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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1answer
28 views

Force of electromagnet on a wire [on hold]

I'm trying to produce an equation for the force produced by an electromagnet on a wire. I'm very aware I don't know any vector calculus but I think as it's the special case (Perpendicular) I can just ...
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11 views

Off-axial Field of Finite Solenoid

Regarding the computation of the off-axial field of a finite solenoid: The Radial and Z components of the off-axial magnetic field of a solenoid are given as: \begin{align} B_r &= \frac{\mu ...
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2answers
52 views

Concept of a Magnetic Field

I was reading a physics book by some author and I got a little too confused with the explanation he stated about magnetic fields. A magnetic field is a field of force produced by current-carrying ...
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1answer
37 views

Fringing effect of electric current

We know the what is the fringing effect of electric field in capacitor, of magnetic field in some in some solenoid or magnetic field in through joint of some metal. But is there is something similar ...
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24 views

A magnet floating due to Meissner effect

If a magnet is floating due to the Meissner effect, can the magnet rotate freely under influence of external field in spite of the presence of north and south pole in it ?
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17 views

surface current density

Surface current density, K is defined as: K = σv where σ is surface charge density and v is velocity. Given a uniformly charged spherical shell with radius R, spinning at constant angular velocity ω, ...
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47 views

$E$-field from changing current in straight wire

A very long insulated wire oriented along the $z$ axis of a cylindrical coordinate system is carrying current that is defined by the following function: $$I(t) =Io + k⋅t$$ (current increases linearly ...
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39 views

Regarding Ampere's Circuital Law

If I am to show that Ampere's Circuital law holds true for any arbitrary closed loop in a plane normal to the straight wire, with its validity already established for the closed loop being a circle of ...
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0answers
16 views

Rotating uniformly magnetized sphere [closed]

Suppose a uniformly magnetized conducting sphere of radius $a$ so : $$M=mH(a-r)\hat{z} $$ where $m$ is a constant and $H(r)$ is the Heaviside function. This is a classic problem in magnetostatics. ...
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1answer
15 views

$H$ field from corresponding $E$ field (antenna)

The $E$ field at $kr >> 1$ due to a short dipole oriented in the $z$-direction and located at the origin is: $$E_0 = \frac{10^3e^{-jkr}}{r}\sin\theta\space\space(V/m)$$ Can I just solve for the ...
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1answer
24 views

Dependence of Hall coefficient on temperature in copper

As part of a project on the Hall Effect in metals, we would like to find out whether the Hall Coefficient of copper depends on its temperature, and if so how. We passed a current I through a copper ...
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2answers
76 views

What is the secret of this perpetual motion machine with neodimimum magnets?

The following device is apparently based on magnetic forces only and has no visible energy source: Where is it's energy source? Full video: http://www.youtube.com/watch?v=eA0b-8pqUCk UPDATE One ...
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42 views

Adding Magnetic Fields?

Ok, so we all know that the strength of a magnetic field can be increased if a wire with current flowing through it is surrounding the magnet. Because the current flowing through the wire is making a ...
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2answers
55 views

Magnet dimensions for 3-phase permanent generator

I'm making a 3-phase permenant generator. According to Faraday's law, the emf produced is negative number of turns times the change in magnetic flux over the change in time. If it is only the CHANGE ...
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2answers
62 views

Particle beam in infinite magnetic field

In a physics exam at university I had the following problem: A proton-deuteron beam is accelerated by a $\Delta V = 10^7\,\mathrm{V}$ difference of potential. At some point, the particles enter ...
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27 views

Anomalies in weighing a magnet [duplicate]

In weighing a strong magnet there is a difference in weight when the magnet is weighed from different polarization directions. The differences in weight are not due to polarization because ...
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0answers
26 views

Magnetic levitation project

For the past four years, I have been working on a project that will allow permanent magnets to levitate stably above a magnetic surface. So far I have tested my first theory which was to see if ...
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1answer
45 views

Is the Biot Savart Law applicable only for continuous currents?

