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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What is the $\mathbf{H}$-field inside and outside the magnet?

A permanent cylindrical magnet with diameter $D$ and length $L$ possesses an uniform magnetization $\mathbf{M}$ going in the $z$-direction in a cylindrical coordinate system. The magnet is placed with ...
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How much of a “magnetic B field” can be expelled or shielded by a spherical superconductor or mu-metal sphere?

In a standard average 4 inch square magnet, What is the value of the Magnetic B field vector at a specified moment in time for such a magnet? Of that number, what is the direction of this particular “...
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What is the magnetic field of a uniform steady volume current?

Consider a slab of a material of finite, non-zero conductivity, infinite in the $y$ and $z$ directions but sandwiched by two metal plates at $x=x_{1}$ and $x=x_{2}$, say i.e. we are essentially ...
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Where does the energy go when I cut a current carrying loop?

The energy in a current carrying loop is given as $E_{\mathrm{m}}=\frac{1}{2 \mu_{0}} \int B^{2} d \tau$ If I cut the loop abruptly the current and hence the magnetic field quickly fall to zero and ...
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Curl of an Electrostatic Field

According to Maxwell's equations: $$ \vec{\nabla}\times\vec{E} = -\frac{\partial B}{\partial t}$$ But if we have an electric field that is dependent upon both the radial distance and angles, we can ...
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Ampere's law: the position of amperian loop

Can Amperian loop be taken parallel to current. I.e suppose current is in a circular loop in xy plane. And let the screen you are watching is xy plane . Can we take amperian loop in the same plane. ...
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Does an electron change its energy when the spin projection is changed?

When an electron changes its spin projection in a magnetic field does it receive or take energy? When the initial spin projection is indefinite (as is according to QM) how much is that energy?
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Can there be some magnetic field at a point without any magnetic field lines passing through it?

XY is a straight wire carrying current I. Every point on XY will form magnetic field lines in the form of concentric circles in a plane perpendicular to the plane of XY. I know that some magnetic ...
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4answers
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How can classical physics explain what happens when a charge fixed by two other charges experiences a magnetic force?

I have invented this little problem to help me understand the magnetic force better. Imagine 3 positive charges all on a line. The first charge is separated by distance D from the second charge, and ...
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Moving charge thought experiment paradox

Let’s say you have a moving charge, relative to a stationary observer. They measure that it has an electric field $E$ and a magnetic field $B$. Because the observer is stationary, they experience no ...
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Conservation of energy in superconducting transitions with Meissner effect

In Type I superconductors the transition from normal to superconducting state occurs exactly at its transition temperature. Does this mean that we could theoretically use only a little bit of energy ...
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Why are small planar current loops of sufficiently small size interesting? (magnetic moments)

In the book Basic Laws of Electromagnetism by Igor Irodov, He introduces force on a closed current-carrying loop as; $$ F = \oint I \vec{dl} \times \vec{B}$$ And then he states the most interesting ...
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What will happen if current can travel through the soft iron core of a transformer?

(Here's my understanding just in case if I misunderstood something) I understand that for order to induce a voltage on the other side of the transformer or in the secondary coil even though there's no ...
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What speed components should I consider to calculate the radius of a particle's spiral path in a uniform magnetic field?

Considering that I have a uniform magnetic field given by $\vec B = B_0 \hat k$ and $\vec v = (a\hat i,b\hat j,c\hat k )$. Taking into account that the radius of the spiral path can be acquired by $R ...
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Does something change in a magnet when an electron crosses its lines?

An electron can cross the magnetic field of a steady magnet and flip its spin. What changes in the body of the magnet? Does some electron inside flip its spin opposite to that of the passing electron ...
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How to calculate flux in a helical wire

We have a wire going around in a helix (just like an inductor) and a constant magnetic field exists along its axis throughout the space. How do we calculate the flux through it? I can't understand ...
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How does the diameter of a coil affect the time it takes for a magnet to pass through?

