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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27 views

Can antennas work with high frequency EM waves?

Antennas usually work with FM waves, and AM waves, which mostly used in telecommunications. Information is transferred on FM, and AM waves by a transmitter transmitting information on these EM waves. ...
3
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1answer
194 views

Hearing background noise from earphone while there isn't any connection

Once my friend told me that he was listening some background noise while his earphones were not plugged in any device. I didn't believe him but 10 minutes ago I experimented the same. I can certainly ...
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2answers
735 views

Repelling a weak permanent magnet with an electromagnet

I have a question about magnetic repulsion. Suppose I have a permanent magnet (axially magnetized) placed on top of the iron core of an electromagnet. I want to switch on the elctromagnet to repel the ...
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1answer
53 views

Could a man float in a large enough magnetic field to simulate zero gravity?

I know the magnetic field would need to be very large, but if an organisation like NASA with huge funding and resources could build a large enough device, could a man float in that magnetic field to ...
5
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1answer
22 views

Reason for poor signal strength of cellular phones inside a steel frame building

I could not clearly interpret the answer of the following question. So, hereby I wish someone could just make it easy to understand. And my question is: What makes the poor signal strength of cellular ...
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1answer
492 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
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0answers
24 views

superposition of two magnets

If I have two magnetic particles at x and y axis with strengths* $\mu_{x}$ and $\mu_{y}$; and another magnetic particle in x-y plane with strength $\mu=\vec{\mu}_{x} + \vec{\mu}_{y}$,then will the ...
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1answer
397 views

Force between two solenoids

How does one calculate the magnetic force between two coaxial solenoids, placed in a way their currents are in the same sense? There is a simple way to treat both as dipoles and then calculate the ...
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2answers
59 views

What does an oscillating magnetic field produce? [closed]

An alternating current produces a magnetic field. A oscillating charge produces light, which is an oscillating electric, and magnetic field mutually perpendicular to each other, and their motion is ...
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9answers
15k views
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1answer
88 views

Is the electric force a vector or a vector field?

The electric force (Coulomb's law) on a point charge $Q_2$ due to $Q_2$: \begin{gather*} \mathbf{F}_{12}=\frac{Q_1Q_2}{4\pi\epsilon_0}\frac{\mathbf{r}_2-\mathbf{r}_1}{|\mathbf{r}_2-\mathbf{r}_1|^3} \...
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1answer
37 views

Photon as a gauge boson for static fields

Excuse me if my question is naive, but I have never taken a proper QFT. I used to think of a photon as a quantum of EM field, quantum of light. But form QFT and particle physics prospective, photon ...
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3answers
43 views

Is the South Pole of an electromagnet always at the end where current is drawn into it?

I'm trying to determine in which direction a magnetic field will be produced in regards to the direction of current in an electromagnet. Will the end of the electromagnet from which current is drawn ...
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1answer
240 views

Why is an electric and magnetic field present in all universe? [closed]

Planet Earth has its fields due to the motion of molten metals in the core but how does this whole universe has its fields without any discontinuity? And, can we say for sure that fields are present ...
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1answer
28 views

Why does the magnetic field of the induced current oppose the change in the external magnetic field? [closed]

Why does the magnetic field of the induced current oppose the change in the external magnetic field? please help me to solve this Link:http://d2vlcm61l7u1fs.cloudfront.net/media%2F4dc%2F4dc03c3b-...
5
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0answers
58 views

Validity of gauge fixing in classical electrodynamics [duplicate]

I am working through Griffith, and was confused by some of the restrictions he imposed on the potentials in introducing the Coulomb and Lorenz gauge. It is easy to see that adding some arbitrary ...
6
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1answer
356 views

Could the Faraday's rotating wire experiment be explained without using Lorentz force?

I read Faraday's rotating wire experiment which resulted in the invention of the homopolar motor. He was clever enough to think it that way and make the wire rotate around one of the poles of the ...
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4answers
304 views

How do electromagnetic waves carry energy?

