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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 [tag:magnetism], as questions about the phenomenon & theory of magnetism do not necessarily involve the discussion of ...

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Torque lesson in Physics

For the force on a current-carrying wire, Torque, was derived using the assumption that the cross-section area of the wire is constant along its length. Is this equation still valid if the cross-...
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2answers
16 views

Magnetic field and magnetic forces and polarity

When the polarity of the voltage applied to a dc motor is reversed, the direction of motion does not reversed. Why not? How could the direction of motion be reversed?
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Magnetic field and magnetic forces

Hall-effect voltages are muchh larger for relatively poor conductors (such as germanium) than for good conductors (such as copper), for compatible currents, fields, and dimensions. Why?
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Creating magnetic field

I read this article yesterday about creating super strong magnetic fields with lasers https://physicsworld.com/a/radiation-friction-could-make-huge-magnetic-fields-with-lasers/ But was disappointed ...
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liquid metal induced current due to rotation in B field

My question is this, I have a hard time figuring out the outcome due to the geometry I assume. So I have a rotor, on the rotor sits a ring filled with conductive liquid metal, also on the rotor there ...
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2answers
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Why is the magnetic field strongest at the poles in a permanent magnet?

In a solenoid, the field lines within are relatively constant and parallel, and so, the magnetic field is strongest as compared to the poles, at which the field lines diverge. In a permanent magnet, ...
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44 views

Magnetic forces in physics

Could an accelerator be built in which all forces on the particles, for steering and for increasing speed, are magnetic forces? Why or Why not?
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25 views

Magnetic force and field involving simple harmonic motion

Is there a simple harmonic motion when the electromagnetic compass was made by suspending a coil. The coil align itself perpendicular to the horizontal components of the earth's magnetic field and ...
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14 views

Can electromagnetic radiation affect the ability to navigate using magnetic field of Earth?

Recently I came several articles how Electromagnetic Radiation (EMR) is leading to a decline in the population of bees and birds. The important point being emphasised is that EMR affects their ...
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Is there a limit on the magnetic field in a Hall generator?

In a Hall generator, charge accumulation on electrodes occurs because there is a generated current, $\bf{J}$, in a magnetic field, $\bf{B}$. This results in charge separation due to a Hall current ...
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Simple harmonic motion in physics [on hold]

When can you say that an electromagnetic compass is experiencing simple harmonic motion?
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1answer
30 views

How to generate a very steep magnetic field gradient

I am a student that's very new to magnetism in general and I've been reading/learning for the past few weeks. I'd like to build magnetic tweezers to use in materials with kPa order stiffness - so I ...
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A multiple choice question on magnetic fields and magnetic force [on hold]

On the two vertices B,C of an equilateral triangle ABC of side d on a very rough horizontal surface, two ants of negligible dimensions start in such a way that ant from C always moves with constant ...
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Direction of force in a magnetic field [on hold]

The main question is: In a region of space exists a uniform magnetic field that is directed towards the negative sense of the Z axis. Indicate the direction and sense of the force that acts over the ...
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1answer
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Magnetic force and field [on hold]

a student tried to make an electromagnetic compass  by suspending a coil or wire from a thread (with the plane of the coil vertical) and passing the current through it. she expected the coil to ...
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3answers
42 views

Understanding when magnetic fields are produced

We all understand that moving charges create uniform magnetic fields. Saying this, if we consider the example of a neutral current carrying wire, then there is a uniform magnetic field around it. My ...
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Why are magnetics fields recorded by MEGs (magnetoencephalograms) not distorted by the scalp?

My question "Why are magnetics fields recorded by MEGs (magnetoencephalograms) not distorted by the scalp?" arose when I was reading about MEGs in Quantitative EEG, Event-Related Potentials and ...
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1answer
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Does a magnet lose more potential when (passivley) magnetizing another metal?

