# Questions tagged [magnetostatics]

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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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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### 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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
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?
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### 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 ...
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. ...
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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...
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) ...
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 ...