The classical theory of electric and magnetic fields, both in the static and dynamic case. Also covers general questions about magnets, electric attraction/repulsion etc. Distinct from electrical-engineering.

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In a strong field, how long would it take for domains to align?

How fast is the rate of "switch" for the domains to align with an exterior field? Possibly in milliseconds? I assume it won't take much time since domains are very small, and they only turn from a ...
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1answer
79 views

Heating effects of microwaves

I understand the heating effect(dielectric heating) of microwaves. This heating is caused by using a frequency of 2.45 GHz and this is the same frequency at which Bluetooth works and the L and S ...
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2answers
59 views

In calculating resistivity of skin do I use the body's surface area?

Most of the resistance of the human body comes from the skin, as the interior of the body contains aqueous solutions that are good electrical conductors. For dry skin, the resistance between a ...
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2answers
50 views

Condition for the magnetic field

Let $B$ be the magnetic field. If $$\nabla \times B = 0$$ and of course $$\nabla \cdot B= 0$$ Can we conclude that $B=0$? For a general field it is wrong because every constant vector will ...
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0answers
27 views

Is this expression of electric field correct?

I know that the electric field component of electromagnetic wave should be written as the first equation shown, but some times it can be expressed in terms of complex amplitude of electric field as in ...
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0answers
27 views

Magnetic forces and generators

i'm really struggling to break this question down into manageable chunks and identify which quantities are relevant. I'm also unsure of some of the wording in the question. A bar of length ...
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2answers
109 views

How electromagnetic fields travel through vacuum?

How electromagnetic fields travel through vacuum is it right to say that they propagate or travel? do they alternately form each other by charged particles?
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3answers
4k views

Does a current carrying wire produce electric field outside?

In the modern texts of electromagnetism in the presence of stationary currents the electric field is assumed conservative $\nabla \times E =0 $. Using this we get $E_{||}^{out}=E_{||}^{in}$ which ...
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1answer
37 views

Is the charge of a current carrying wire real or hypothetical?

Realist753 Theory Relativistic Electrodynamics assert that a current carrying wire being neutral in a laboratory frame of reference appears electrostatically charged to an observer in relative ...
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1answer
144 views

Electric field from current without Maxwell's law of induction

A long, straight wire carries a current that decreases linearly with time. What is the direction of the induced electric field outside the wire? I would interpret this as follows: A current induces ...
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1answer
56 views

What determines the magnitude of force of an electromagnet?

Let's assume that there is an electromagnet with $B = 1 Tesla$ , what is the magnitude of the force it could generate on other dipoles equal to it's surface area? Can the magnitude of force (in ...
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4answers
2k views

How does inductor store energy in the magnetic field?

I learnt from book that magnetic field does no work because the force is proportional to $\vec{v}\times\vec{B}$ where $\vec{v}$ is the particle velocity. That vector cross product is always at right ...
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3answers
123 views

Integral form of Gauss's law for magnetism from Stokes' theorem?

How can the integral form of Gauss's law for magnetism be described as a version of general Stokes' theorem? How does it follow?
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1answer
188 views

Electromagnetic duality

A key aspect of modern physics is the mapping of theories or different descriptions of a theory into a one-to-one correspondence. As I am trying to further understand the electromagnetic field tensor, ...
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1answer
53 views

Thomson's jumping ring experiment

For the jumping ring experiment (I think it is also called Thomson ring experiment) why does the ring float and not move up and down the ring as would be expected, I think by Lenz's law, since would ...
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1answer
60 views

Force from solenoid

I'd like to approximate the force from a solenoid, or at the very least find a formula which is proportional to the force so that I can experimentally find the constant for my particular case. ...
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2answers
71 views

Lorentz force, must there be two magnets?

The diagram above demonstrates the Lorentz force, Yet I wonder... must there be two magnets/electromagnets? If the two magnets form a magnetic field of $1$ $Tesla$ acting on the wire, why not use 1 ...
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1answer
51 views

Calculting the magnetic field from rectangular conductor?

