# 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. ...
107 views

### 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 ...
1 vote
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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 ...
77 views

### 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 ...
1 vote
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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 ...
1 vote
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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 ...
1 vote
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1 vote
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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 ...
1 vote
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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 ...
41 views

### 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}...
1 vote
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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 ...