Questions tagged [magnetostatics]

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12
votes
3answers
583 views

Magnetic scalar potential far above a magnetic film

The situation I am looking at is a magneto-static problem of a finite magnetic film with magnetization $\bf{M}$. I would like to find the the magnetic field far above the plate. My expectation is that ...
6
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0answers
129 views

Total current for an arbitrary current density

Imagine a localized region $\mathcal{R}$ which contains a current density $\mathbf{j}$, which we take to be divergence-less, $\mathbf{\nabla\cdot j} = 0$. What is the total current associated with ...
3
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1answer
74 views

How is it possible that one face of my electromagnet produces stronger magnetic field than the other?

I work in an experimental research lab. I made an electromagnet by having the machine shop cut through a toroid core and hand-winding wire around it. The objective is to have a region of uniform ...
3
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0answers
1k views

Force between two current carrying wires: the general case

Assume two straight current carrying parallel wires with currents ($I$ and $I'$) flowing in the same direction, at a distance $R$ from each other. From Ampère's law (and from Biot-Savart as well) it ...
3
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0answers
231 views

Where can I find actual data for the hysteresis of a magnetic material?

When a magnet is exposed to an external magnetic field it can be further magnetized or demagnetized. This amount can be found by looking at the hysteresis curve for that magnet. I do not have the ...
2
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1answer
52 views

Magnet modeling

I wrote simple physics mass-spring engine, and I want to add the magnetism. Each body consists of tiny connected spheres with some mass. The only input values to calculate magnetic interactions I ...
2
votes
1answer
89 views

An absurd consequence of magnetic field as an axial vector

One of the definitions of magnetic field (in free space): Force on magnetic north pole per unit pole. Magnetic field is an axial vector. So it changes its sign when we use left handed coordinate ...
2
votes
1answer
64 views

Can I replace a multipole expansion by a combination of separate dipoles?

If I want to be able to model a magnetic field flux density $\mathbf{B}$ from a magnetic source located at the origin at a position $\mathbf{r}$, it is my understanding that I can represent $\mathbf{B}...
2
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0answers
178 views

Diamagnetic materials with negative susceptibility?

I have been learning about magnetostatics, and from reading about the existence of diamagnetic, paramagnetic and ferromagnetic materials I was under the impression that a limiting value for magnetic ...
2
votes
2answers
375 views

Find torque due to Lorentz force - Wrong result

Current I is coming from the Z axis and then it flows out uniformly towards the circumference of this disk. The disk has thickness t and Radius R. There is also a constant B field in the Z direction(...
2
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0answers
301 views

When do we have a coherent magnetization rotation? (single-domain particles)

So I am studying micromagnetics + spintronics and I am little bit confused with certain concepts regarding the physics of magnetic domains (especially single domain particles): What I already knew: ...
1
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1answer
19 views

Magnetic field inside a ferromagnetic material

Let us suppose there is a block of a ferromagnetic material inside a very long ideal solenoid. We know that the magnetic field lines inside are always in a straight line which will be perpendicular to ...
1
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0answers
40 views

Why would a ring magnet's flux decrease once distance starts getting small?

I went ahead and use python magpylib to simulate a ring magnet joystick, and then graph flux over distance of the ring magnet. Here's the code: ...
1
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0answers
28 views

Guoy method derivation, or, how not to break math?

I start from $d\vec{F}=\nabla(\vec{m}\vec{B})$, $\vec{M}=\frac{d\vec{m_i}}{dV}$, and $\vec{M}=\frac{\chi_v}{\mu_o}\vec{B}$. I write out the definition of the force, determine we're only interested ...
1
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0answers
58 views

Solving the Line Integral in Ampère's Law mathematical correctly

Imagen we have a infinite long, cylindrical conductor with radius $\varrho_0$ and $\textbf{j}=\begin{cases}j_0 \textbf{e_z} &r\leq \varrho_0\\ 0 &r>\varrho_0\end{cases}$ We have Ampère's ...
1
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1answer
52 views

How is the third case obeying integral form of Maxwell's second equation?

