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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25 views

How do magnetic fields due to random motions of charges cancel out in a current-carrying wire?

In my physics textbook, it states that magnetic fields due to random motions of charges cancel out at every point I know there's a drift velocity due to force imposed by the electric field, but the ...
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22 views

Magnetic potential for the electron

Citing my professor's book: The magnetic moment associated with the orbital motion, somewhat corresponding to a current, can be derived from the Hamiltonian for an electron in a static magnetic field ...
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Is there a Relationship between thermal Hall conductivity and coplanar/non-coplanar spin?

Does the magnitude of the thermal Hall conductivity depend on whether spins are coplanar or not? Also, if you have any theoretical references, it would be helpful if you could present them.
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Magnetic Field at centre of Hemisphere

MY APPROACH: I know that we have rotate by an angle theta from centre and take an angular element which corresponds to a ring and write the expression for field accordingly. But my main problem is ...
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2answers
35 views

Can we make stronger electromagnet by using less voltage and current but very thicker wire and more number of turns in a coil?

If we increase the number of turns in a coil, the resistance increases, to overcome this, we can use very thicker wire and keep the voltage low to keep the current constant, and by the formula, this ...
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28 views

Flux and emf induced graphs when magnet is dropped through a coil

I've been told that if you drop a magnet through a coil the induced emf and flux graphs would look like this: I understand that when the bar magnet is in the middle of the coil the emf induced is ...
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27 views

The history of Ampère's circuital law and Ampère's force law

How I know and read in the Internet that Ampere realized that two current-carrying wires can exert force on each other. Ampere's force law is: $$d^2\vec{F_{21}}=-\frac{\mu_0}{4\pi}i_1i_2\frac{\hat{r}}{...
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Particle motion in earths radiation belts. Comparison of gradient drift and drift due to convection and corrotaion

I would like to know if the drift due to the gradient of the earth's magnetic field could be balanced by the sum of the drifts due to corrotation and conviction of the earth's magnetosphere. To my ...
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23 views

Energetic radiation belt particles bounce motion period

How to show that energetic radiation belt particles experience a force along the direction of the geomagnetic field due to gradients in the ambient field strength? Also for particles ...
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45 views

WHY does a DC solenoid develop magnetic force even though its inductance is zero?

If the inductance of coil fed by dc voltage is zero then how do dc solenoids work?
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An iron nail near a magnet experiences both torque and force but a needle experiences only torque in uniform magnetic field? WHY?

This is an example from NCERT TEXTBOOK and it says that the iron nail experiences induced magnetic moment. So my question is how exactly can an induced magnetic moment produce torque+ force on an iron ...
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Magnetic flux switch , parallel magnetic path actuator, motor/generator

Can you help me understand whether this concept works or is it a misconception. The basic idea is simple, you use a permanent magnet/s and electromagnet within the same core, normally both permanent ...
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Magnetic Field Simulation Software for Particle Physics

I have been trying to use software for modelling a system of magnetic field, but regrettably they do not make the cut. Is there any software that allows the input of specific requirements into a ...
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Does home cooking induction stove produces any harmful (to humans) electrical/magnetic fields?

An induction cooker, or stove that are based on the principle of electromagnetic induction, and is used much, for cooking food now a days. My stove had a thick iron circular plate on the top. Assuming ...
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How to compute the field lines of an induced magnetic field inside a capacitor?

Consider a capacitor with a varying voltage applied to it. As the voltage changes over time, the electrical field $\vec{E}$ inside the plates does too. Assumption We assume that the direction of $\...
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56 views

Will a electron be accelerated when it move along the non-uniform magnetic field?

