Questions tagged [magnetic-fields]
For questions that utilize the concept of magnetic fields (commonly denoted by the letter B), or for questions whose answers likely involve magnetic fields. More specific than the [magnetism] tag, as questions about the phenomenon & theory of magnetism do not necessarily involve the discussion of fields.
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Time-scale of demagnetization of permanent magnets due to external field
I wonder what the time scale to demagnetize a fully magnetized permanent magnet with an external magnetic field is. The temperature is assumed to be constant.
I found a reference 1 for specific cases, ...
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In what proportions is magnetic moment caused by spin and orbiting of electrons?
(What Im basically trying to understand is what causes magnetism, but this is a specific bit of that discussion)
In all discussions of this topic I hear about magnetic moment of electrons due to them ...
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What is 90 or 180 "degree" RF pulse in MRI?
I am studying MRI, specifically spin echoes.
Now I kind of understand how magnetic resonance imaging works, but what I'm stuck is the definition of "degree" in MRI. What I thought was that ...
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Energy increase due to the Zeeman effect
The Zeeman effect is the change in energy of a system with a permanent magnetic moment in the presence of an external magnetic field. Consider electrons for example. In general, in $B \neq 0$ ...
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Why the divernce of this magnetic field is not zero?
I am working on a project on which I need to calculate the geomagnetic field in different coordinates. When I use the conventional form of the dipole field in spherical coordinates:
$$\vec{B}_{r,\phi}=...
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An infinitely spinning magnet is placed at the center of a sphere filled with mercury. Will a magnetic field be generated along the system’s $z$-axis?
The magnet’s field vector is perpendicular to its spin axis, its angular velocity is as high as it can be without destroying itself or the overall system (unless a lower velocity would produce ‘better ...
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What is the flux linkage or inductance or induced voltage per unit length of the hollow tube conductor surrounding the inner conductor?
What is the flux linkage or inductance or induced voltage per unit length of the hollow tube conductor surrounding the inner conductor in some section due to the current in the inner thin conductor?
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How to calculate the magnetic field produced by an electron spin?
A circular coil carrying current has a magnetic moment associated with it and it produces magnetic field. A electron spin also has magnetic moment associated with it. Hence it should also produce ...
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Hand-wavy method to ampere's law for a single coil of wire
Based on this question
Ampere's law and Biot-Savart law gives different terms for magnetic field in middle of a current running in a loop
I made the following square Amperian loop:
where I have ...
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If I spin a magnet in a coil which has a length parallel to the magnet’s spin axis, is a magnetic field generated along the length of the coil?
This I feel is a bit of a complicated question, so I’ll quickly try to paint as clear a picture as I possibly can:
The magnet is spinning on an axis perpendicular to its poloidal axis (the line which ...
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Why do most MRI machines and fusion reactors use helium-cooled superconducting magnets instead of cheaper, higher-temperature nitrogen-cooled ones?
I am always hearing about the high (and increasing) costs of helium, as well as the difficulty of handling it....
Are there no high(ish) temperature superconductors that can create a strong enough ...
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Describing the strength of a magnetic field
There is one thing I can never get right. If I want to describe the strength of a gravitational field I can use the standard gravitational parameter ($\mu$), which does not take into account the ...
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Superposition of Magnetic Fields
Two part question:
If I have two coils of wire facing each other with all parameters for both being equal: Current, radius, # of turns, current traveling in same direction, etc. and there is a space ...
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Notations of anisotropic Gaussian type orbital basis set in cylindrical coordinate system
I can't understand notations of anisotropic Gaussian type orbital basis (formula 2 from this article: https://arxiv.org/pdf/1709.05553.pdf). Please help me figure it out.
$$\chi_j(\rho,z,\phi)=N_j\rho^...
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U-shaped magnet and the moving charge: Where is the origin of the Lorentz force from the viewpoint of the moving charge?
Assume that a charge $+q$ is located at rest between the poles of an infinitely long U-shaped magnet, which is laid along the $x$-axis. If the charge slowly accelerates to a velocity $v$ along $x$ and ...
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What is the electrical influence of a magnetic field on alternating currrent
Assume we put a very strong permanent magnet close to an AC carrying wire.
What would the electrical effects on the wire be?
Would there be any impedence or extra resistence caused?
