Questions tagged [magnetic-fields]
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 [magnetism] tag, as questions about the phenomenon & theory of magnetism do not necessarily involve the discussion of fields.
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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 a magnetic field 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 ...
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Magnetic field due to a single moving charge
The Biot-Savart law can only be used in the case of magnetostatics (constant current) so how do we calculate the magnetic field of a single charge moving at constant velocity at a distance r. I tried ...
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Why don't stationary charge feel force from a current carrying wire?
The current carrying wire doesn't apply any magnetic force on nearby charge $q$( positive stationary charge) because it has 0 velocity in lab frame. We found that there is no force on q by wire. But ...
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What is the difference between the magnetic $H$-field and $B$-field?
From Wikipedia:
"The term (Magnetic Field) is used for two distinct but closely related fields denoted by the symbols $B$ and $H$, where $H$ is measured in units of amperes per meter in the SI. $...
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Does special relativity make magnetic fields irrelevant?
I've heard that special relativity makes the concept of magnetic fields irrelevant, replacing them with relativistic effects between charges moving in different velocity frames. Is this true? If so, ...
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Are magnetic fields just modified relativistic electric fields?
Feynman's Lectures, Volume 2, says that the electromagnetic force is invariant in any reference frame, and the magnetic force in one frame becomes the electric field in another.
And Wikipedia says:
...
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Does a magnetic field do work on an intrinsic magnetic dipole?
When you release a magnetic dipole in a nonuniform magnetic field, it will accelerate.
I understand that for current loops (and other such macroscopic objects) the magnetic moment comes from moving ...
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What is the magnetic field inside hollow ball of magnets?
Setup: we have a large number of thin magnets shaped such that we can place them side by side and eventually form a hollow ball. The ball we construct will have the north poles of all of the magnets ...
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Is Biot-Savart law obtained empirically or can it be derived?
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 that this is a different question.
Is there a way to derive Biot-...
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Is there an intuitive explanation for why Lorentz force is perpendicular to a particle's velocity and the magnetic field?
The Lorentz force on a charged particle is perpendicular to the particle's velocity and the magnetic field it's moving through. This is obvious from the equation:
$$ \mathbf{F} = q\mathbf{v} \times \...
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What prevents this magnetic perpetuum mobile from working?
As a child, I imagined this device, which may seem to rotate indefinitely. I have two questions.
Is this perpetual motion machine already known? If it is, could you please give some references?
What ...
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Can someone please explain magnetic vs electric fields?
I've looked through about 20 different explanations, from the most basic to the most complex, and yet I still don't understand this basic concept. Perhaps someone can help me.
I don't understand the ...
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What is the mechanism by which magnetic fields do work?
I've seen some conflicted answers to this question in texts and on the web, in the case of a dipole, for example.
Do magnetic fields do work directly, or is it their induced electric fields that do ...
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Current in wire + special relativity = magnetism
Current in wire + moving charge next to wire creates magnetic force in the stationary reference frame OR electric force in the moving reference frame from special relativity due to change in charge ...
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A generalization of the Biot-Savart law for a number $n$ of wires with $n\geq 3$
This question is not a homework-exercises, but a request if exist a general formula of Biòt-Savart. We suppose that I have three or more wires traversed by incoming and outgoing currents and I would ...
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Is magnetic force non-conservative? [duplicate]
If magnetic field is conservative, then why not the magnetic force?
My professor thinks it is non conservative but he couldn't explain to me why?
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Do magnets lose their magnetism?
I recently bought some buckyballs, considered to be the world's best selling desk toy. Essentially, they are little, spherical magnets that can form interesting shapes when a bunch of them are used ...
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Can current be induced in a superconductor?
Moving a magnet close to a conductor induces a current. If it consists of a superconducting material with resistance $R=0$, then my textbook says:
Then the induced current will continue to flow ...
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What is the nature of the magnetic fields? [closed]
In this question, I am hoping to find out if there is an explanation to the magnetic hidden forces. In other words, what causes these fields?
Is there any suggested theory, or any confirmed ones ?
...
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Can magnetic fields be redirected and focused at one point?
I know that magnetic fields can be redirected, but... given a situation where you have static magnetic field over a large area, and you want to quickly change the magnetic field strength. Is it ...
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How long does a permanent magnet remain a magnet?
I have a bunch of magnets (one of those game-board thingies) given to me when I was a school-going lad over 20 years ago, and the magnets feel just as strong as it was the day it was given.
As a ...
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Mechanism by which electric and magnetic fields interrelate
I read that force due to electric field on some particle in one reference frame can exhibit itself as force due to magnetic field in some other reference frame and that electric and magnetic fields ...
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Physical interpretation of 2-forms dual to pseudovectors
Mathematically for every 3D pseudovector $x^i$ there is a 2-form $F_{ij}=\epsilon_{ijk}x^k$ such that the 2-form transforms properly under all orthogonal transformations. Therefore I would expect it ...
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Manganese has more unpaired electrons than Iron so why is Iron ferromagnetic Manganese paramagnetic?
Manganese has five unpaired electrons, but Iron has four, then why is Iron ferromagnetic and Manganese paramagnetic?
What's that property I'm missing?
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How does a magnet work?
I'm having trouble understanding how a magnet (not the field that is generated as a result but the material itself) work. The particles are aligned in a specific direction to give rise to force but I ...
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Why is there no gravitational magnetic field? (Or, is there?)