Let $m$ denote pole strength. In the diagrams: (1) Sky blue: Closed Gaussian surface (2) Red: North pole of magnet (3) Green: South pole of magnet (4) Yellow: Part of magnet cutting Gaussian surface ...
1
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0answers
70 views

How to calculate the magnetic field of two cylinders when one of them is rotating

Given is the voltage U and the Angular velocity $\omega$. The rotating cylinder is inside the other cylinder and U is measured between them. To calculate the magnetic field, I tried to solve $\oint ...
1
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1answer
58 views

Demagnetising $H$ field

If we have a permanent magnet we know that we have a $H$ field opposite in direction to the residual magnetic field $B_r$. The $H$ field causes a demagnetisation, but how does it do it? We know that ...
1
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0answers
94 views

Boundary conditions in the method of images

My question is very similar to this one. The problem: A long thin wire carrying a current $I$ lies parallel to and at a distance d from a semiinfinite slab of iron. Assuming the iron to have infinite ...
1
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0answers
606 views

Surface current density (magnetic materials)

In deriving the boundary conditions for $H$ at the boundary between two media, my lecturer stated that "since there is no conduction (free) current on the Surface... the tangential components of H are ...
1
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0answers
86 views

Force Lines of Magnetic Field of Circle Loop

Magnetic field of a loop with a stationary current in a xy plane with center in the origin is usually computed on the z axis. Out of the z axis the calculation results into elliptic integrals. I would ...
1
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0answers
203 views

Is current always constant with time in electrostatics?

In electrostatics, electric and magnetic fields are not time-variant. In that situation, I guess that current must be stationary. Otherwise, $\partial E/\partial t \ne 0$ because if it were stationary ...
1
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1answer
101 views

How does the continuity of $\bf A$ ascertain the parallel components $\boldsymbol\nabla(A_{i,1}-A_{i,2})$ being zero but not the normal one?

I was reading in this pdf about the discontinuity of the derivative of the vector potential $\mathbf A$ across a boundary with $\hat{\mathbf n}$ acting as the normal to the plane having surface ...
1
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0answers
62 views

Would setting a magnetic base to the “off” position remove the torque from an external field?

A magnetic base is a permanent magnet mostly inside a ferromagnetic case. It can be rotated so that the field is either internally shunted through the ferromagnetic blocks, or so that the blocks are ...
1
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0answers
31 views

Do you know if you have zerovalent iron nanoparticles in liquid how to measure minimal magnetic force required for separation of these nanoparticles?

I think of measuring mag susceptibility from VSM data (magnetization divided by the applied field) but I am not sure if this would be enough. Maybe if I employ SQUID measurements, but in that case I ...
1
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0answers
31 views

Why do magnetic forces scale down so poorly?

Im told by experts in MEMS and nanotech that magnetic forces scale down very poorly. This is one reason we have many MEMS devices based on electric forces/electrostatics but not on magnetics. Can ...
1
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0answers
71 views

Anyone know of a flow chart or list of common/useful consequences of Maxwell's equations?

I just recently started to appreciate the Maxwell equations. I had never really take the time to study them but I feel like I'm finally more familiar with them. I've noticed that it seems like a lot ...
1
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2answers
59 views

How do magnetic shields work?

I've come across the fact that magnetizable material can shield magnetic fields. For example, if I put a ferromagnetic plate between the magnet and a nail that is hanging on a thread pulled towards ...
0
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0answers
44 views

A theory where it's convenient to express a scalar quantity as a divergence of a vector

The equations of electrostatics,$$\nabla \cdot \vec{E} = \rho, \quad \nabla \times \vec{E} = 0$$make it possible to introduce the scalar potential $\vec{E} = - \nabla \phi$, which then satisfies the ...
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0answers
36 views

Trying to derive the force on the local current distribution in the external magnetic field

I am trying to derive the formula of the force on local current distribution in an external magnetic field as shown below. Since $ \ \ \ {d \hat F=I \ d \hat L \times \hat B} \ \ $, I come up with the ...
0
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0answers
24 views

Hysteresis loop in Griffiths' Introduction to electrodynamics

In Griffiths' Introduction to electrodynamics there's the following Hysteresis Graph: Shouldn't it be $10^{-4}$ instead of $10^{4}$ on the x-axis?
0
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1answer
29 views

The amount of current needed to accelerate for specific speed

In the magnetic gun a conducting rod is placed on a two rails connected to a voltage source, so that a current can flow in the rod. Magnetic field $\vec{B}$ is applied perpendicular to the rail-rod ...
0
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1answer
36 views

Magnetic field on an arbitrary point ON a Current Loop

Consider this situation given above. We have an arbitrarily shaped theoretical current loop made up of wire of zero radius in free space. Away from all electromagnetic, gravitational interactions. ...
0
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1answer
40 views

Formula of magnetic flux through a loop as a function of time

I was studying Lenz's law and self inductance when I came across the following question. Take R to be the radius of a circular loop, which has a magnetic field perpendicular to this loop. We let the ...
0
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0answers
13 views

How to prove that magnetic flux density satisfies Ampere's Circuital Law

Here is the expression for Magnetic flux density B which derives from Magnetic vector potential A. I have trouble proving that B in this equation satisfies the differential form of Ampere's Circuital ...
0
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0answers
61 views

How do you prove $\int (x^ij^k+ x^kj^i)\,\mathrm d V =0$?

