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 [tag:magnetism], as questions about the phenomenon & theory of magnetism do not necessarily involve the discussion of ...

learn more… | top users | synonyms

4
votes
0answers
86 views

Quantum Cyclotron Frequency - Why is it off by a factor of 2?

Say you have a magnetic field $\vec{B}=(0,0,B_0)$. Then the Schrodinger Equation Hamiltonian for a spin-2 particle of charge $e$ moving in this field is: $$H = ...
3
votes
0answers
240 views

Finding the terminal velocity of a magnet dropped in a solenoid

We have to find proportionality of the terminal velocity with the factors of the system: Plot: a small dipole(mass $m$) with dipole moment $\mu$ is dropped in a long solenoid (radius $r$, ...
2
votes
0answers
37 views

Induced current created by a magnet falling in a copper tube?

One of the educational demos often shown in schools is to drop a high strength neodymium magnet down a length of copper tube. It takes a considerable time to exit the tube because as it falls it ...
2
votes
0answers
69 views

Odd experiment results (electromagnetics)

Okay, a bit of background. So I'm working on a linear accelerator (you might know it as a Gauss rifle), and I had worked through the equations I thought I needed (Magnetic force, displacement, etc.) ...
2
votes
0answers
69 views

Magnetic Force on a Ferromagenetic Material

I am currently working on a project involving solenoids, and I needed a force(Newtons, not a measure of magnetic field strength) equation. What I came up with after some digging around on the ...
2
votes
0answers
14 views

Does Hall Effect increases the resistance of a wire?

If a current in a wire is flowing perpendicular to a magnetic field, the Hall effect will be observed, which is caused by the forces from magnetic fields 'pushing' the electrons to one side or the ...
2
votes
0answers
314 views

Are the poles of a hollow electromagnet on the ring or in the center?

Question: Will this work as I've shown it here, more or less, or will the iron cylinder being hollow produce results not shown? Topic: I'm experimenting with magnetic fields and have been testing ...
2
votes
0answers
1k views

How to calculate magnetic pole strength?

I have 2 magnets. I need to know the force between them. In a previous Phys.SE question, conclusion was: we need to use a dipole-dipole interaction equation, which included m, which the magnetic ...
2
votes
0answers
36 views

What is the lifetime of an induced magnetization in a para/diamagnetic material?

To the best of my knowledge thermal fluctuations are responsible for washing out any effective magnetization, once the external field is switched off. Since thermal fluctuations need some time to ...
2
votes
0answers
182 views

Current to cancel Earth's magnetic field

I'm making a lab report where I've used a Helmholtz coil and a magnet to find Earth's magnetic field intensity in the area by relating the frequency of oscillation of the magnet when a certain current ...
2
votes
0answers
146 views

Magnetic Field at center of solenoid - Is this correct?

I've seen some different ways to compute tha magnetic field at the center of a solenoid, and sometimes people say that the result $B=\mu_0 n i$ is just an approximation. Well, I've thought on this way ...
2
votes
0answers
90 views

Magnetic Field versus Line Charge

Isn't a magnetic field basically an electric field originating from a line charge, but as seen in a boosted frame? I mean, that's where the relativistic explanation comes from right?
2
votes
0answers
53 views

Is it possible to measure outside magnetic field from inside a car?

I know that I can detect a vehicle by using magnetic field. I can see obviously difference in signal when a vehicle pass. But I don't see that when measuring in a car. Is it possible to measure ...
2
votes
0answers
51 views

What name would you give to the method of approximating an arbitrary magnet with many smaller dipoles?

Let's say I had an arbitrarily shaped permanent magnet, with total magnetic moment $M_{0}$. Ways to calculate the magnetic field of this magnet include an analytic solution (if one exists), as well ...
1
vote
0answers
48 views

Magnetic field derived from a scalar function

Question: Show that $\mathbf B = \hat r \times \nabla g(\mathbf r)$, where $g$ is an arbitrary scalar function, is a plausible magnetic field. What current density $\mathbf J $ can produce ...
1
vote
0answers
9 views

Would the charges on a superconductor near an another charged conductor move and produce magnetic field?

