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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187 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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0answers
153 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
259 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
78 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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0answers
48 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
92 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
34 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
45 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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0answers
28 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
63 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
21 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
67 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
91 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
21 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
79 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
132 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
109 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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5answers
533 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
40 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
60 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
138 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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1answer
57 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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0answers
32 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
54 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
102 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
29 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
29 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
176 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
33 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
45 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
59 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 ...
3
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2answers
157 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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0answers
45 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
24 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
61 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 ...
2
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0answers
27 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
30 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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0answers
112 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 ...
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0answers
29 views

Magnetic field along the line which is perpendicular to the wires

Suppose we have 3 wires which cross at some point $A$. After the branching point, the electric currents in two arms are $I$. And we have the line passing through the point $A$ and perpendicular to the ...
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0answers
46 views

understanding magnetic dipole moment and torque [closed]

I would like yo know if I understand things correctly: Magnetic moment, which is a constant value for a solenoid or magnetic dipole, determines the torque it will experience in a magnetic field. (I ...
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1answer
73 views

Magnetic field between two rings [closed]

Two rings are placed parallel atop each other along an axis with a distance $\epsilon$ which is much smaller than the radius of both rings a. Through one of the rings there is a current I and through ...
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0answers
16 views

from control torque to magnetic moment

I am designing a system which generates a magnetic field to make itself move in space (a cubesat with magnetorquers). This magnetic field is known as the magnetic control torque, i.e. it will torque ...
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1answer
61 views

Has the effect of magnetic fields on time ever been examined experimentally?

Relativity of time can be examined with satellites as gravitational or acceleration. Is there any similar experiment with intense magnetic fields?
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4answers
853 views
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0answers
69 views

Why is emf 0 for coil rotating in field?

Say you have a coil (that can carry a current) rotating in the field between two magnets. When the area of the coil is perpendicular to the field lines the emf induced in the coil is 0, why is this?
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2answers
518 views

Magnetic field outside an infinite solenoid

Can someone explain to me how the magnetic field cancels outside a solenoid of infinite length mathematically (using an integration or something)?
4
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1answer
105 views

How long does it take a magnet to lose its magnetization? [duplicate]

As we all know, a magnet has some magnetization that lets it attract other ferromagnetic materials but I was wondering how long it takes to lose this magnetization? Is it even possible or not?
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0answers
16 views

Can a magnet lose its strength over time? Especially when repulsive magnets are around? [duplicate]

I was thinking of hanging delicate art glass pieces separated by opposing magnets on walls simply using the power of magnets. I was wondering will the opposite poles have any effect on the strength of ...
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0answers
84 views

What happens to the magnetic field when the source is turned off?

Suppose you had a magnetic field source in space and a piece of iron a light minute away. Assuming magnetic fields propagate at the speed of light since they are massless, if you turn on the magnetic ...
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2answers
124 views

Does a moving charge have additional (magnetic) energy

My understanding so far: A moving charge produces a magnetic field, B, in an analogous way to a current produces one. A magnetic field has an energy density which is proportional to B squared. My ...