I'm thinking of doing an experiment based on the question. But I have no idea if it will work. I've tried finding things on the internet, but they all talk about the diameter of the wire, not the coil....
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Magnetic flux as a function of distance experiment

For my electrical engineering senior design I created an experiment to test magnetic flux (more voltage) increase from a material in a coil of wire. There is a large sending coil with A.C. voltage and ...
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1answer
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Magnetic force on a stationary body

A charged particle near a current-carrying wire does not experience a magnetic force when its velocity is equal to $0$. So why does a compass needle kept near a current carrying wire experience a ...
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A proton (mass $m$ and charge $e$) and an alpha particle ($4m, 2e$) are projected with the same kinetic energy. Then comment on their radius [closed]

My doubt is that I have two equations for radius. $$ r=\frac{mv}{eB} $$ $m$ is mass, $v$ is velocity and $B$ is the magnetic field strength. Similarly in terms of voltage we have equation: $$ r=\sqrt{...
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Wavefunction in external electromagnetic fields

If we consider a spin in an external magnetic field, it starts to precess around the vector of the magnetic field. The same should be true for any angular momentum. But what does this mean for the ...
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Orientation of an electric dipole in an external magnetic field

I am wondering the following situation: Assume you have an atom in an external magnetic field. You can choose the direction of the external magnetic field as the quantization axis. Now, the external ...
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1answer
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Do switchbacks occur in the radial direction of the solar wind magnetic field?

My question is: When we are talking about switchbacks, do we mean switchbacks in the radial component of the magnetic field or in the total magnetic field?
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How is magnetic moment of a surface current defined?

For current loops the definition of magnetic moment is $\textbf{m}=I\int d\textbf{S}$. But say I've a cube with a surface current, how can we define magnetic moment in this case?
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What's the relation between degeneracy and $\pi$-flux

Ring with magnetic flux Assuming a particle locates in a ring which circle a magnetic flux, the Hamiltonian is: $$\hat{H}=\frac{1}{2 m}(\hat{p}-A)^{2} \rightarrow \frac{1}{2 m}\left(-i \partial_{\phi}...
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Rotating current carrying loop

Consider a circular loop of wire fixed on the rim of a wheel. This wire carries a current 'i' in it. When the wheel is at rest, which basically means that the current carrying loop is at rest, the ...
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Precession of the Magnetic Moment around B

Equation 1.1.31 in this picture. How did the author reach to this solution from equation of motion? would anyone please explain it to me. I tried to derive it but no luck.
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Why ray goes down when applied a magnetic force between it in the JJ Thompson experiment?

I have a question! I was learning about JJ Thomson's Cathode Ray Tube experiment and I understand why the ray goes up when it passes through a Wien's filter, but I cannot plenty understand why it goes ...
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Why is a magnetic field of a permanent magnet not considered energy?

The first law says you can’t create energy. OK, but you can give energy to a ferromagnet and magnetize it. Then you can magnetize as many other ferromagnetic materials as you want, and not diminish ...
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What are the north side and south side magnetic metals called?

What are the two metals that cause the repel force of a north side magnet, and the attract force force of a south side magnet?
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Does spin precession stop immediately after leaving Stern-Gerlach apparatus and split into the orthogonal direction of precession?

A small concept I'm a tiny bit confused about. Sakurai in the introduction to quantum mech introduces the Stern Gerlach experiment. According to his discussion, an $S_{x}+$ particle that goes into a ...
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Does the Magnetic Field do work in Quantum Mechanics?

Let's say I have an electron in an infinite potential well. The Hamiltonian is given by: $$ \hat H | E_n \rangle= \frac{\hat p^2}{2m}| E_n \rangle $$ with $p$ being the momentum and $m$ being the mass....
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Deriving force acting on magnetic dipoles using the Lorentz force

I was always taught that classically all electromagnetic phenomena are encapsulated in the Maxwell equations and the Lorentz force formula for point charges: $$ \vec{F} = q\left(\vec{E}+\vec{v} \times ...
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How should the magnetic force between two magnets be calculated effectively?

