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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2
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1answer
364 views

Why are magnetic fields only produced by moving charges? [duplicate]

Why do charged particles only produce magnetic fields while in motion?
2
votes
2answers
260 views

accelerated charged particles and interaction with magnetic field

In high school we are taught that magnetic field perpendicular to velocity of an charged particle experience perpendicular force that causes it to move in circular path by relation ...
2
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0answers
33 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 ...
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2answers
198 views

Cause of electromagnetic induction?

The rate of change of magnetic flux through a surface (open) is related with the line integral over the closed loop binding the selected surface by one of the Maxwell's equation. But that means even ...
9
votes
1answer
406 views

Would an octahedral magnet work as a magnetic bottle?

First, let me see if I understand all this: Charged particles are curved by magnetic fields, so if the magnetic field is strong enough, the particles "follow" the magnetic field lines, in N or S ...
7
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2answers
240 views

Can a magnet magnetise an object with greater strength than it possesses?

Trivial thought ... Materials may be broadly superconductive, diamagnetic, paramagnetic, ferromagnetic. An object is magnetized by repetitive motion of a magnetic field across it's surface Say a ...
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1answer
50 views

How does bow-shock constitute evidence of a magnetosphere?

Several bodies in the Solar System are possessed of a magnetosphere - Sol, Jupiter, Saturn, Earth to name a few. With these we have the proof of spacecraft/readings from Earth. For exoplanets being ...
10
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2answers
769 views

Is it possible to levitate a toy maglev train using only permanent magnets as long as the train stays in motion?

I am fascinated with magnets, and specifically the idea of magnetic levitation. I recently purchased a Levitron toy maglev train and have enjoyed finding the perfect sweet spot at which it levitates, ...
0
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1answer
986 views

Work done by magnetic field [duplicate]

I know Lorentz force don't do any work. but I want to know whether any type of magnetic field do a work or not.
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2answers
180 views

Magnetic moment precession around magnetic field

I have a question regarding the magnetic moment of an atom. If you just have one atom, and you apply an external magnetic field in lets say the z-direction. Then the magnetic moment will precess ...
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0answers
141 views

Projects for a physics club [closed]

It's a physics club for undergraduates (first three years of university); I'm looking for projects idea that aren't too obvious like a small rocket or an electromagnet (school projects) but also not ...
1
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1answer
134 views

Magnet alignment within solenoid

Imagine I have a solenoid connected to a power supply. Solenoid produces an electromagnetic field. Now I take a permanent magnet and place it inside the solenoid. How will the magnet align itself ...
6
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3answers
573 views

How do I calculate electric fields due to currents of magnetic dipoles?

Short version of my question: Do dipole currents cause fields? I think currents of aligned magnetic dipoles cause an electric field, but I don't know how to calculate this field except in the ...
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1answer
2k views

How to find the direction of the magnetic field for an infinite conducting wire?

We've got two long straight wires carrying current of 5A and placed along x and y axis respectively current flows in direction of positive axes we have to find magnetic field at a) (1 m,1 m) b) (-1 ...
7
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1answer
186 views

When the sun's magnetic field reverses, how can “the north pole (have) already (…) reversed, and (we are) waiting for the south pole to catch-up”?

I was reading a popular news account of the sun's upcoming magnetic field reversal at http://www.csmonitor.com/Science/2013/0807/Sun-s-magnetic-reversal-means-big-changes-for-the-solar-system-video, ...
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0answers
89 views

What is the meaning of $G/cm^2$?

I'll prefix this question by stating that I am not a physicist, I am a programmer. I am working on updating a (very old) program that calculates the performance of a magnet. This whole program is in ...
16
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5answers
894 views

Does a magnetically suspended frog feel weightless?

Magnetic levitation has been used to suspend frogs in midair. I was wondering: Does the animal still feel gravitational pull? I mean: Does the frog feel like an astronaut on the ISS, or does he feel ...
1
vote
2answers
197 views

Sliding force less or equal?

Why is the force required to slide a magnet off a steel plate A LOT less than the force required to directly pull it off? The force required to pull the magnet can be: 20lb While the force required ...
2
votes
2answers
273 views

Energy of electron spinning in a magnetic field

When an electron travels in circles in a uniform magnetic field, it must lose energy because all accelerated charges radiate, and must therefore spiral down to the center. Is this energy compensated ...
1
vote
1answer
229 views

How to write the single electron spin-orbit coupling under an external magnetic field?

As we know, without the external magnetic field, the single electron spin-orbit coupling(SOC) has the form $\boldsymbol{\sigma}\cdot(\boldsymbol{\nabla} V\times \mathbf{p})$ up to a coefficient, ...
0
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0answers
77 views

Mu-metal electromagnetic core?

Is it possibile to use Mu-metal as an core for a electromagnet? Considering thats is has a very high relative permeability? Low coercive force, and low hysteresis losses. And a very very low magnetic ...
3
votes
3answers
196 views

Are Field Lines an accurate depiction of reality?

