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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Finding the Magnetic Field Due to a Triangular Wire Loop [closed]
Beginning with the Biot-Savart Law, find the magnetic field at point (1,1) in the x-y plane if there is a current of 1A that flows around a right triangle. The triangle has sides that extend from the ...
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How does this physics demo work? [closed]
I saw a demo (and tried it myself) that is similar to a rail gun, but isn't really one. It uses magnets on the ends of the armature, sort of like wheels that are rolling. I am familiar with how a ...
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Why does iron fillings form crevices when placed in a magnetic field? [duplicate]
If we get magnetic field lines on a piece of cardboard, shouldn't it form a gradient of metal pieces across the board (thick layer of metal pieces near the magnet and thin layer of metal away from ...
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In what direction would current flow in the coil?
I have two circular coils facing each other in parallel. Through one coil current flows. I move the second coil in a parallel fashion.
What is the direction of current induced on the moving coil?
Acc. ...
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How does a magnetic field interact?
I want to understand the way magnetic attraction/repulsion works. Yes, I know there is a field but what do we really mean by that?
When it comes to light I understand that if I shine a torch towards ...
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When a magnetic ball passes through a copper pipe vertically
Let's say a magnetic ball passes through a hollow pipe, which is a conductor (copper), vertically. We can observe that its acceleration is decreased when compared to a free gravitational fall.
By ...
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Magnetic Scalar Potential of Infinite Wire
While working on a question about magnetic scalar potential, I encountered a challenge. The question posits that the magnetic scalar potential, denoted as $\phi$, takes the form $\phi = -\frac{I}{2\pi}...
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Atom thruster using neutral atoms
Can we build up a thruster like this:In the picture there is the "awful" Rutherford atom but it gets the point across:
The negatively and the positively charged plate make up a electric ...
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What is the meaning of $\vec H$ with respect to the total field?
Now before saying anything, I have seen the similar questions in this page regarding $\vec H$ but no one has fully convinced me yet, since I will try to give another perspective to this question.
We ...
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How current is induced when there is a change in external magnetic field?
If still charges in a wire loop do not respond to a(or have their own) magnetic field, then how is current is generated by changing a magnetic field? And why only a changing magnetic field? What ...
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Explaining Faraday's Law With Lorentz Transformations of $E$ and $B$ Fields
I've searched around for this but haven't come across a totally satisfying explanation yet. I'm trying to build a relatively simple model of how the Lorentz Transformations of the $E$ and $B$ fields ...
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Finding direction of Lorentz force and Magnetic Field for Circular Coil
I am trying to understand the two RHR's and can't seem to figure out this simple problem.
Say I have a circular coil with current flowing clockwise. Then by the 'curl' RHR the magnetic field must be ...
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Griffiths Electrodynamics rotating sphere magnetic potential
I've been working on this problem for some time now and can't manage to understand why it is wrong, although I know it evidently is. I've also found questions on the same exercise in the Stack ...
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Maximum force of a metal ball going trough coil
I've been trying to figure out the maximum force of a metal ball going trough a coil.
I have:
$$ m=\chi_m V B \qquad B=N \mu_0 I R^2 \frac{1}{2(x^2+R^2)^{3/2}} $$
Also that $F=(m\cdot B)'$. However, ...
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How does $ \vec{B}$ change when flux surface $A$ gets smaller?
So I am still a student and I just learned the basics of flux. And my teacher told us that flux ($\phi$) is equal to the magnetic field $B$ $\times$ the area $A$ $\times$ the angle of the area $\cos{\...
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How does an Electromagnetic Accelerator work?
I've recently watched this video about an electromagnetic ring accelerator. I get how it works:
it uses controlled electro-magnetic coils to accelerate metal balls'
Passing trough one of the coils ...
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Can a magnet stop when falling through a copper tube? [closed]
It is known that when a magnet falls through a copper tube, it slows down according to the Lenz's Law. So theoretically if the magnet falls fast enough, can it completely stop for a moment?