There is a widely known formula for the magnetic field due to a moving charged particle. $$\frac{\mu_0}{4\pi} q \frac{\vec{v}\times\vec{r}}{r^3} $$ The usual derivation is as follows. $$ dB = ...
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1answer
26 views

why induced emf in primary coil is only caused from self inductance but not mutual inductace

A is primary coil and C is secondary coil A is connect to a battery while there is no source connected to C When the current in A varies with rate $\frac{di_0}{dt}$ there is induced emf in B that ...
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1answer
38 views

Simple question with magnetic fields

On my test of today was the following question: "an aluminium block moves with a constant speed over a road, ahead of it is a magnetic field. Does the speed change when it enters the magnetic ...
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20 views

Quantum Locking Inverted

I have recently been investigating the phenomenon known as "quantum locking". I have many questions about the engineering aspects of this phenomenon such as what range it operates, what shapes can be ...
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1answer
26 views

Electricity on magnetic powder

I had the idea of, what if you ground up some magnets into a fine powder, what would happen with the powered, and how would it act? After some google searches, it seems that this isn't done very ...
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0answers
10 views

Analytical Calculations For a Stable Electret in Motion in Interplanetary Space. Determining the magnetic field

We know that a charging capacitor has, associated with the increasing E-field, a magnetic field. Now please consider the case of a very strong dipole or E field produced in an electret. Let us say ...
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0answers
11 views

How to calculate magnetic flux density in gap

I have the following setup (where the relative permeability of the ring is $\mu_{r}$): I am struggling to work out how to calculate the magnetic flux density $\vec{B}$ in the gap in the ...
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0answers
30 views

Ampere's law and magnetic circuit

For magnetic circuit there is an equation NI=HL. This equation is obtained by applying Ampere's law. H is magnetic field intensity and L is the length of the circuit. In following picture the equation ...
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0answers
14 views

$H$ field in Faraday's law problem?

In my textbook it says, Consider a rectangular loop in the vicinity of an infinitely long wire carrying a current $I(t)$. To calculate the magnetic field, we can use the quasistatic approach, which ...
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0answers
37 views

Torque on a wire loop from straight wire [closed]

I need to show that the torque on this wire loop is $$N = \frac{\mu_0}{\pi} 2abdII' \frac{(b^2+d^2)\sin(\theta)}{b^4+d^4-2b^2d^2\cos(2\theta)}$$ The where $\theta$, is the angle between the loop ...
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1answer
56 views

Calculating electric field using a given magnetic field equation (Maxwell-Faraday law)

The following magnetic field is given (and nothing else is known): $$ \begin{cases} B_0 \frac{t}{T} & \quad\quad\quad r < R \\ 0 & \quad\quad\quad r > R \end{cases} $$ I need to ...
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2answers
72 views

Do transformers lose energy?

EDIT: The title should rather be how/why transformers lose energy My idea of a transformer is that it is composed of two separate wire windings around some metal core. The purpose is to ...
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4answers
40 views

How do magnetic field lines cancel outside of a solenoid?

Please explain me briefly, how magnetic field lines cancel outside solenoid? There is only one wire wrapping it and therefore only one direction of current so how can magnetic field cancel out? How ...
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0answers
8 views

What cause the variation of inductance in inductor having ferromagnetic core?

If the core is ferromagnetic then the permeability vary as the increase of flux density or magnetic field strength cause by the increase of current and so the inductance can vary as $$L=\mu_0\mu_r ...
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0answers
22 views

Conductors - force needed to maintain a constant velocity

There runs a current $I_0$ through a straight and long conductor. Two more conductors are placed parallel to it in a plane with distances a and b respectively. The resistance of the connection is ...
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1answer
102 views

NOT Perpetual Motion; Could It Work?