We can think that the electric field and the gravitational field operate similarly in the sense that the forms of their governing laws (namely, Coulomb's law and Newton's law respectively) are ...
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How virtual photons give rise to electric and/or magnetic field? [duplicate]
Say a neutron which have magnetic moment despite carrying no charge. Isn't both the electric field and magnetic field consist of virtual photons? So how can the same virtual photons give rise to 2 ...
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Helical motion of charged particle in external magnetic field
When an electron moves in uniform external magnetic field, with velocity not perpendicular, I understand that the magnitude of force is only due to the perpendicular component of velocity and is ...
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Muon $g-2$ experiment: is there any theory to explain the results?
The nature of the experiment has been discussed here, but my main question is this: is there any theory that has predicted the results of this experiment or are we completely clueless about what's ...
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What are the fields produced around a current carrying conductor?
If you consider a current carrying conductor, every instant an electron enters the conductor, another electron will be leaving the conductor. Thus, the current carrying conductor will not be charged (...
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Electromagnetic fields vs electromagnetic radiation
As I understand, light is what is more generally called "electromagnetic radiation", right?
The energy radiated by a star, by an antenna, by a light bulb, by your cell phone, etc.. are all the same ...
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What is the electric field generated by a spinning magnet?
Consider a cylinder of permanently magnetized material, with uniform magnetization pointing along the cylindrical symmetry axis (the $z$-direction). The magnet is rotating about its cylindrical ...
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Simple explanation to the induction from the slowly changing $\vec B$ of a solenoid in the region of $0$ magnetic field
I would like to get some elementary intuition into the problem a solenoid fed with a time-dependent current, and the resulting current that such the solenoid field would induce in a loop completely ...
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Took a picture of my laptop screen with my iPhone. The yellowish pattern in the image look like magnetic lines. How is this possible?
The pattern seems consistent with the magnetic force lines of a bar magnet.
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Direction of $\textbf{H}$ and $\textbf{B}$ inside and outside a bar magnet
I seem to have encountered a contradiction when thinking about the directions of $\textbf{H}$ and $\textbf{B}$ inside and outside a bar magnet.
Suppose that a bar magnet has a roughly constant ...
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Why do charged particles follow magnetic field lines?
This may seem like a dumb question, but I can't think of the answer. The context I am curious about is the solar wind. Specifically particles flowing out of coronal holes and following the magnetic ...
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How can I use a magnet to lift a paperclip?
This question has been asked already, but no satisfying answer came up. All the answers seem to push the problem further, but do not explain clearly what is going on.
I will reformulate it for a ...
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Frozen in Magnetic Field Lines
A perfectly conducting fluid undergoes an axisymmetric motion and contains an azimuthal magnetic field $\textbf{B}_θ$ . Show that $ \dfrac{B_θ}{r}$ is conserved
by each fluid element.
Question from ...
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Eddy current induce EMF
Q1 Suppose there is a wire having AC current so as ac current is alternating it creates back EMF whether that back emf produces current?
If yes then that current is same as eddy current or not?
And ...
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Why should Conservative forces have their curl equal to zero? (intuition)
There are several conditions that must be met in order for a force to be conservative.
One of them is that the curl of that force must be equal to zero?
What is the physical intuition behind this?
If ...
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Is there any example where electric and magnetic fields are not perpendicular?
Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
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Why are magnetic fields so much weaker than electric?
In EM radiation, the magnetic field is $ 3*10^8$ times smaller than the electric field, but is it valid to say it's "weaker". These fields have different units, so I don't think you can compare them, ...
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How does Hendo hoverboards achieve the self-propelling motion? What is the MFA?
From what I understand of the idea behind Hendo hoverboards, they use four disc shaped hover-engines to generate a self-propelling motion.
I also understand that it uses Lenz's law and eddy currents. ...
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What is the difference between Biot-Savart law and Ampere's law?
What is the difference between these laws?
Which law is more useful?
When to use Ampere's law and when to use Biot-Savart law?
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Positive work by a magnetic field
Consider a single charge moving only under the influence of Magnetic Field $\vec{B}$. The charged particle moves in a circle and the work done by $\vec{B}$ is 0. Now consider a current element in a ...
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How would the Aurora light on Earth look like if there wasn't a magnetic field?
Here are some pictures of the aurora light.
The beautiful phenomenon of Aurora is a well-known one, seen in the northern (Aurora Borealis) and southern parts (Aurora Australis) of the globe. Here is ...
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Is diamagnetism a static or dynamic effect?
When we put a diamagnetic material in the presence of an external magnetic field $\vec B_0$, the magnetic field inside the material decreases to
$$\vec B=(1+\chi_m)\vec B_0,$$
where the magnetic ...
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From where do the permanent magnets get energy from? [duplicate]
I have a doubt about permanent magnets. If a magnet is permanent it can attract some materials permanently.
Attracting something involves energy. If a permanent magnet can do this forever, from where ...
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The magnetic field of a magnetic monopole
Let us define the magnetic field
$$\vec{B} = g\frac{\vec{r}}{r^3}$$
for some constant $g$. How can we show that the divergence of this field correspond to the charge distribution of a single magnetic ...
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Why magnetic flux density is material dependent where as electric flux density is not?
Electric flux out of a closed surface depends only on the charge enclosed. So, intuitively, the number of flux lines crossing unit area is constant regardless of the material. However, the number of ...
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