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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Can we interpret timelike, rest frame motion as velocity in the time direction? If so, does it cause charge to generate a ''$B$ field'' perp. to time?

For background: I've had courses on SR/GR from Hartle, E&M from Griffiths/Purcell, and know E/B fields are unified/transform with lorentz boost. My question is less about 'does SR account for E/B ...
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Charge in crossed E and B-fields

This post describes the motion of a charge in crossed electric and magnetic fields as: $$ x = r \cos ωt + \dfrac EB t\\ y = r \sin ωt\\ $$ Can you please explain how these equations are derived. Why ...
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Are these two approaches to the Zeeman effect equivalent?

Consider the unperturbed Dirac equation for a single electron bound to a nucleus with a potential energy $V(r)$: $$ \left[ -i\boldsymbol{\alpha} \cdot \nabla + \beta m_{\text{e}} + V(r) \right] \psi(\...
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How to apply the Bloch-Floquet theorem for a square lattice in a magnetic field?

Generalizing the question here, if I have a square lattice in the homogeneous magnetic field $B$ as the given picture, how can we apply the Bloch-Floquet theorem in this periodic structures (with the ...
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When considering two perpendicular forces how do u know where to measure the angle between resultant force?

For example in these two pictures below ?
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Does induced current lag induced emf in mutual induction?

In a circuit with an alternating emf source, resistor and inductor, the current lags the induced emf on the inductor because the inductor initially opposes a change in current. Now, consider a circuit ...
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For a given $B$ magnetic flux density in a homogeneous magnetic field what is the separation distance between the flux lines?

For a given $B$ magnetic flux density thus number of lines of force passing through per unit of surface area of a homogeneous magnetic field of parallel flux lines inside a vacuum environment, is ...
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How to derive the formula: $F = q\,v\,B\sin\theta\:$? [closed]

How to derive the formula: $$ F = q\,v\,B\sin\theta \tag{01}\label{01} $$ where $\:\theta\:$ is the angle between vectors $\:\boldsymbol\upsilon\:$ and $\:\mathbf B\:$?
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Application of Lenz's law to ideal transformer: how is there a magnetic flux within the iron core?

In an ideal transformer such as the one depicted below (switch is open), a sinusoidally changing magnetic field will be created by the primary coil. However, according to Lenz's law, this sinusoidally ...
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A square lattice in a homogeneous magnetic field B: How would it be the direction of the magnetic potential $A$ in the given picture?

I have an infinite square lattice that is placed in a homogenous magnetic field $B$ with vector potential $A$. My Question Can someone please explain/illustrate how it would be the direction and ...
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Biot-Savart equation not behaving as expected [closed]

I am currently in the process making a large electromagnet with a permeable core that has the following specs: I = 250A N = 300 L = 0.25m relative permability of core = 230000 $B=\frac{\mu_r \mu_0 ...
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Static opened magnetic field line

In every EM textbook, it is written that static magnetic field lines cannot be opened. As an example, one is shown the field lines of a magnet bar where the central field line is obviously straight ...
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Hysteresis Curve of a Super Conductor

Recently I have been studying magnetostatics. I came across the hysteresis curve for various objects such as transformer, a permanent magnet and other materials. Basically these curves tell how good ...
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Does the force between two magnetic poles ever reach zero?

If we hold two magnetic like-poles together and start to move them away, would the repelling force reach absolute zero at certain point? In that scenario, as a layman, I think that there is something ...
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If magnetic field is a bivector, then what is the pole strength?

I have an intuition that magnetic fields are bivectors. While trying to derive some equations with bivectors, I arrived at this formula $$F=\frac{q_{m_a}q_{m_b}}{r^2}\hat r$$ So we have, $$F=q_mB$$ ...
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Faraday Rotation and Elliptical Polarization of Light

I have a question about Faraday Rotation. I read that propagation via the ionosphere results in elliptical polarization, so I did some further research and found that light is made up of right and ...
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Symmetry of line integral of $B$ over circle at infinity with finite number of wires cross plane perpendicularly

I am studying problems which look like this: Some number of wires perpendicular to plane, some line segment (here x-axis is taken), find integral along line segment (here x-axis) In answer to the ...
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Magnitude of Electromagnetic fields are radially symmetric but not direction

Suppose we have a plane and a wire with current passing perpendicular to it. If we consider magnitude field of any point at a perpendicular distance $r$ from the wire, we have the following expression ...
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Does this situation violate Newton's third law? How? [duplicate]

Consider the following setup: We have an infinitely long current carrying wire placed on the X-axis. At some 'x' distance from it is another current carrying wire of length l and it is perpendicular ...
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Why force on small wire is not same as force on infinite wire due to magnetic field?

Question:- Find magnetic force between wires as shown in figure. The infinte wire with current 'I' and the small finite wire of length 'l' with current 'i' at a distance of x from infinte wire (...
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Relative angle of magnetic fields in DC Motor

I'm building my own generator. What is the ideal angle between the magnetic field of the stator in relation to the induced magnetic field of the rotor? Is there a formula to calculate it? For some ...
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Is it better to spread the coil to maximize magnetic strength in air gap of a C shape iron core

See the 2 example below of a C shape Iron Core 99.8% iron. in both cases, assume that: the wire length is the same, say 1000 feet of copper wire. The amp being used is the same The N turns are the ...
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How do alpha particles heat the plasma in tokamaks and what does that trajectory look like?

