $F_{ab}$ of a constant ...