I have read this Wikipedia page, but I can't understand it. In this picture from that page, in the formula, there is just one flux density, but what about the flux density of the second magnet? What ...
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Magnetic field strength attenuation: how to estimate if a magnet will affect another across a barrier such as wood or stainless steel?

I need to be able to get a compass needle (a magnet) to be affected (i.e., moved) by another magnet ("magnetically coupled"). These magnets are on opposing sides of a solid barrier of ...
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Why is magnetic flux conserved in a magnetic field [closed]

Why is magnetic flux conserved in a magnetic field? What rule tells this?
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Magnetic Field calculated from Magnetic vector potential [closed]

Reference : $^{\prime\prime}$Physics of Atoms and Molecules$^{\prime\prime}$ by B.H.Bransden and C.J.Joachain, 1983 Edition. In $\boldsymbol{\S}$4.1 The electromagnetic field and its interaction with ...
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1answer
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How to determine the direction of inductional current in the ring? [closed]

The permanent magnet is being moved away from the ring. How to determine the direction of the inductional current in the ring? Here's what I've tried. Magnetic field lines go from the North pole of ...
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2answers
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When a particle changes its spin orientation is it instantaneous?

A change of magnetic field caouses an electric field and an associated potential which is as high as the time derivative of the magnetic field.So is it possible that the change of the spin should be a ...
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1answer
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Does an non-moving electrically conductive metal become magnetic in a full-DC offset AC field?

Let's assume an electrically conductive object made of metal is static and does not move. Then let's apply an outer electric field. Clearly, a constant DC field would not induce any currents and ...
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1answer
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Why is the impedance of an electromagnetic wave written as a ratio between the electric and magnetic fields, $E/H$?

The 'impedance of free space is written like this, too, as the absolute value of the $E$-field over the absolute value of the $H$-field. What does the ratio of the strengths of the two fields of an ...
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2answers
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How to find the direction of the magnetic field in a toroidal inductor?

I drew sort of a picture down below (although the cell is supposed to be an ac supply). I don't understand which direction the magnetic flux? This is because, the current-carrying wire has individual ...
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Is this analogy of Induced emf correct?

I have searched PSE (and many other sites on internet) for the theoretical reason of induced emf. All I got was that the phenomenon of Induced EMF is experimental fact and can only be mathematically ...
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Would it be possible to design a system of magnets that could disable a gun at any point in a room

For the sake of this question, let's say I were the secret service, and wanted to install a system of magnets that could disable the weapon of someone in the oval office. This should be able to target ...
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1answer
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Will back emf supports flux change?

In an inductor, back emf is induced as there comes flux change. It is said that back emf decreases as time passes (when inductor is just connected to DC source). When back emf decreases current ...
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Derivative of a delta function when using Jefimenko's equations

I was using Jefimenko's equations to solve a problem our Electrodynamics teacher sent us involving a infinite wire with current $$I(t) = q_0 \delta(t).$$ So we have to obtain electric, $\vec{E}(\vec{r}...
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How are magnetic fields 'detected'?

While reading Griffith's Electrodynamics, I didn't quite understand how magnetic fields were introduced. Electric Fields were introduced as an intermediary calculation to finding the electrostatic ...
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32 views

How to calculate Complex Magnetic Impedance from Conductivity and Complex Permiability

For a week now I've been been racking my head trying to figure out how to calculate the Complex Magnetic Impedance of a material from its properties, namely Complex Permeability, and Conductivity. But ...
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EM Waves: Are $k$ and $E$ always perpendicular?

I was learning about plane waves in class and it was stated that $k$-vector is perpendicular to $E$ which is also perpendicular to $B$-field. But is this always the case?
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What is the area $A$ in the magnetic flux for AC generator and a coil?

I am getting confused with what area do you use in AC generators and coils. Let me explain: in an AC generator, there are two coils that rotate. When using the equation - magnetic flux $= BA\cos(x)$, ...

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