I want to apply the Biot-Savart law to calculate the magnetic field at a point created by current flowing through a square/rectangular conductor. More specifically, a trace on a printed circuit board. ...
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2answers
54 views

Is there an analogue of a geodesic for the evolution of the electromagnetic field? [duplicate]

For a charged particle moving in free space, we can say from the homogeneity of space-time, that it moves along a geodesic. Is there an analogous principle for the evolution of the electromagnetic ...
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2answers
66 views

Locations of destructive interference for two spherical waves

I have looked at this, but it did not help with locations. Really this just comes down to mathematical manipulation, which for some reason I fail to see. Here is my paraphrased setup: Consider two ...
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1answer
77 views

H field of this magnet?

How can I know the magnetization force that this magnet applies to other ferromagnets? What is H(in Oe or A/m) of this strong magnet? From the site: ...
5
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1answer
68 views

Is it possible to see light intensity fluctuate?

Solutions to Maxwell's equations shows that the $\vec{E}$ and $\vec{H}$ component are of the same phase, which means they go to maximum and zero together, therefore the intensity of the ...
2
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1answer
334 views

Induction and Halbach Array

I have recently studied and tried to understand the concept of the Inductrack ( http://en.wikipedia.org/wiki/Inductrack ), a form a magnetic levitation. In the following link they present three ...
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1answer
20 views

Lamination on a conductor?

How can lamination help reduce eddy currents? I understood that it reduces them, by making their circulation incomplete, or something like that. Can anyone explain this please?
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2answers
634 views

What could magnetic monopoles do that electrically charged particles can't?

I understand the significance to physics, but what can a magnetic monopole be used for assuming we could free them from spin ice and put them to work? What would be a magnetic version of electricity? ...
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3answers
67 views

Inductance of a solenoid?

My textbook is using Faraday's law to explain the self inductance that happens in a solenoid with changing current. According to Wikipedia, Faraday's Law is: The induced electromotive force in ...
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4answers
183 views

What is Electromotive force (EMF)? How is it related to potential difference?

What is Electromotive force (EMF)? How is it related to potential difference? Is it the creation of potential difference in any conductor??Is it a process?Why is it called force?
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3answers
175 views

Can magnetic flux be negative

I am studying magnetic flux linkage in an ac generator and it appears to be that magnetic flux linkage is negative half the time, how can this be?? Also with lenz's law why is emf defined as negative ...
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0answers
39 views

Earth as a conductor and emf produced? [closed]

Since about 73% of total surface of Earth is occupied by water, its internal is also occupied largely by hot molten mass.Let,the whole earth is considered a conductor.Sun is a source of gravitational ...
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1answer
68 views

Issue with running a Van De Graaff generator

I am following this online video: http://www.youtube.com/watch?v=fsT69XnjxgU but my Van De Graaff generator is not working. I am using pvc pipes for the body, nylon and electrical tape as two rollers, ...
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2answers
43 views

Determining the minimum pull force of a magnet required to hold it in place

If I place a magnet on the underside of a metal object so that it is held there by its attraction to the metal, how can I determine the minimum pull force the magnet needs to have in order to keep it ...
2
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1answer
51 views

What happens when you pass a current through a coil made of a ferromagnetic substance?

I know when you pass a current through a length of copper coil or a solenoid, there is the induction of a magnetic flux. But what of the coil made of the ferromagnetic material, the permanent type ...
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2answers
49 views

Electron Electric Field Mass?

I am confused of whether or not the expected electromagnetic field generated by the point-like electric charge of the electron distributed smoothly across space as a probability distribution creates ...
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2answers
763 views

How is the direction of a compass affected by a current in a wire?