Field lines are used for explaining a wide variety of phenomenon. But is it really an accurate depiction of reality? Is it more accurate to imagine a field in a different manner. For instance, using ...
1
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1answer
126 views

Dimensional analysis of magnetic energy: dimensions of µ0 and H

When calculating the energy difference between the normal and the superconducting state in a superconductor at zero magnetic field, the result is as follows: Now I'm quite confident of this result, ...
2
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3answers
5k views

magnetic field outside a solenoid

I couldn't picture the idea behind the zero magnetic flux outside the solenoid properly.My teacher explained it as"Components of the magnetic field in other directions are cancelled by opposing fields ...
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0answers
75 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 = ...
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2answers
116 views

Tale of two magnets

Please help. My example: You take a sheet of steel and suspend it in the air. Then you take a permanent magnet (i.e. a neodymium magnet) and attach it to the sheet of steel and from that you suspend ...
0
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2answers
1k views

Is there a relation between the magnetic field force of the earth and the gravitational force between the earth and other bodies?

According to Newton's Universal Law of gravitation, we can say that a huge body of mass will attract another body of mass within a short range, however, if both bodies are for instance magnetic, ...
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0answers
142 views

What happens if torque = 0?

I am trying to understand torque on a current loop which is placed in a uniform $\vec{B}$-field. (http://i.stack.imgur.com/oNO8a.jpg) It says that $\vec{F}_2$ and $\vec{F}_4$ have the same ...
2
votes
0answers
48 views

Is it possible to generate usable electricity from the motion or magnetic field of the Earth? [duplicate]

Let me start by saying that my knowledge of physics is almost nil (only high school level and I pretty much forgot everything) so bear with me, if I am asking naive questions the answers of which may ...
0
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2answers
105 views

Applying the right-hand rule for magnetic forces

I am confused about the right-hand rule for the Lorentz force. I am using same method as Brightstorm.com is: http://www.youtube.com/watch?v=LK7hv4LX3ys But for some reason it does not match op with ...
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1answer
325 views

Why is the Maxwell Stress Tensor symmetric?

What is the physical meaning of the Maxwell Stress tensor symmetry?
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0answers
32 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. ...
2
votes
1answer
381 views

What is the meaning of a constant magnetic scalar potential?

Let a spherical shell of inner radius $a$ and outer radius $b$ have a uniform magnetization $\mathbf{M}=M\,\hat{\mathbf{z}}$, $\hskip2in$ I've found that the magnetic scalar potential ...
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vote
0answers
812 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 ...
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0answers
78 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 ...
41
votes
8answers
3k views

How can Magnets be used to pick up pieces of metal when the force from a magnetic field does no work?

I learned that the force from magnetic fields does no work. However I was wondering how magnets can be used to pick up pieces of metal like small paperclips and stuff. I also was wondering how magnets ...
2
votes
0answers
153 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 ...
3
votes
1answer
556 views

Magnetic field insulators

I was wondering if there is any way to stop the magnetic field, without having the insulator turned into magnet. Let me present this as a simple case, there is a magnet to the left and a piece of iron ...
2
votes
0answers
108 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 ...
11
votes
2answers
2k views

Is Biot-Savart law obtained empirically or can it be derived?

Well, there's already a question like this here so that my question could be considered duplicate, but I'll try to make my point clear. Is there a way to derive Biot-Savart law from the Lorentz' Force ...
0
votes
1answer
474 views

From where do the permanent magnets get energy from? [duplicate]

I have a doubt about permanent magnets. If a magnet is permanent it can attract some materials permanently. Attracting something involves energy. If a permanent magnet can do this forever, from where ...
5
votes
2answers
2k views

Magnetic force doesn't do work and therefore can't change the KE of a particle?

I am having a real hard time understanding the principles behind a question I've come across during test prep. Here is the question: Q: A proton and an electron are traveling in the uniform ...
0
votes
1answer
64 views

Superconducting magnet

This is a somewhat more detailed question related to this one. The problem I want to solve is problem 1 here. What I tried: a) From $V=-L\frac{\mathrm{d} i}{\mathrm{d} t}$, we can integrate and ...
3
votes
0answers
201 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 $r$, ...
1
vote
1answer
482 views

Superconducting diamagnetic sphere in uniform magnetic field

What is the size of the magnetic dipole moment $\vec m$ of a superconducting diamagnetic sphere $radius=R$ in a uniform magnetic field $\vec B_0$? Since there is no free current, we can solve for ...
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vote
3answers
133 views

Field At Magnetic Dipole

Suppose I have a pure magnetic dipole $\mathbf{\vec m} = m\hat z$ located at the origin. What is the magnitude of the field $|\vec B|$ as $r\to 0$? In other words, what is $\lim_{r\to ...
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2answers
247 views

Work on Ferromagnetic Object Due to Solenoid

I've been going through some equations and such trying to determine the work done by a solenoid on a ferromagnetic object. I have the following: Magnetic field due to solenoid: $\vec{B} = ...
2
votes
1answer
105 views

Magnetic Force on a Loop and number of turns

Suppose we have a rectangular current-carrying loop with current $i$, then we know that the magnetic force on each side can be found as: $$F=iL\times B$$ Where $L$ is the vector in the direction of ...
0
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1answer
652 views

Magnetic engine [closed]

Is it possible to mimic crrent engine design (to some extent) by replacing the cylinders with opposed magnets? A device interupts their natural desire to push away from each other allowing them to ...
3
votes
2answers
483 views

Why the magnetic flux is not zero?

If $\vec{\mathbf B}=B\vec{\mathbf a}_z$, compute the magnetic flux passing through a hemisphere of radius $R$ centered at the origin and bounded by the plane $z=0$. Solution The hemisphere and ...