Does a magnet lose more of it's magnetic potential when (passively) magnetizing a second (ferromagnetic) metal compared with simply being left alone for the same amount of time it took?
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Do non-ferromagnetic materials diminish magnetic fields?

This question talks about the effect of a ferromagnetic iron bar that changes the magnetic field of a permanent magnet in it's vicinity. I'm wondering if this effect is also present for non-...
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2answers
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What is the speed of the magnetic field?

There is an invisible magnetic field that pushes apart two repelling magnets What is the speed of that magnetic field?
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Increase in the strength of a magnetic field in synchrotrons

I have a very simple question I'm working on a small project, and I worked out sometime that I can't seem to verify online Basically, I'm trying to find how the magnetic field strength inside a ...
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Line integral of a closed loop magnetic field [closed]

So I know that line integral around just a normal wire with current flowing is given by Ampere's Law where the closed loop integral of the dot product of magnetic field and the derivative of the ...
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2answers
189 views

An electron moving through a magnetic field [closed]

An electron, that has been accelerated from rest by a potential difference of $250\ \rm V$, enters a region of magnetic field of strength $0.12\ \rm T$. Show that speed of the electron after ...
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1answer
18 views

Magnetic force comparison

Two magnets of different size are tied on two sides of a wall with non-elastic rope on a horizontal surface and the opposite poles face each other. Why is the tension on both of the ropes the same? ...
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1answer
18 views

What is the EMF in a bar rotating around any point?

The problem of a bar (or rod) of length $l$ rotating around one of its ends in a magnetic field of magnitude $B$ is very well known. The induced emf is $\frac{1}{2}B\omega l^2$, where $\omega$ is the ...
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Can magnets be arranged to interact with earths magnetic field to produce force?

Is it possible to arrange one or more magnets along with iron/ferric guides to interact with our planets magnetic field in such a way that a force is generated in one or more directions? Would a ...
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2answers
43 views

Magnetic force under change of reference: Do Maxwell's equations hold?

Suppose I have a uniform magnetic field through all of space $$\textbf{B}(x,y,z)=\hat{\textbf{z}}$$ and a charge $q$ moving at a velocity of $v\hat{\textbf{x}}$. In this frame of reference, a magnetic ...
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Switching off AC current supplied to RF coil on atoms instantly

Imagine if you have an ensemble of cold atoms aligned parallel to a large field along z direction. Then, I apply a magnetic field of the form $A\cos(\omega_{rf} t)$ transverse to the spin (created by ...
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1answer
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Calculating the final velocity of a simple electric train, cont [closed]

So I have a school project that I am doing which is basically calculating the final velocity of a simple electric train (aka the battery). I am in grade 12. https://www.youtube.com/watch?v=J9b0J29OzAU ...
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Will the expressions for magnetic vector potential and Biot-Savart law hold at points on line current?

If we have a line current, will magnetic field be defined at points on the line? Will the expressions for: $(1)$ Magnetic vector potential $$\vec{A}=k\int^l_0 \dfrac{\vec{dl}}{r}+\nabla f(x,y,z)$$ $(...
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1answer
37 views

Magnetic field at points on the circuit

I know magnetic field lines due to a circuit always form closed loops. Therefore $\nabla \cdot \vec{B}=0$ everywhere (even at points on the circuit). However due to singularity, magnetic fields are ...
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1answer
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Question about when the Biot-Savart law holds

Is the condition $\dfrac{\partial\textbf{E}}{dt} = \boldsymbol{0}$ sufficient and necessary for the Biot-Savart law to hold? If it's sufficient but not necessary, under what other conditions does the ...
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1answer
29 views

Is the path of a charge in magnetic field uniquely determined by two points?

My questions is as the title suggests, if I know two points a charge passes in a magnetic field, will that correspond to one unique path? I know that a starting point and velocity gives me one unique ...
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10 views

Intensity of magnetic field and magnetic field

If I have a solenoid with a ferromagnetic material In the core, why is magnetic field not the relative permeability of the iron core times the magnetic field intensity? Why does relative permeability ...
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1answer
26 views

Does a magnet always reorient itself along the most efficient path?

