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 ...

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What is the effect of a magnetic field on a plasma speaker?

I have been doing some research for the past couple years investigating the effect of a magnetic field on a plasma speaker. More specifically, if you apply a relatively uniform magnetic field in no ...
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2answers
173 views

What is the physics of tilt compensation of an electronic compass

This question concerns the physics behind the implementation of electronic compasses to find the orientation of a device. In the robotics community, 3-axis magnetometers are often used for this ...
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1answer
95 views

Pulling a bar through a magnetic field

This is a question on magnetic flux and induced voltage. I believe that this problem's answer key is incorrect, and I want to determine whether my opinion is sound. I also want to explore one ...
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2answers
168 views

Why is there no induced electric field in the experiment (Faraday's Law)

Below are three circuit diagrams for each of Faraday's experiments that allowed Faraday to come up with Faraday's Law. In Griffiths' Introduction to Electrodynamics Griffiths states (on page 302 of ...
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1answer
1k views

Why is the magnetic field stronger at the edges of a bar magnet?

I have been performing an experiment at school in which I test the force on an iron surface from the magnetic field of an electromagnet. The electromagnet has a rectangular iron core. The theory ...
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3answers
2k views

1 Tesla electromagnet?

Is it possible to create a powerful electromagnet at home? With use of a ferromagnet it seems so... Using the following formula: $B(Tesla)= k\mu_0nI$. I understand some ferromagnet's like iron could ...
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1answer
12 views

Magnetic field path on a surface with axial symmetry

$\newcommand{\dv}[2]{\frac{\mathrm{d} #1}{\mathrm{d}#2}}$ I'm trying to find the path a magnetic field line takes along an axially symmetric magnetic surface. I'm given: - $r,z$ points along a ...
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1answer
40 views

Can Ampere's Circuital law be used on an infinite number of alternating Helmholtz coils?

I have the following surface current density $$ \bar{\sigma}_s = \hat{\phi} \sin(kz) |\bar{\sigma}_s| $$ to approximate an infinite number of alternating Helmholtz coils stacked along the z-axis with ...
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Graphene - Can it produce a magnetic field?

So it's probably a quick no on this one, but since I haven't majored in physics or chemistry I have no idea if it's possible to make Graphene generate a magnetic field. Assuming power or current is ...
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1answer
113 views

Why is the quench temperature fluctuation not a concern for maglev trains?

I am having trouble discovering why temperature fluctuations and magnetic field fluctuations are not a stability concern for superconducting magnetic levitation trains. I am under the impression that ...
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0answers
115 views

Earth magnetic field [closed]

I gather that, in these days, the most common explanation for the Earth magnetic field existence and strength is the theory of convetive currents of molten iron and nickel atoms in the outer core of ...
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1answer
38 views

$B$ field around an infinite wire symmetry argument

Consider the infinity current carrying wire wire drawn below along with the three possible components of the magnetic field at a point a distance $r$ from the centre. I know how to use symmetry to ...
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7answers
310 views

Bar magnet dropped through coil

If you have drop a bar magnet through a coil so that it goes all the way through I was told the graph of emf induced in the coil vs time looks something like this: (emf induced is on y axis, time ...
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3answers
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What is the direction of area vector while calculating magnetic flux?

In my textbook, as a preliminary to Faraday's law of induction, magnetic flux is defined over a closed loop as $$\Phi_B = \oint \vec{B}\cdot d\vec{A}$$ Then it draws a parallel with electric flux ...
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47 views

Why does “liquid metal” do this?

I just watched this video where a guy uses magnetic "liquid metal" along with a standard magnet to create some pretty cool spiky shapes. The magnetized liquid, when brought near the standard magnet, ...
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0answers
14 views

Halbach array possible shapes?

Looking at images on the web most hallbachs are either rings or blocks but I have seen a couple pictures of what look to be rectangles or pyramids. They are just illustrations though and maybe ...
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1answer
27 views

How to tell apart a permanent and induced magnet which are otherwise identical?

In his educational series "Demonstrations in Physics" the late Prof. Julius Sumner Miller posed the following riddle: Given two identical bars of iron, one magnetized and one not, how can you ...
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Looking for name of mapping procedure [migrated]

I have been searching for a technique that I used 20 years ago, but for the life of me, I cannot remember the name. It is used in visualizations of pressure, temperature, electromagnetic fields etc. ...
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1answer
34 views

Relation between magnetic fields of magnets and magnetic field of currents

When I started to study magnetostatics it was said that magnetic fields are created by charges in motion, that is, they are created by currents. On the other hand, we have magnets and those have ...
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2answers
105 views

What really happen with resonance inductive coupling

I can't figure out the picture of resonance inductive coupling I can image how magnetic inductive coupling works, It scatter magnetic around one coil and if second coil being near it then induce ...
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1answer
356 views

Coercivity of a ferromagnetic material?

I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the ...
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3answers
570 views

Difference between electromagnetic radiation (EMR) and Electromagnetic Field?