For the case that the magnetic field changing with time (i.e., $\frac{\partial{B}}{\partial{t}} \neq 0$), the vortex electric field will be created as a result of the change of the magnetic flux. If ...
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Is it a mistake?: a changing electric field creates a magnetic field

I found here, it says "Ampere's Law roughly states that 'a changing electric field creates a magnetic field'. (It does even have a \cite) Even if it says "roughly states" think this is ...
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1answer
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On not counting initial energy in cyclotrons

The formula for finding the final kinetic energy of a particle exiting a cyclotron is $2nqV$, where q's the charge, V the potential, and n the number of rotations. If the particle starts from exactly ...
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87 views

Could light erase a hard drive?

I have been having a theoretical discussion with a colleague at work. He proposed the idea of a laser being able to erase a hard drive. I know that a hard drive is basically a magnetic disc that can ...
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43 views

Is the curl of this electric field zero and is ampere law true?

let's consider this couple of endless conductive cones connected to an AC voltage source: As shown in the picture, it generates an electric field on circumferences along $\theta$, and a magnetic ...
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49 views

Is there a circulating $E$ field when a single straight wire cuts a magnetic field?

I am a little confused as to the difference between the Lorentz force and Faraday’s induced emf, specifically in the case of a straight wire moving through a uniform B field. I know the answer is that ...
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Magnetic Field on a toroid [closed]

I was trying to solve a problem in which we need to use the magnetic field B inside a toroid with a wire winding around it, but not around the whole extension of the toroid, like this I know that if ...
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28 views

How small can a particle of iron be and still be magnetic?

Any piece of iron that you can hold in your hand will be attracted to a magnet. I suspect a single atom would not. So is there a lower limit to the size of a particle of iron that would still react to ...
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27 views

How would the field in between two semi-infinite placed next to each other look like?

Suppose two semi-infinite solenoids placed next to each other are separated by a small gap as shown below If the solenoids are identical to each other, What would you expect the field in between the ...
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52 views

Can one explain the attraction of two magnets with Faraday's law?

Supose two ideal magnets, close to each other and both at rest, with a north and a south poles both fixed and well defined. May we admit as well that the total electric charge of both is zero in the ...
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Uniform electric field formation in motional emf induction

Why is the electric field $E$ across the ends of a conducting rod, when it's moved with a uniform velocity $v$ in a magnetic field $B$, uniform? Wouldn't it vary non-linearly, since there are opposite ...
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65 views

Induced current in a closed loop in opposing directions

When a magnetic field is given to the loop as in the figure(sorry for the horrible drawing); I'm told that there will be an anticlockwise current induced in both the 'inner' and 'outer' loops, ...
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30 views

Potential energy change in a cyclotron

Every source I've referred to elaborates on the 'energy of the particle' in a cyclotron to have increased by the time it exits, as it's been accelerated multiple times by an electric field. It is the ...
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Depth of a magnetization within a magnetically permeable sample

What model can you use/assume to determine the depth that a magnetic field will penetrate within a magnetically permeable object? Here is the example I am considering - assume a DC field of $H$ ...
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69 views

How does too much current 'kill' a type-2 superconductor?

I recently saw this post: Can a superconducting wire conduct unlimited current? One of the responses mentioned the Meissner effect. However, I am aware that this occurs primarily in type-1 ...
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What is 'in-plane' and 'out-of-plane' magnetization in anisotropic magnets?

Can someone explain what 'in-plane' and 'out-of-plane' magnetization refers to in anisotropic magnets?
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37 views

Amperian loop and magnetic field

Suppose I have a long solenoid with $n$ turns per unit length. The current through the solenoid is changing and I am interested in finding the magnetic field $(B)$ inside. So, we choose an amperian ...
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1answer
30 views

How fast can we spin a large-diameter ring levitated by a well-designed and uniform magnetic field before running up against the laws of physics?

Assume that air-friction can be ignored. Assume that magnetic levitation supports the spinning ring so that hoop stress in the ring is not a limiting factor. Assume that "large-diameter" ...
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How is a current induced in this translating wire?

