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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Angular Acceleration of a wire in a magnetic field

My physics book presented me with this question: A copper wire with density $D=8960 \;\text{kg}\,\text{m}^{-3}$ is molded in the shape of a circular spire with a radius of $r=0.50\;\text{m}$. The ...
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Hysteresis curve in ferromagnetic materials

Suppose I have a ferromagnetic material that is inside a chamber where you can somehow control the magnetic field. The image represents its magnetization in function of its applied magnetic field. a) ...
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Is the magnetic field at the centroid of a closed loop connected at two different points to a battery always zero?

Given a closed 2-dimensional conducting loop, the terminals of a battery are connected at any two points on the loop (but not the same point). As an example, consider a circle of radius $R$; the two ...
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physics question [closed]

A copper wire is wrapped 65 times around an unknown core of length $28 \;\text{cm}$. The current in the wire is $800 \;\text{mA}$ and the magnetic field due to the electromagnet is $1.63 \times 10^{-2}...
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Do magnetic fields really travel with ${}c$ velocity in space?

I was thinking about a situation: In space there is our setup, a wood piece of mass $m$ and a coil and permanent magnet of mass $m$. The coil is placed a light second far from the magnet. The magnet ...
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Does ferromagnetic sheets still act as magnetic shield above the Currie temperature?

Well... Everything is in the title... Does ferromagnetic sheets still act as magnetic shield above the Currie temperature ?
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My question is about the fractionalized electric charge in graphene, how to compute it i really got no idea? [closed]

my question is about the fractionalized electric charge in graphene, how to compute it i really got no idea?
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76 views

Do magnetic fields really travel with $c$ velocity in space?

I was thinking about a situation- In space there is our setup, a wood piece of mass $m$ and two coils $C_1$ and $C_2$ and a battery with a switch connected to C1. C1 also has m mass. C2 is placed say ...
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Aharanov-Bohm effect on a scattering system

I have a scattering system with a localized potential and a hard wall. Hardwall is at the x<=0. On the x-plane at an arbitrary point (x>0), there is a localized potential that scatters the ...
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1answer
57 views

Is it possible to create a twisted bar magnet and will it have a twisted magnetic field?

I am wondering if a twisted piece of soft iron can be magnetized, and if so, will it have a twisted magnetic field? I created a 3D CAD drawing to illustrate what this twisted bar magnet would look ...
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What's the magnetic field produced by a current carrying circular loop at a point on its plane?

How do I find the magnetic field in this case? I already know about the magnetic field produced by a current carrying loop at an axial point or center but what about the point on its plane?
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Magnetic field due to a current carrying circular arc at distance $x$ from its centre

I can't visualise how the component of $B$ field perpendicular to the arc's axis will be distributed for different current elements on the arc.
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Factor before Dirac delta in magnetic dipole field formula

I bumped into this formula for the magnetic induction field generated by a dipole, containing Dirac's delta, while studying hyperfine splitting: $$\textbf{B}(\textbf{r}) = \frac{2}{3}\mu_0 \textbf{m}\...
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Spin coherent state path integral derivation

I'm trying to follow the exposition of spin coherent state path integral presented in Condensed Matter Field Theory by Altland and Simons (section 3.3, Page 134-142), and I have a problem with the ...
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Propagation of electromagnetic waves

When EM waves propagate, they produce oscillating electric and magnetic fields. How did we know this? Is there any experimenting concluding this or it this just a theory?
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I need help with this physics question on magnetism [closed]

This is for an AP physics 1 assignment and I really don't get the whole right-hand rule thing especially the specific way you need to put your right hand in order to tell the current, force, and ...
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How to generate electric current without a permanent magnet

The question is pretty simple: Can we build a device that coverts mechanical work in electric current1 without employing a permanent magnet and without access to any external source of current? The ...
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Amperian loop for different situations

Why are amperian loops always taken as circles? What if we take it as a triangle or rectangle? Give an example by taking amperian loop as rectangle for current carrying straight wire and derive ...
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Is Magnetic force different in different frames?

Suppose a charged particle moves with a velocity $v$ near a wire carrying an electric current. So, a magnetic force acts on it. If the same particle is seen from a frame moving with velocity $v$ in ...
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1answer
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Net force acting on conductor in a circular magnetic field

Suppose you have a completely straight electrical conductor with a current, travelling from the vertically downwards direction to the upwards direction. The magnetic field would thus be circular, ...
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Eddy-current testing

I heard it was possible to detect a flaws in conductive materials using two coils carrying the same current in opposite directions. More precisely, I read it was possible to do so by moving a ...
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Conservation law relating magnetic geodesics and certain Killing fields

This is going to be somewhat math-heavy, but I'd like to make physical sense of this. Consider the following setup. $(Q, g)$ is a Riemannian manifold. $A \in \Omega^1(Q)$ is a magnetic potential ($1$-...
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Inverse $n^{th}$ power law for Magnetism experiment

I'm trying to read through a lab manual for showing the inverse square law of magnetism by Gauss' Method. The following diagram is given where M is the magnetic moment of the test magnet. $H_0$ is ...
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Force due to an electromagnet

I am attempting to find the force on a piece of cylindrical metal placed beneath an electromagnet at an arbitrary distance and orientation. By modeling the electromagnet using femm software, I know ...
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75 views

Is the work done by magnetic field always zero?

In this case the current is flowing in forward direction due to which the force due to magnetic field acts towards the right and the rod moves towards right. Here in this case, I say force causing ...
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What is the connection between the magnetization of a thermodynamic system, the magnetic fields, and the free energy?