If I place a compass over a wire(such that the wire is positioned north-south) with charge flowing through it, and it points northeast, how can I determine the direction of the electron current ...
0
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1answer
72 views

Am I interpreting Gauss' Divergence Theorem correctly

I was reading Introduction to Electrodynamics by Griffiths and I wanted to check if I understood Gauss' Divergence Theorem correctly. The theorem states: $$\int \int \int_V \vec{\nabla} \cdot \vec{C} ...
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1answer
67 views

Maximum potential of a van de graaff generator

I know that we can calculate the maximum potential of a van de graaff generator by ( radius* electric field in which corona discharge begin to form in the surrounding gas( according to wikipedia 30 ...
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2answers
342 views

What is charge actually? How to define it? [closed]

Is charge of something for (e.g.) an electron related to electromagnetic space if it exists due to energy, due to which it may have mass? I don't know about quantum mechanics or advanced particle ...
2
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2answers
87 views

Why is the Faraday Tensor derived from the Lorentz force?

If we start from the Lorentz force, $$\textbf{F}=q\textbf{E} +q\textbf{v}\times\textbf{B}$$ and use the four velocity u$^{\mu}$ and the four momentum p$^{\nu}$, then we get to ...
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2answers
30 views

How to express magnetic field vector in terms of force on current

I am preparing for an exam and one of the questions I have come across asks: Define the electric field $\mathbf{E}$ and the magnetic flux density $\mathbf{B}$, in terms of the force on charges and ...
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1answer
72 views

Is magnetic wheel possible?

I once tried to make a magnetic wheel using different shaped magnets and placing them in different orientations and of different shapes.But it did rotate making a small angle ie it didnt rotate even a ...
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0answers
27 views

What is the symmetry associated with electric charge conservation [duplicate]

Is there a kind of symmetry that yields the conservation of charges? and if so , how it works for both type of charges? Electrical Charges
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3answers
1k views

What is the symmetry which is responsible for preservation/conservation of electrical charges?

Another Noether's theorem question, this time about electrical charge. According to Noether's theorem, all conservation laws originate from invariance of a system to shifts in a certain space. For ...
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5answers
328 views

How would charge distribute if electrons were balls?

In a conductor, any excess charge will distribute itself evenly over the surface of the conductor. Because of quantum mechanics, this is possible with small charges (i.e. 1e). But if electrons were ...
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1answer
49 views

Current through two inductors after a long time

I'm having trouble with visualizing the following problem, which is asking me for the final, steady current in both inductors $L_{1}$ and $L_{2}$. I was thinking that after a long time, essentially ...
0
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1answer
35 views

How does electric current generate thermal energy?

How does free electrons moving through a wire cause random vibrational motion of the positive ions?
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8answers
2k views

Do Maxwell's Equations overdetermine the electric and magnetic fields?

Maxwell's equations specify two vector and two scalar (differential) equations. That implies 8 components in the equations. But between vector fields $\vec{E}=(E_x,E_y,E_z)$ and ...
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2answers
52 views

Maxwell-Faraday Equation and Electric Fields

I have a question regarding, as the title says, this equation: $\nabla \times \textbf{E}=-\frac{\partial \textbf{B}}{\partial{t}}$ So, the above equation says that the curl of an electric field is ...
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0answers
46 views

Four-current, Induced Charge and Magnetic Flux

I'm studying Jackiw's "Fractional Charge and Zero Modes for Planar Systems in a Magnetic Field" DOI: 10.1103/PhysRevD.33.2500 but I have difficulties at some points. One of the problems is $$\langle ...
0
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1answer
455 views

Why magnetic field lines and force are not orthogonal with magnets?

The below explanation why magnetism exists is superb in this video. The explanation about magnets is also great in this video. A magnet has atoms with unpaired electrons forming mini magnets. The ...
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1answer
84 views

In which mathematical space do magnetic fields live in?

A magnetic field may be described as a mapping $\mathbb{R}^3 \to \mathbb{R}^3$. Therefore, it is a function, and apparently can be described as an element in a function space. Is there some particular ...