I am familiar with the principles of electromagnetic induction, but I am stuck on the scenario below: a long straight wire is translating in a uniform magnetic field. According to my book, this causes ...
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28 views

Newton's 3rd Law Coil in Magnetic Field

When a current-carrying rectangular loop is placed in a magnetic field, the forces acting on either side of the loop which is perpendicular to the field provides a torque which rotates the loop. ...
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How to calculate the repulsive strength (weight) of a magnet given gap between the magnet and a base?

When buying neodymium magnets you are typically given a “holding force” value of the magnet in pounds. They even have a nice calculator for determining holding strength given dimensions of the magnet. ...
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27 views

Vector potential for an inhomogeneous magnetic field

I know that you can obtain the magnetic field vector via $\vec{B} = \nabla \times \vec{A}$, i.e.: $$B_x = \frac{\partial A_z}{\partial y} - \frac{\partial A_y}{\partial z} \\ B_y = \frac{\partial A_x}{...
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128 views

Can a gravitational field be focused like a magnetic field?

A pyramidal magnet will focus a greater magnetic field at the top of the pyramid than at the bottom. See video here Is there any evidence that the same holds for a gravitational field? Perhaps the ...
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65 views

How did magnets first come about?

Physics concepts state that in order to turn ferrous (or other magnetic) material magnetic, you need to stroke it with a magnet. Okay, but for the first magnet, we didn't have another magnet to stroke ...
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36 views

At a specific point in a magnetic field, how can there be a direction if there is no magnitude?

I am taught that there is no magnetic force on a moving charge if the charge moves along the direction of the magnetic field. That would mean that the magnitude of the magnetic field at that point ...
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38 views

Which are causes and effects in $D$, $E$, $B$, $H$ fields?

in my book (I'm not putting the reference here since it's not in english) of electromagnetic fields, the following statement is reported about $\vec{E},\vec{D},\vec{B},\vec{H}$ fields: We will assume ...
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36 views

Right Hand Rule Help: Part 2

I’m confused about this problem with the right hand rule. According the book: My thumb should point up (as expected) My fingers should point into the page (I don’t know how that would work) My palm ...
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1answer
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Galilean invariance in Electromagnetism

Griffith's Introduction to Electrodynamics when introducing Faraday's Law, considers two scenarios: Moving loop on a magnetic field. Current flows due to the motional EMF. The same scenario but on ...
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Right Hand Rule Help: Part 1

I thought I understood the right hand rule but I guess not. Here is how I learned it in regards to finding the direction of the magnetic field vector of a current carrying wire. Point your thumb in ...
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How mass (a magnet) affects magnetic force?

I'm here asking this as a student. Magnetic force can be effected by distance, the longer the distance, the weaker, the shorter the stronger. But does mass also effect magnetic force? Does a heavier ...
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110 views

Why is the magnetic field $B$ a pseudo-vector?

Physically speaking, "pseudo-vectors" are vectors $v\in \mathbb{R}^3$ which transform as $ v'= (\det {R})v$ if the "system were to transform as $R\in O(3)$". However, what does ...
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Magnetic Vector potential and it's boundary conditions

The boundary condition for magnetic field B is: $\mathbf B_{above} - \mathbf B_{below}$ = $\mu_0(\mathbf K $ x $\hat n$) But from this, how do we get the boundary conditions for vector potential A ...
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51 views

What is the motion of two charges constrained by a bar in a magnetic field?

Suppose that you have a rod in a uniform magnetic field $B$. The field points in the $z$ direction, while the rod is initially perpendicular to it. At the two ends of the rod, two point-like charges ...
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How to measure critical current of a superconducting wire, if my current source can only supply a small current?

I need to determine the critical current of an aluminum wire at 0.1Kelvin. I have access to dilution fridges, but I cannot modify the wiring in the system from room temperature to the sample space. ...
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Which of these magnets should have the strongest strength at 10cm?

Basically, I need to generate the strongest possible field at 10 cm from a circular magnet, in its central axis. I hesitate about what buying. For example, the following magnet has a large diameter of ...

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