Could a permanent ...
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Computing mutual inductance given only magnetic fields
I am experimenting with numerically computing the mutual inductance between a number of coils in the presence of various magnetic materials.
Traditionally, the mutual inductance is found by ...
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How to find optimal parameters in Gaussian basis set?
I try to replicate some results of this article - https://onlinelibrary.wiley.com/doi/abs/10.1002/pssb.2220930140
The article here: https://drive.google.com/file/d/1q74hAn0UAdNd8DtPkoCsdYPkr61-xhr2/...
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Can magnetic fields be produced in other ways besides from a moving charge?
From my understanding, a moving charge produces a magnetic field, and a non-moving charge does not produce a magnetic field. However, I'm wondering if there's a way for a magnetic field to be produced ...
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Are Superconducting deflections of asteroids possible?
Example problem:
A 1m radius deposit of Metallic H²S(Sulfur Hydride) is trapped inside of a 50km radius Asteroid weighing approximately 3.75×10¹⁷Kg; it is under constant pressure of 95GPa; it is ...
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What is the velocity in the Lorentz equation relative to when considering a vacuum?
The Lorentz Equation
$\mathbf{F}=q(\mathbf{E}+\mathbf{v} \times \mathbf{B})$
involves a velocity vector $\mathbf{v}$. What is this velocity relative to? Based on e.g. this resource, it seems that when ...
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Larmour frequency in elecron scopic resonance spectrometer
the formulla of larnour frequency is $w=(e/2m)B$, Here w is angular frequncy
but in the experimental manual of ESR is w=(e/2mc)H,here h magnetic field intentsity
the question is how the formulla is ...
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Dipolar field in terms of demag. tensor
Assuming a potential as
$$\Phi=\frac{1}{4\pi}\oint_S \frac{\vec M(\vec r')\cdot\hat n}{|\vec r - \vec r'|}da' \tag{1}\label{1}$$
where the integral can be written as
$$\int_V \nabla' \left(\frac{\vec ...
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With induced voltage, what is the electric potential difference?
Lets say we have a closed circular loop of wire in a constant magnetic field in the (-z) direction. If I suddenly make the circular loop smaller (meaning a smaller surface area), I will induce a ...
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Motor Effect Experiment
I recently saw an demonstration (image below) where the motor effect was being shown. They used the fact that forces come in pairs (Newton's third law) and so when current goes through the copper rod, ...
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Dirac string and nature of singularities
The Dirac magnetic monopole is defined as
\begin{align}
\vec{B}=\frac{g\vec{r}}{r^3}\,,
\end{align}
where $g$ is the strength of the monopole and $\vec{r}$ a vector. It is possible to show that the ...
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How to calculate the Force between a magnet & an induced dipole? [closed]
https://www.youtube.com/watch?v=xTwDZJG_W9w
In this video at 9:12 it details the potential energy of an induced dipole
Specifically
$$U=-mBcos\theta=(\frac{\chi V}{\mu_0}B)Bcos\theta$$
&
$$F_z=\...
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Is magnetic field inside a current carrying conductor uniform?
Well, this popped inside my head when I was doing Boit-Savart's law.
$$d\vec{B}=\frac{\mu_{0}I d\vec{l} \times \vec{r}}{r^3}$$
l is the vector that represents the current element (i.e the direction of ...
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What equations would I use to work out the field strengths of Helmholtz coils powered with AC?
It is relatively easy to find equations to work out the strength of the magnetic field of Helmholtz coils, usually at the centre. However the coils are often powered with DC. Although I would imagine ...
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How to determine the electric and magnetic fields from $*F=q\sin \theta d\theta \wedge d\phi$?
I have the 2-form $*F=q\sin \theta d\theta \wedge d\phi$, how can I determine the eletric and magnetic fields from that?
I have tried wrtting F in the vector potential form for them finding the ...
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What magnetic field would be created by an electric charge that oscillated in time, but not space?
I've been reading up on electric charges that oscillate in space, creating radio waves and the like, and it's got me wondering.
If an otherwise stationary spherical electric charge oscillated in time, ...
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Electromagnets and distribution of force
How do electromagnets push things? My current understanding and assumption is that in a nutshell it is like this:
All of these forces in the end in the scenario in the picture above would just have a ...