In a tokamak, a toroid with toroidal and poloidal magnetic fields, Deuterium and Tritium (D-T) fuse at ~10 keV to produce an alpha particle (3.5 MeV) and neutron (14.1 MeV). The magnetic fields ...
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How to calculate Tesla value at the end of a solenoid when iron surface expands?

assumptions: The core and top cylinder are made of pure iron 99.8% with a permeability ( µ ). To calculate the Tesla value at point B (at then end of the solenoid), we use: $$B =\frac{\mu\cdot N\cdot ...
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Making a Permanent Magnet

My understanding is that to make a permanent magnet, a ferromagnetic material is placed in an external magnetic field until its internal magnetic domains (or enough of them) align with the external ...
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How is the heading of an aerial vehicle obtained when given the magnetic field in three dimensions?

An inertial measurement unit (IMU) measures acceleration, angular rates, and magnetic field in three dimensions. I don't fully understand how to interpret the values for the magnetic field and how ...
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Is it right assume the greater the precession of a type of particle in the same magnetic field the slower the particle spin?

Is it right that the greater the Larmor frequency of a particle measured for same magnetic field applied the slower a particle spin is? I read these articles http://hyperphysics.phy-astr.gsu.edu/hbase/...
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Understanding the symmetry argument in determining induced electric fields

I am trying to understand how to determine the shape and direction of the electric fields induced by a changing magnetic field. But all of the resources I have read make use of the following symmetry ...
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29 votes
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Why are magnetic field lines imaginary?

There are many sources online which say that magnetic field lines are imaginary such as Toppr, Vedantu and CBSE Academic. I do know that magnetic fields are real and do exist. But when can we see ...
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What is the shape of the loops of an ideal solenoid?

With a real solenoid made up of circular loops, it can be seen that the magnetic field lines curve around the ends. The curving effect would be less for a rectangular geometry. But an ideal solenoid ...
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Magnetic field lines of a hollow rod with current

Suppose that a long hollow rod has current flowing through it along the length of the rod. I am trying to solve a problem which has such an arrangement of current. The problem manual states that the ...
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2 answers
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Where does the Biot-Savart law contain information about the direction of the magnetic field?

The following image is from Halliday and Resnick, Fundamentals of Physics. The magnetic field at P due to the current element is shown as being directed into the page. The textbook and other sources ...
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Magnetic field during inductor switch-off

I have a question regarding an inductor and the magnetic field when you close the circuit. When I am asking: "How do I get a reverse potential over the inductor when you closed a switch?" ...
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Is there a difference in Earth's magnetic field between day and night?

Is there a difference in Earth's magnetic field between day and night? Magnetic Field
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2 votes
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Are magnetic fields additive?

When considering the field around a permanent magnet or current carrying wire, would it be accurate to say the magnetic field effects of each element add linearly in space, or is the interaction ...
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Is mass spectrometry convenient to separate elements in a mixture?

Are particle accelerators coupled to spectrometers ever used to separate and extract different components of a mixture? If so, how much substance can be treated per day in this way? Would it be a ...
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What is ohmic decay and why does it happen in magnetized celestial bodies like stars and pulsars?

I've seen term "ohmic decay" mentioned in several papers (example) regarding the decay of magnetic fields in celestial bodies like planets, stars, and pulsars, but I can't seem find a clear ...
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6 votes
3 answers
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Suspicious EMF equation

Some context: I am trying to get the equation of motion for a dipole magnet falling through copper pipe. To proceed I need to calculate the EMF. We can do this by using Faraday's law, $$\oint_{\...
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1 vote
1 answer
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Two hollow magnetic spheres, one slightly smaller inside it same polarity facing each other

If you have a magnet the shape of a sphere (hollow) and a slightly smaller magnetic sphere inside it (same polarity facing each other) Will the inside sphere "float" inside the larger sphere?...
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Non-zero electric field in an isolated conductor

I recently came across a problem in which a conducting rod was moving with constant velocity in a constant magnetic field, arrangement is such that rod, velocity, magnetic field are mutually ...
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Calculation of magnet rotation time

Suppose I have the permanent magnet A,and B is an electromagnet interface,that means he can change his poles,and if its pole was the same as the pole of magnet A,the magnet will rotate to the opposite ...
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Frequency of particle in magnetic field

For motion in uniform magnetic field we have 2 parameters that give us trajectory. Radius and frequency. Formulas for them are: \begin{equation} r = \frac{p_{\perp}}{0.3B\cdot e} \end{equation} Where $...
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3 votes
1 answer
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Magnetic field by a electron

In an atom there are $n$ electrons and the $n$th electron creates a magnetic field, as it has velocity and the other $n-1$ electrons will be affected by this force. But still, why aren't we ...
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How does the inner diameter of a copper pipe affect the time taken for a niodynamium magnet to drop through it?

Does anyone know the step by step equations to find out this question?
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How can I calculate the energy stored in some magnets that want to repeal each other? [duplicate]

I have a question. If I have two or more magnets in a way that they repeal each other, how do I calculate the potential energy when compressed? Or maybe, can I know the elastic constant?
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9 votes
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On a magnetar, which force would exert a bigger pull on a 10 kg iron chunk?

On the surface of a magnetar, what would pull harder on a 10 kg piece of iron, the gravity or the magnetic field?
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Proton spin precession and alignment to magnetic field in NMR

Precession due to magnetic field occurs when the magnetic moment of a small coil is proportional to its angular momentum ($\vec{m}=g\vec{L}$). This is due to Euler momentum equation, which for such a ...
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Magnetic Field at a point in the plane of a current carrying ring

I wanted to know how exactly we would approach this problem, i.e. how we could find magnetic field at a point in the plane of a current carrying ring both within the radius and outside. Since Ampere's ...
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Electromagnet attracting permanent magnet?

Permanent magnet gets attracted to electromagnets iron core ,but if we energize electromagnet for attraction force will it attract strongly?
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Is there an electric field due to a neutral current carrying wire?

Consider an electrically neutral wire carrying a uniform current $I$ driven by a dc battery. It definitely produces a magnetic field at points around the wire which we can calculate using the Biot-...
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