From multiple textbooks I gather The first law of thermodynamics: $$dU = \delta Q + \delta W = TdS + \delta W$$ The definition of the free energy: $$F = U - TS \Rightarrow dF = -SdT + \delta W$$ The ...
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Finding the vector potential of magnetic field via line integration

If we look at the relationship between the scalar electric potential and electric field in electrostatics, $\vec{E} = - \vec{\nabla} \phi$, we can easily invert this relationship by $$ V (\vec{r}) = -\...
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Surface Current Density

I'm trying to derive the boundary conditions for magnetic field and if I try to derive the condition for the tangential component of magnetic field. From the figure and Maxwell's law for line ...
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What are the major factors of energy coming into and leaving the Earth? [migrated]

Earth is a very special goldilocks planet which somehow maintains a useful thermal range for life. In order to do this, it must have some function of absorbing and releasing energy. If it absorbed ...
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Continuity of Magnetic Flux

I was trying to solve a problem in which I had to obtain the function of the magnetic flux through a loop over time. The way the magnetic field and the surface are defined is piece-wise, and I ...
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Magnetic field due to a line and a plane

I need to find the magnetic field produced by this arrangement Let me explain the image: The vertical line is a conducting straight line with a current being conducted. Now, the horizontal line is ...
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Force on a magnetic dipole

How to deduce the force on a magnetic dipole given by $F = \nabla(m \cdot B)$ from the Lorentz force?
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1answer
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Difference between minimal coupling $(p-qA)$ and $B \cdot L$,In Hamiltonian

It seems like when coupling an electron to a magnetic field we always use $B \cdot S$ to couple its spin magnetic moment to the magnetic field. However sometimes we couple its motion to the magnetic ...
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Why do different materials have different permeability and susceptibility values? What are the factors that decide these values?

what are the general mechanisms which resist the magnetic field through an object? I have often come across the fact that permeability and susceptibility depend on the nature of the material, but what ...
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Why is the magnetic field vector of light so weak compared to it’s electric field vector?

As this article describes, https://physics.aps.org/story/v26/st13 The magnetic field vector of light is extremely weak. It seems odd to me why this has never been explained in my science curriculum, ...
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1answer
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Faraday's Law - When do we know when it is a motional EMF or an induced electric field?

So from what I know, Faraday's law states that when there is a change in magnetic flux, an EMF is induced. This can be explained with motional EMF where when the magnet moves towards the conducting ...
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Does the magnetic force has anything to do with induced EMF in Faraday's law?

So according to faraday's law, when there is a change in magnetic flux, there is an induced EMF. My understanding: In the reference frame of the magnet, the charge is moving, hence there is a current. ...
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Is there any difference in the the electric field of a proton and an electron?

The question which I was wondering about was that how does a positive charged particle know that the other particle is positively or negatively charged? Then I thought that maybe there is some ...
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Ampere’s Law Field zero?

My textbook states that If $\int B\cdot dl=0$, it does not necessarily mean that $B = 0$ everywhere along the path, only that the total current through an area bounded by the path is zero. However ...
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Existence of torque on a dipole due to magnetic field even is the force on a magnetic dipole is zero

In chapter 7 of Introduction to Electrodynamics by David J. Griffiths, the author states the torque $\mathbf{N}$ on a magnetic dipole due to a magnetic field $\mathbf{B}$ is given by $$ \mathbf{N} = \...
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What is doing the work on a magnetic dipole in a magnetic field?

I understand that the torque acting on a magnetic dipole in a magnetic field is given by $$\vec\tau=\vec\mu\times\vec B \therefore \tau = \mu B sin\phi$$ It follows that the work done as the dipole ...
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1answer
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How to find the force on a charge that is distanced from a bounded circle with a changing magnetic field?

I've come across the following question, and when I attempted to solve it using different two different methods, I didn't get the same answer. The question presents an area of a circle, with radius $R$...
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Why are points neutral in magnetic fields?

I’m going through a couple of T/F statements in class. One I’m stumped with, “If a point in the magnetic field is neutral, it’s magnetic field vector components are all 0” At first sight it looks true ...
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At what speed does a magnetic field form from the flow of current?

When an electrical current flows through a conductor and produces a magnetic field, does the magnetic field in the conductor form at the drift speed of the electrons in its structure or the velocity ...
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Torques and forces between two magnets?

How do we typically calculate the torques and forces that two magnets with arbitrary positions and orientations exert on each other? Is it possible to, given two magnetic fields $B_1(\vec{x})$ and $...
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Line current above conducting plane

Question: If you have a line current in the z-axis with current I and a conducting plate parallel to it at distance d. The magnetic field is zero inside this plate, as is for every perfect conductor, ...
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Why is there no conduction current $i_C$ through a surface between capacitor plates?

The image is from Young and Freedman's University Physics with Modern Physics, Chapter 29 (Electromagnetic Induction). The image shows a parallel plate capacitor being charged where the current ...
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Will close-loop increase magnet force?

If I have two magnets, and I use an iron to make it a close-loop magnet with a gap. Will the close-loop magnet force at gap stronger than the force of two separate magnets?
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Torque of a three phase synchronous motor

I'm searching a way to express the torque of a three phase synchronous motor with permanent magnet in function of the current. I took as the magnetic field of the stator this expression : $\vec B(M,t) ...
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Can we interchange the quantities involved in Fleming's left hand rule?

Fleming's left hand rule states that If we stretch the thumb and first two fingers of left hand in mutually perpendicular directions such that forefinger points along B (Magnetic field vector) and ...

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