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Faraday's law: How to interpret flux on a time/voltage graph?
Background
This is related to a homework assignment, but my question is more on the conceptual side. I will therefore only paraphrase the problem.
Problem
The question begins with the idea of dropping ...
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Can we change the direction of light by electric field?
As we know light is an EM wave.
So there is a changing electric field and a changing magnetic field in perpendicular direction of the electric field, So can we use an additional electric field to ...
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Why the angle of nuclear magnetic moment of the proton with an external magnetic field is 54,7°?Why it is not completely parallel to the ext field?
When trying to understand the basics of Nuclear Magnetic Resonance I always found that the angle between the nuclear magnetic moment of the proton and the allied external magnetic field is 54,7° but I ...
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What is the magnetic effect of a spinning charge?
A changing electric field produces a magnetic field, but if the electric field is spherical, this would mean that the field strength around the electric charge would be independent of such rotation, ...
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The maximum magnetic field outside a superconductive disk located inside a uniform magnetic field
What is the (maximum) magnetic field outside a superconductive disk located in a uniform magnetic field $B$ and very close to the edges? (Consider the London penetration depth to be zero and let the ...
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Spin effects of electric and magnetic fields
If a spin-up-along-vertical particle is passed through a second magnetic field which is horizontal and asymetric (eg a horizontal stern-gerlach apparatus), and subsequently re-measured (via a third ...
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Schrodinger's equation solutions for hydrogen in a strong magnetic field
I've read that in the vicinity of a neutron star, the magnetic fields are so strong that (other environmental factors aside) conventional chemistry breaks down because orbitals/electron configurations ...
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Magnetic circuit with multiple path
Let's image we have a usual magnetic circuit consisting of an rectangular c-shaped iron core, with a coil wound on it and a small air gap on the other side.
Now let's make another two variants:
We ...
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How can flux linkage (a 3D concept) be defined for a cross section?
The authors of Power Systems Analysis calculate the inductance per unit length (henrys/meter) of a transmission line attributed only to the flux inside the conductor as "flux linkages per ampere.&...
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Does the electric field ($E$ caused by induction) of a moving conductor in a magnetic field drop when connected to a curcuit?
We know that when a conductor moves in a homogenous magnetic field that is perpendicular to itself due to the amount of electric charge gathered on one end of the conductor( as a result of the lorentz ...
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Why doesn't coil in an Ac generator not get deflected in accordance to the flemming's left hand rule when current starts to flow through it [closed]
Why doesn't coil in an Ac generator not get deflected in accordance to the Flemming's left hand rule when current starts to flow through it.
When the coil is ...
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Are Magnet Lasers Possible? [closed]
Are there any theories concerning the possibility of magnet lasers? A magnet laser would be similar to an optical laser, but instead of light it sends a ...
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Is the magnetic field related directly to the Pauli exclusion principle? [closed]
The fact that the spin is a quantity related to the magnetic field, is it a consequence of the Pauli exclusion principle or vice versa?
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What is the difference between paramagnetic and ferromagnetic?
What is the difference between paramagnetism and ferromagnetism?
Before answering, I want to note my difference between the rest of the similar questions on this website: from what I think I know, ...
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Why does magnetic force only act on moving charges?
I don't understand why the magnetic force only acts on moving charges. When I have a permanent magnet and place another magnet inside its field, they clearly act as forces onto one another with them ...
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Response of a loop of current vs. a rigidly rotating charged ring to a magnetic field
In a uniform magnetic field, a loop of current on a wire will feel a torque that makes the magnetic moment of the loop align with the field direction. But for a rigidly rotating ring of charge, its ...
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Why can we always find $\vec A$ such that it satisfies Coulomb (or Lorenz) gauge and Maxwell's equations?
I have a short question about the Coulomb potential.
Let $\vec{E}$ and $\vec{B}$ be the electric field and magnetic field respectively.
The electric field and magnetic fields are described by the ...
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Is my proof for $\vec{\nabla} \cdot \vec{B}=0$ correct?
Here, Richard Haskell proves the Lorentz force using Lorentz transformations. Equation $(92)$ mentions the formula for $\vec{B}$ as follows,
$$\vec{B}=\frac{\gamma}{c^{2}}\left(\vec{v}×\vec{E'}\right)....
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