I have ...
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Magnetoresistance and Ionic conduction in mixed conductors
I've been facing a question recently on ionic conduction and have not had much luck coming across resources to reference (if there are some please point me in their direction!)
In a mixed conductor ...
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Integrating current density for cylindrical symmetry
Considering a constant current density, $\vec{J}=\frac{I}{A}\hat{k}$, and also assuming there is no displacement current in the situation, how would one apply Maxwell-Ampere's law? I keep running into ...
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Will the magnetic lines close as depicted? 3-d horse-shoe magnet
Consider the iron shape with grey in the following figure.
Assume an electric current is ran as shown. Will the generated magnetic lines look as depicted? This wants to be a 3-d version of the "...
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Magnetic force acting on a current loop while next to a current carrying wire
With I1=20A and I2=30A, find the net magnetic force acting on the loop.
I am not sure how to even approach this problem. I know that the magnetic field of the wire is $\frac{\mu_0I}{2\pi r}$ and that ...
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Mathematical expression for self-inductance constant $L$?
Is there a mathematical expression for what the value of $L$ (self-inductance constant) is for a given geometry? I've tried to come up with something, but I don't know if it's right or not...
$$\phi_B=...
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How does a magnetic moment move in static external magnetic field?
I have a confusion. At one hand, magnetic moment is forced to align with an external static magnetic field; on the other hand, a magnetic moment can precess around an an external static magnetic field ...
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Can the variation of the repulsive magnetic flux related to the variation of distances between two permanent magnets be measured with a Tesla meter?
I would like to calculate the repulsive force between two permanent magnets in a different variations of distance between the two polarity faces.
Can the different distances associated to different ...
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How does a compass behave on magnetic south
At school, we have been going through magnetism. I was thinking about compasses and how they worked, but this question stumped me:
“Imagine you are standing on the magnetic South Pole. Now, you use a ...
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Magnetism and potential energy - Energy Harvesting
I know and understand that a generator comprised of solely permanent magnets can not work. From my understanding, it basically has to do with the fact that when you pull magnets appart or push them ...
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Magnetic filed at a Helmholtz coil center
I understand that a magnetic field, B, at a center of a circular coil is:
\begin{equation}
B = \frac{N \mu_0 i}{2a}
\end{equation}
where $N$ is the number of turns of the coil, $\mu_0$ is the ...
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Is the magnetic field generated by a surface current always a vacuum field?
I am wondering about this since usually if there are no current distributions then we would obtain a vacuum field since $\nabla \times \mathbf{B} = \mu_0 \mathbf{j} = 0$ from Ampere's Law.
For the ...
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Why does the direction of the magnetic potential vector follow the current?
In Griffith's textbook, it is said that the vector potential $\vec{A}$ usually points in the direction of $\vec{J}$:
This was also pointed out in class.
However, I don't understand why it should be ...
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What is the intuitive reason why Ampere's law is incorrect?
I don't understand why Ampere's Law for magnetic fields is wrong. So initially, we got taught it as the following:
$$\vec\nabla\times\vec{B}=\mu_0\vec{J}$$
and this turns out to be wrong. I also ...
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Are the $H$ and $M$ fields parallel?
I would like to know if the $H$ and $M$ fields are always in the same (or opposite) direction. If not, are there special conditions where it is always true?
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Could a closed looped of wire with current move itself?
The question starts from this:
Place two tiny current segments on $(1,0,0)$ and $(0,1,0)$, each heading to positive $x$ direction and positive $y$ direction. By magnetic force $dF=idl\times B$, the ...
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Connection Helmholtz free energy and $H,M,B$ fields
Consider a magnetic system subject to a magnetic field. Here we work with the fields $H,M,B$.
Now, how does a change in the Helmholz free energy depend on $H,M,B$? I have three sources that seem to ...
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Can magnetic field effect the charge which produce this magnetic field?