When there is a charged conducting object near an another charged conducting object the charges on these objects accumulate to the sides where the closest points between these objects are. However, ...
1
vote
0answers
25 views

Modeling magnetic field shielding

I am wondering what is the best way to model magnetic and electric field shielding from a magnetic dipole in the near field? For example, let's say you have a coil of current carrying wire in the x-y ...
1
vote
0answers
29 views

Magnetic flux and flow of electrons

What does change in magnetic flux mean? How can you change magnetic flux? How does a change in magnetic flux influence a current of electrons (electricity)?
1
vote
0answers
35 views

Physical reason for magnetic mirroring?

I understand the mathematical derivation of magnetic mirroring, which usually starts from the conservation of the magnetic dipole moment (e.g. in a plasma). But physically: a mirrored particle is ...
1
vote
0answers
46 views

Explain the infinitude of magnetic flux about a finite length of wire

Ok so it is clear the flux caused by an inductor is limited. If I integrate about a flat spiral inductor I will find that the flux lines going up are a fixed quantity. Since every flux line going up ...
1
vote
0answers
59 views

Penetration and skin depth in 'metallic' magnetic induction tomography (classical electromagnetism)

Does anyone know how AC magnetic fields behave in 'metallic' magnetic induction tomography (MIT). Do they form a magnetic circuit around a metallic specimen or penetrate through it, or both? This ...
1
vote
0answers
35 views

How the Bloch sphere of a Hahn echo in NMR looks like? 90-t-90-t-echo

I have tried to find in the literature a proper nice and beautiful Bloch sphere to describe the trajectory of a nuclear spin, starting in z-axis, using a pulse sequence of an initial 90º pulse with ...
1
vote
0answers
27 views

Magnetic needles in elastic media

I am studying a system with magnetic needles in a elastic media. The (two-dimensional) system is composed of $N$ magnetic needles distributed in an elastic matrix with Young's modulus is $E$. The ...
1
vote
0answers
51 views

Remotely changing superconductor levitation height?

I want to be able to modify the height of a quantum locked superconductor. My original plan was to levitate the superconductor over an electromagnet and modify the current to said magnet (increase the ...
1
vote
0answers
24 views

Sphere in homogenou magnetic field

I have to find out the magnetic dipole moment of sphere in homogenou magnetic field in the limit $\mu_r\rightarrow+\infty$. I don't know what does the condition $\mu_r\rightarrow+\infty$ mean. Does ...
1
vote
0answers
44 views

Quantum Locking Superconductors on Earth's Magnetic Field

Is the earth's magnetic field strong enough to hold a quantum locked superconductor, or the superconductor wouldn't be able hold its own weight? How strong should be the earth's magnetic field to ...
1
vote
0answers
49 views

Freely Falling Bar in a Magnetic Field

I have a horizontal bar on vertical rails and we can consider that does not exist any friction. Perpendicular to the plane of the rails it exists a magnetic field $B$. I am asked to find the ...
1
vote
0answers
50 views

Conformal mapping for calculating magnetic reluctance

I work currently on the calculation of magnetic resistance for a air-gap of an electrical machine. For this I am using conformal transformations. I am doing this on a 2D slice. As the machine is ...
1
vote
0answers
103 views

Currents and magnetic fields produce forces that affect things they're not touching?

I was doing this past paper and am a little confused by question 5) part c)ii) I correctly calculated that the force acting on the rod due to the magnetic field is 0.016N but I can't see how ...
1
vote
0answers
35 views

EMF & Magnetic force at the same time?

A conductor is placed in a magnetic field, current starts to flow, and the wire experiences the Lorentz force of $x$ Newtons. However, what confuses me is that $x$ is a value that is calculated from ...
1
vote
0answers
93 views

Magnetic monopole

I've been watching a lot of videos claiming to make monopoles either by dropping the temperature to 5k (-268° C) and splitting the magnet or by pouring molten metal through an induction system and was ...
1
vote
0answers
611 views

Calculating the electro magnetic field strength needed to repel a permanent magnet

I have a design where a permanent magnet is placed on top of an electromagnet. When the electromagnet is powered off, the permanent magnet is attracted to the iron core of the electromagnet. When the ...
1
vote
0answers
175 views

Explanation for the physics behind magnetic monopoles?