TL;DR The energy is not being created freely, so why shouldn't it work? We have all seen the YouTube "perpetual motion" machines. You know, the computer fans with magnets taped on them and hidden 9 ...
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0answers
29 views

Flux cutting in a uniform magnetic field

Say we have a uniform magnetic field acting into the page, and we have a bicycle wheel which is spinning at a constant tangential velocity $v$. Each spoke has a equal length, $l$. Reading has told me ...
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31 views

Magnetic forces [closed]

Can we generate magnetic field forces for pushing or pulling devices? How much weight can be pulled by electromagnetic field?
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2answers
25 views

Change of magnetic flux on size of magnetic field and area

Consider a solenoid with 50 turns. Each turn gives has an area $A$. When the power is switched on, each turn produces a magnetic field of 1 Tesla. What is the total change in magnetic flux when the ...
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2answers
34 views

If I double the amount of oxygen molecules, do I double the paramagnetic force?

Oxygen is well known to be paramagnetic. If I take one molecule, $O_2$, and measure its paramagnetic force due to externally applied magnetic field, and then add another molecule near the first ...
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0answers
18 views

The magnetic field strength/intensity produced by the coil is always $\frac{NI}{l}$?

By comparison between electric field and magnetic field. The relationship between H and B is analogous to E-D relationship that $$B=\frac{H}{\mu_0}$$ as same as $$D=\frac{E}{\epsilon_0}$$ However ...
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0answers
21 views

Does a magnet floating over a superconductor slowly fall and take infinite time to stabilize?

The reasoning being that as the magnet moves towards the superconductor it induces an opposite magnetic field, until the latter rises sufficiently to equal the weight of the magnet. Except that looks ...
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0answers
99 views

Confused on how to apply the volume integral form of the Biot-Savart law

In Viscous evolution of point vortex equilibria (Jing, 2011) the author explains that the velocity equation for the Lamb-Oseen vortex is found by applying the 2D Biot-Savart law to the vorticity ...
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1answer
23 views

Does the wireless energy tranmission affect compass

Wireless energy using magnetic inductive coupling. So magnetic field will be affect around device. We use it to charge mobile device so I wonder if it will affect compass in our device
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2answers
33 views

Equation of a Magnetic Flux Line

I have a simple problem that I am not quite sure how approach: Consider a spatially nonuniform magnetostatic field expressed in terms of a Cartesian coordinate system by $\textbf{B}(x,z) = ...
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0answers
29 views

Longitudinal Adiabatic Invariant in Magnetic Mirror

I am trying to solve the following problem from Bittencourt's Fundamentals of Plasma Physics (Problem 3.4). I have posted an attempted solution below the problem statement: Consider a system of ...
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2answers
59 views

What are diamagnets and paramagnets?

A paragraph in my text reads: An atom or ion with all electrons paired is not attracted by strong magnets and is termed 'diamagnetic'. In contrast, spins do not cancel when unpaired electrons are ...
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18 views

Wire loop in the magnetic field

I have strange problem, and no idea how to solve it. The wire loop $ ABCD $ is in a magnetic field of the long thin rod magnet with a magnetic moment per unit volume of $\mathfrak{M} _0 $ and a ...
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1answer
18 views

understanding shceme field lines - magnetic field

I would like to know if the magnetic field is in "the x-y plane". Does this mean the field lines are actually parallel to the visible line x or y? Or does it mean the field lines are parallel to the ...
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0answers
25 views

Lifting capacity of superconductors

How does the strength of the magnetic field the superconductor is exposed to affect its ability to levitate/lock heavier objects? Or is there no relationship (for superconductors) between magnetic ...
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0answers
18 views

Nuclear powered flux compression generator?

A flux compression generator is a device for converting the chemical energy of explosives into magnetic field energy, with reported efficiencies of up to 20%. Is there a limit on the conversion ...
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0answers
15 views

Electric potential at the wings of a plane

PROBLEM: A plane with wing span 70 meters is flying with a speed of 100 m/s in a uniform magnetic field B = 5 T that is directed vertically with respect to the wingspan. What is the emf produced ...
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24 views

What is strength of an electromagnet at a distance?

I want to levitate a permanent magnet between two electromagnets. My two governing equations are: $$F = \frac{B^{2}A}{{2\mu_{0}}}\tag{1}$$ $$B = \frac{NI\mu}{L}\tag{2}$$ Where $x$ is the distance ...