If a magnet is held in a magnetic field in which it is not in the position of lowest energy, the magnet will tend to reorient itself to align with the field. When reorienting in 3D space, there are an ...
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How much time does it take magnetization to appear, after turning on a magnetic field?

When a magnetic field ${\bf H}$ is turned on from zero, a piece of material, not previously magnetized, exhibits a magnetization ${\bf M}$ due to ${\bf H}$. According to ${\bf M} = \chi {\bf H}$, ...
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37 views

inverse square law for magnetic field calculation

First of all, let me say that I am very bad at mathematics. If you think I am just being modest, read on for proof! I am trying to ascertain the field strength of a small bunny rabbit fridge magnet, ...
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2answers
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Why do the matrices in k-space and the final MRI image have to match?

Naturally, there is no correspondence pixel-to-pixel between Fourier space (k-space) and the final 2D image of an MRI - k-space stores the Fourier coefficients, hence each pixel in it affects the ...
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1answer
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How does a gradient elicit a RF signal from the stimulated tissue in MRI?

I understand the idea of spatial encoding afforded by the application of a readout gradient along one of the planes (frequency direction) in MRI. In typical 2D image generation, there is also a phase ...
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1answer
46 views

How do magnets move towards or away from each other?(Explanation on a molecular level)

Imagine two magnets on a horizontal surface, with two opposite poles facing each other. If one of them is north, then the other magnet with the south pole facing the north will move towards the north ...
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1answer
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Convert magnetic field from cylindrical to cartesian coordinates

It's been a while since I had to convert cylindrical to cartesian unit vectors, and even though I have the transformation rules, I can't seem to grasp how to go about the following: How would I (what ...
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What equation describes the change of magnetic flux density based on temperature for a cylindrical neodymium magnet?

I have a neodymium magnet which I am subjecting to various temperatures and measuring the change in magnetic flux density using sensors. What is the theoretical formula that models this relationship ...
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1answer
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Is there is any way to prove the Faraday's law of induction?

I want to know if there is any way to prove the Faraday's law or is it just an experimental observed phenomena? More specifically, is there any reason why the proportionality constant is 1? How did ...
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Magnetic field of a rotating superconductor - exists?

On several places (e.g. wikipedia superconductivity) people stay, that for superconductivity the resistance is exactly zero. The mass of electron is small, but for sure not exactly zero. Imagine a ...
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3answers
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How do we deduce the vector potential for a constant magnetic field?

How do we show that for a constant magnetic field $\vec B = const$, the vector potential is $\vec A = \frac12 \vec r \times \vec B$?
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Why not change magnetic flux only at the edges?

I learnt Faraday's Law of Induction however I was confused about why the area aspect of magnetic flux impacts on the EMF generated. Why do magnetic field lines inside the coil area affect the EMF ...
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42 views

Uniqueness of the current loop inverse problem

Imagine we have a circular planar current loop where the current contour is infinitely thin. Free parameters of this loop will be: coordinates of the center; current density $I$ and sign; radius of ...
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Demagnetisation field in infinite, homogeneous body

I'm an elasticity theorist but have recently ended up working with electrical and magnetic fields. This question is simple, and I'm pretty sure I know the (probably obvious) answer, but just wanted to ...
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2answers
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Lagrangian of EM field: Why the $B$-field term has a minus sign in front of it in the Lagrangian?

I know that $L = T - U$ and that, in the non-relativistic case $$L= \frac{1}2mv^2 - q\phi(r,t) + q\vec{v}\cdot\vec{A}(r,t).\tag{1} $$ My lecturer used the following form of the Lagrangian density ...
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Visually and physically reasonable analytic approximation to the field of a bar magnet

I want to produce publication-quality drawings of the field of a bar magnet, in both the field line representation and as a "sea of arrows." I've found some open-source software that looks like it ...