I'm a freshly graduated electrical engineer. One course that I really struggled with was Field Theory, because it was a lovely assortment of vector calculus and things that were explained to me well ...
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1answer
17 views

Local form of Ampere's law

How can I find the magnetic field created by an infinite straight wire of radius $R$ and current density $\vec{j}$ using only the local form of Ampere's law : $\vec{\nabla}\times \vec{B} = \mu_0 ...
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1answer
120 views

magnetic field of a rotating ring magnet

Can the magnetic field of a rotating ring magnet induce current in a conductor? Is there a flux linkage between magnetic field of a rotating ring magnet and a conductor?
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4answers
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North and south of magnetic field

The current I is flowing upward in the wire in this figure. The direction of the magnetic filed due to the current can be determined by the right hand rule. Can we determine the north and the south ...
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2answers
37 views

Bar magnets and work - contradiction

Suppose we hold two bar magnets with opposite poles facing each other a certain distance away. We let go and the magnets fly towards each other. We observe that the magnets gain kinetic energy. ...
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1answer
39 views

Fleming's left hand rule

in Fleming's left hand rule is the direction of current showing the direction of the flow of electrons or the direction of positive charge?
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3answers
356 views

How are the Lorentz force, Maxwell's third law and Faraday's law of induction clasically related?

Faraday's law of induction can be used in any situation where the magnetic flux is changing through a closed conducting loop. While giving the correct answer, it seems to me that for the following ...
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2answers
23 views

How does magnetic field affects a charge?

If a electron is placed in a fixed magnetic field, how the electron will get influenced by it? How does magnetic field attacts/repulses the charge?
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1answer
63 views

Magnetic monopoles and special relativity

I was thinking about magnetism as a product of special relativity and the result of this approach to the magnetic monopoles. So if magnetism is a product of electricity(like electricity from another ...
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2answers
578 views

Why are magnetic field lines perpendicular to the surface of a ferromagnetic material?

It is known that magnetic field lines become nearly perpendicular to the surface of a ferromagnetic material. The quantitative proof which uses the boundary condition requires that magnetization at ...
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0answers
30 views

Do these symmetrical looking B field problems have the obvious answer?

I am struggling with two questions whose answers both appear to be trivially zero by symmetry arguments, when I was expecting more derivation to be required. Problem A), An infinitely long wire ...
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2answers
80 views

Conducting rod moving through magnetic field

If a conducting rod moves through a magnetic field which way do its electrons move? In my revision guide it shows the following picture (more or less, but the following is my drawing of it -- I ...
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2answers
44 views

Why does one call $B$ the magnetic induction?

When one studies electrostatics we have the electric field $\mathbf{E}$. This object usually is introduced as a field produced by a configuration of charges such that the force on another charge $Q$ ...
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1answer
30 views

Faraday and Lenz's laws

in my revision guide it gives the equation for Faraday's law as $$\text{induced emf} = N\frac{\Delta \phi}{\Delta t}$$ while the one for Lenz's law is given $$\text{induced ...
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1answer
23 views

What is flux linking?

In my revision guide it says, "flux linking is when emf is induced by changing the magnitude or direction of the magnetic flux." I'm slightly confused here because earlier on the page it defines ...
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1answer
16 views

Notation Comprehension - Magnetic Field vector

While studying I've come in touch with a question about Magnetic Momentum, Torque and Loops. In it the following picture was given: During the calculus of the Torque, the intensity of the field and ...
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1answer
32 views

Interacting magnetic fields

Is there a reason why two magnetic fields perpendicular to each other do not interact? If they are parallel or at a non-90 degree angle they interact. Is it because magnetic field lines can be viwed ...
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1answer
304 views

How does the speed of a DC motor depend on the size of the coil?

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 ...
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1answer
48 views

Do the relations between E/B and D/H contain higher order multipole terms?

Jackson writes in section 1.4 (third edition) that \begin{align*} D_\alpha &= \epsilon_0 E_\alpha + \left(P_\alpha - \sum_\beta \frac{\partial Q'_{\alpha\beta}}{\partial x_\beta} + \ldots \right) ...
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2answers
44 views

Could I make a magnetic foam or film by mixing magnetic dust?

I'm a developer and tinkerer more than an academic, and I'm not sure if this question, being more practical and less theoretical, will be welcome or not here. But here goes, with apologies in advance ...
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1answer
37 views

Do changing magnetic fields always produce solenoidal electric fields?

Since the curl of E is the time derivative of B, $\nabla \times \vec{E} = -\frac{\partial B}{\partial t}$ Do changing magnetic fields always produce solenoidal electric fields? For instance a ...
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2answers
419 views

Torque per unit length on infinite rotating charged cylinder

For homework I have the following question, but I am stuck on finding the torque on the cylinder. An infinite cylinder of radius $R$ carries a uniform surface charge $\sigma$. We start rotating the ...
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1answer
159 views

Using a circuit to make a magnetic balance to weigh objects

I understand that this is a homework question, but I am learning about magnetic fields and things like that and this certainly wasn't covered in the material, so my question is more about the actual ...
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0answers
33 views

Meissner effect and levitation

In a field less than critical field, decreasing the temperature below the critical temperature will eliminate the magnetic field inside a superconductor and increase the magnetic field around it. ...
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4answers
256 views

Question about magnetic force

I have some confusion regarding the magnetic force. I know that the magnetic field created by a moving charge or current EXERTS a force on any moving charge or current that is present in the field. ...
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2answers
205 views

Derivation of Faraday's law using Lorentz force?

For a stationary loop of wire with a time varying magnetic field $\vec{B}(t)$ through it. Is it possible to derive Faraday's law, using only the Lorentz force $$\vec{F}=q \vec v\times \vec B \tag ...
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2answers
35 views

what does magnetic field vector mean?

I am trying to understand what a magnetic field vector tells us about the magnetic field. I understood that a vector is just a representation of a point and how much it is moved in x,y and z direction ...
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2answers
52 views

what is the result of change in gravitational flux?

As a change in magnetic flux results in induced EMF (electromotive force) likewise what is the result of a change in gravitational flux? UPDATE: Gravitational flux according to me has only ...