# 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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### 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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### 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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### 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 ...
### 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?
### 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 $= BA\cos(x)$, ...