A Moving charge makes magnetic field. Then a magnetic field produced by one moving charge can effect this charge which make this magnetic field??
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Magnetic Field of Earth and Turbulence of plasma
We generally know that plasma turbulence creates magnetic field (here, I have assumed that it happens through the dynamo effect). it is also affected by magnetic fields. Is it possible that plasma ...
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Electron Orbit at the Null Point (DC sputter coating)
This situation pertains to 'thin film sputter coating.'
Suppose I have some magnets in between a high voltage anode and cathode in a suitable vacuum. I understand that the electrons get trapped in the ...
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Why are the total and free EM fields mixed together?
For calculating the work done on a medium by an electric field: $đW = \vec{E} \cdot d\vec{P}$ but for magnetic fields: $đW = \mu_0 \vec{H} \cdot d\vec{M}$. For impedance, $Z = \frac{E}{H}$. Why is the ...
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What this thing is and what it's used for? [closed]
Images:
I'm not sure if this is the right stackexchange to ask this question but i haven't found a "gas display detection and measuring devices" stackexchange so physics seems like a ...
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What is the relationship between the distance of a current carrying wire and a dipole magnet's magnetic field strength?
For school, I'm doing this experiment where I measure the change in magnetic field strength, between a magnet and a current-carrying wire as a function of the distance. Online after doing some reading,...
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Intuition behind self-inductance
I'm having a little bit of a hard time understanding some concepts to do with self-inductance in class.
I understand mutual inductance. That's when a loop has some time-dependent current going through ...
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Finding the vector potential
$$\nabla\times\mathbf{B}=\nabla\times\left(\nabla\times\mathbf{A}\right)=\nabla\left(\nabla\cdot\mathbf{A}\right)-\nabla^2\mathbf{A}=\mu_0\mathbf{J}\tag{5.62}$$
Whenever I try to work this out and ...
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The Curie Temperature Motor Conundrum
Suppose we have a special motor with a rotor made of nickel. The shape of the rotor is such that it has a high surface area for exchanging heat with an applied flame or with a stream of cooling water. ...
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Same behaviour of EM radiation at the polarisation grid and at the double slit?
In a diffraction grating, the EM radiation is polarised after passing through the grating, i.e. the electric and magnetic field components are aligned by the grating bars, one component parallel, the ...
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Iron bar entering solenoid [closed]
I found this MC question that asks about a soft iron bar entering a solenoid:
At first, my answer was (B) because the iron bar should increase the magnetic field induced by coil M and, according to ...
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Magnetic field outside a toroidal surface with a sheet current
The integral from of Ampere's law is $\int \mathbf{B}\cdot d\mathbf{l} = \mu_0 I$. Let's say our contour of integration $\mathbf{l}$ is a contour on the surface of a toroidal surface. Also, let the ...
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Magnetic field lines at the center of the magnet pole, how do they look like?
Magnetic field lines are loops, so at the surface of a magnet pole they look like this? there is a dead zone at the center where there is no lines/magnetic field present?
Or lines converge in the ...
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Problem with derivation of $U_B=-\mu \cdot \vec{B}$
I'm trying to prove that $U_B=-\mu \cdot \vec{B}$, but I keep running into an annoying dead end in my proof (a note about the notation my course's instructor uses: $\mu$ = magnetic moment, $NIA \hat{n}...
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Can current in a wire from a battery be called a thermodynamic quantity [closed]
Joining a metal wire to both ends of a bettery causes current to flow through it.
Also, the flowing current in turn produces magnetic field that kind of rotates around that wire.
Can we call this ...
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Dependency of Stark effect on Quantum numbers
I have read many sources which tell me that the Stark and Zeeman effects, which Bohr's theory had trouble explaining, were explained by the introduction of the magnetic quantum number. But doesn't ...
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How can electric wave and magnetic waves have any angle between them?
I have been taught that the electromagnetic length of a wave is a geometrical property that can be measured in units of length, while its amplitude (both the electric and magnetic) is not a ...
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