Ok so I am looking for a simple explanation of how the process is done from the information I could access and the knowledge I was allowed I have the idea that it is a matter of quantum physics and ...
1
vote
0answers
64 views

Demagnetization of a permanent magnet and lenz's law

This video ( http://www.youtube.com/watch?v=Vs3afgStVy4 ) demonstrates lenz's law, if the current produced by the magnet fall induces an opposing magnetic field , after many tries , can this field ...
1
vote
0answers
679 views

Magnetic field of solenoid in cone shape

I have done some drawings of the magnetic fields of cone shaped solenoid electromagnets. I based this on the work of Tesla and some explanations of Bashar, known as the Bashar Cones. I found very ...
1
vote
0answers
267 views

Two magnets with Iron truncated cone or pyramid. How low inclination can the truncated cone or pyramid be made?

Two magnets with Iron truncated cone or pyramid: Frustrum How much low inclination can the truncated cone or pyramid: Frustrum be made, without non homogeneous lines of magnetic field coming out from ...
1
vote
0answers
67 views

Maximise magnetic force at one point while minimizing at another

Is it possible to have a magnet that attracts one object strongly, but not another object behind that first object? Given an (electro-) magnet M above two thin parallel steel sheets P1 and P2 in the ...
1
vote
0answers
35 views

Potentials in Helmoholtz Theorem

I read about Helmholtz theorem on the Griffiths (Introduction to electrodynamics) and in the appendix B it shows how to use the Helmholtz theorem to determine the field F starting from the potential. ...
1
vote
0answers
875 views

Calculation of magnetic force magnitude from a parmenant magnet

I was wondering how strong a magnet should be in order to be able to horizontally attract 0.2 Kg of pure iron at a distance of 0.3 M. Since I know nothing about magnets, I started looking for ...
1
vote
0answers
84 views

How to size an electromagnet

How can I size an electromagnet? For example if I would to attract a mass of $x$ kg what are the calculations that I must do to size the ferromagnetic core and of course the solenoid? And thus, how ...
1
vote
0answers
205 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
vote
0answers
131 views

Is there an equation for the magnetic field of a conductor attached to a magnet?

Let's say I have a hollow conductive rod, 10mm diameter (O.D.), and I place a magnet of known strength 50mm up the shaft. What is the microTesla (mT) or Gauss (G) of the magnetic field (or flux ...
0
votes
0answers
10 views

How can you relate magnetic dipole moment using bound current density?

This was on my midterm last week, the question ask us to use bound current density to compute magnetic dipole moment
0
votes
0answers
13 views

How to find force acting on ferromagnetic material when it is placed in external magnetic field?

When we bring magnet towards ferromagnetic material ( like iron nails), then material gets attracted towards magnet. Since there is motion of material, there must be force acting on it. How to find ...
0
votes
0answers
8 views

Strongest Magnet Material - Theoretical Limits?

In terms of field strength the current best (AFAIK) is NdFeB with small magnets capable of producing strengths on the order of one Tesla. Is there a theoretical upper limit on the field strength of ...
0
votes
0answers
32 views

Electrolysis of Paramagnetic Ferric Chloride in Water

I'm trying to settle a bit of a debate between a friend and myself over the cause of an effect observed when dissolving Ferric Chloride, Iron(III) Chloride (FeCl3), in water and supplying an ...
0
votes
0answers
12 views

Calculate rotational duration of magnetic levitation inside a vacuum chamber?

Background Numerous examples show rotating pyrolytic graphite (or similar diamagnetic material) that can be moved using a laser. Problem The problem has the following objects: An N52 grade ...
0
votes
0answers
11 views

Near field and Nuclear magnetic resonance (NMR)

Why does Nuclear Magnetic Resonance (NMR) physics not concern itself with near field physics? All resonance wavelengths in NMR are much larger than bough sample, pick-up coil and excitation coil. ...
0
votes
0answers
31 views

Calculation of Magnetic Field Lines

I am doing some research on how to calculate magnetic field lines for a bar magnet. So far I have found the following equations: \begin{align} \frac{B_r}{B_\theta} &= \frac{d_r}{rd_\theta}\\ ...
0
votes
0answers
16 views

How big can be gradient of magnetic induction (in lab)

I'm thinking about magnetic levitation and how big force can push a diamagnetic when we put it in inhomogenious magnetic field. As far as I know, force exerted on a diamagnetic is proportionald to ...