I have got a problem when trying to calculate the second term of the expansion of the vector potential $\boldsymbol A$. My textbook gives me a formula yet without proof. The problem is to prove $$ \...
0
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0answers
50 views

Compute permanent magnet movement in magnetic field

Assume I have tiny magnet particles in vacuum, which are not considered as a points, although they are very tiny. Magnet particles are situated in a uniform magnetic field. How can I can describe the ...
0
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0answers
69 views

Magnetic field through ferromagnetic cylinder when length is much bigger than the radius?

To preface, this is indeed a homework problem. I am a mathematician taking an electromagnetism module and have trouble wrapping my head around the problem at hand, and am struggling to start a ...
0
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0answers
22 views

magnetostatics and electrostatics orbiting an object with a field

I understand from the Feynman notes on physics how a static magnetic field in one frame of reference becomes a static electric field in a reference frame in which I move at the same speed as the drift ...
0
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0answers
30 views

How do I prove that the integral of a dot product of position vector and current distribution over all space is zero?

I am currently taking intro electrodynamics. My professor showed us that the for a current distribution $\vec{j}(\vec{r})$, the following relation is true: $\int d^{3}r' j_{k}(\vec{r}') = 0$ And I ...
0
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0answers
108 views

Permittivity and electric Susceptibility intuition

I have a question on the intuition behing the relation between relative permittivity $\epsilon(\omega)$ and electric susceptibility, $\chi_e$ of a of a material, more precise a dielectric medium. ...
0
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0answers
52 views

Deriving the formula for the magnetic field of a Helmholtz coil by using cylindrical coordinates

I have following problem: I want to calculate the magnetic field inside a Helmholtz coil but instead of using Cartesian coordinates I want use Cylindrical coordinates. My approach: The Biot-Savart ...
0
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3answers
41 views

Magnetic force on current carrying wire

when we keep two wires near each other then they will experience same force is it then correct to explain by newton's 3rd law? -
0
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1answer
126 views

How to use Ampere's law for a semi-infinite current sheet?

I have a very thin current sheet with constant current density K in the y-direction, length w in the x-direction, and infinitely long in the y-direction. I have to find an expressions for the magnetic ...
0
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0answers
40 views

Doubt on why magnetic flux density is solenoidal

The $\mathbf{H}$ field can be derived from the potential $\psi$: $$\mathbf{H}=\dfrac{\mu_0}{4 \pi} \int_{V'} \rho \dfrac{\mathbf{r}-\mathbf{r'}}{|\mathbf{r}-\mathbf{r'}|^3} dV' + \dfrac{\mu_0}{4 \pi}...
0
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1answer
42 views

Confusion regarding torque given by M×B

The magnetic torque acting on a loop of magnetic moment M placed in a magnetic field B, is given by τ=M×B. My question is, about which axis does this give the torque about? Is it the instantaneous ...
0
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0answers
21 views

Similarities and analogies between the $E, P$ and $D$ fields with the $B, M$ and $H$ fields and their limitations

In the course of my learning electromagnetism, I’ve noticed there are a striking amount of symmetries in electrostatics and magnetostatics, almost down to replacing divergence operators with curl ...
0
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1answer
107 views

Curl of magnetic field produced by current carrying wires with infinitesimal small area

Can Magnetic fields produced by thin current carrying wires with infinitesimal area have curl with a delta function in it ?? As area is Zero current density J definitely becomes infinite at where ...
0
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0answers
38 views

Two ways, different result: Find torque due to magnetic force on a conductor

We have an AB conductor of length $2L$ and an infinite one coming out of the screen as shown in the picture (a is the distance between the 2nd conductor and the middle of the finite conductor) ...
0
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0answers
80 views

Net magnetic field & magnetization on a ferromagnetic material

A ferromagnetic materiel is saturated by an exterior magnetic field like so: Where $B_1$ is a uniform magnetic field. Then after some time $t$ another magnetic field $B_2$ is introduced as well, but ...