Its said that electromagnetic waves carry energy. Is this because these waves are made up of electric and magnetic fields which can cause changes to the stuff that falls with in their range? Is that ...
9
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1answer
156 views

Optical chirality and its possible hierarchy of generalizations

Optical chirality refers to a constant of motion of the electromagnetic field, which measures in some sense how chiral a light field is. Specifically, the pseudoscalar quantity $$ C=\frac{\...
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1answer
141 views

Can a magnetic or electric field deflect subatomic particles?

I always wondered if the subatomic particles can be deflected by a magnetic or electric field. Basically I am asking the viability of the typical "Force Field" in movies.
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0answers
149 views

What exactly is NASA's proposed mechanism for “propellantless” “EM Drive” propulsion? [duplicate]

Of course, this question runs perilously close to this site's prohibition against discussing non-mainstream physics. However, the accepted answer in meta about what is acceptable and what is not ...
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2answers
146 views

Does the ring (in the picture) experience Lorentz force?

Does the ring in the picture below experience Lorentz force? Or should I say it's just some magnetic force? (Notice that the poles repel eachother.) I am unsure because of the setting with the ...
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1answer
473 views

Is there any potential associated with magnetism

Can anybody please tell me if magnetism is a conservative force or if there is a field associated with it? How to reason? One thing I know is that the work done by a magnetic force is equal to $0$.
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0answers
29 views

How is there not an infinite regress in the emf of a motor?

Say we have a coil connected to a battery in a uniform magnetic field, perpendicular to the magnetic moment of the coil. This is a simple motor. There is a torque on the coil that varies with the ...
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1answer
45 views

How much and what kind of sunlight passes through a cloud?

I've read that 80% of sunlight is passing through clouds. Now there a small clouds and big clouds so it should be some average. Is this true or is the amount of sunlight passing throug a cloud really ...
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1answer
108 views

Amplitude of eliptically polarised light

In elliptically polarized light, can one define something called amplitude of Electric field? If yes, how do we determine it?
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2answers
106 views

HOW is an electric field induced when there is a time varying magnetic field?

I have just learnt electromagnetic induction. When the magnetic flux through a closed loop changes with time, a current is produced in the loop. My teacher told me that this was due to an "induced ...
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1answer
66 views

Clarifications on Ampere's Law [closed]

I have just learnt Ampere's Law, useful for calculating the magnetic field in situations having a high degree of symmetry. However, I have some conceptual doubts regarding it: Before I begin, I would ...
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3answers
66 views

Why conductors don't scatter light?

Air molecules can be oscillated by E field and re-radiate EM waves in different directions. However, if light is shined to a conductor the E field oscillate the free charges but the effect is to ...
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2answers
244 views

Can you create a powerful magnetic field out of confined circulating electrons only?

Would it be possible, regardless of how efficient it was to do something like this, or why you would actually do it, to generate a really powerful magnetic field simply by producing a cycling electric ...
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1answer
435 views

Voltage across an inductor contradicts Lenz's law?

Imagine a simple circuit consisting of an alternating current source connected to an inductor. Assume they are connected in the following fashion: AC source - terminal A - Inductor - terminal B - AC ...
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5answers
5k views

How did physicists know that there are two kind of charges?

Problems The question I am about to make is either too stupid or hasn't bothered anyone because its obvious because I can't really find the answer anywhere. I am currently studying electricity and ...
3
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1answer
162 views

Is Biot-Savart Law valid for time-varying currents unlike Ampere's law?

I have just finished learning the basics of magnetism, and it should be noted that I am not very familiar with Maxwell's equations. Note: In the question, when I say "Ampere's Law", I am referring ...
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1answer
49 views

Find the electric field of a uniformly polarized sphere

The problem statement, all variables and given/known data We want to calculate the field of a uniformly polarized sphere of radius=R Relevant equations $$V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \...
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2answers
264 views

Motor Speed depends on voltage or number of turns

What limit the size of motor speed? Does the speed of motor depend on the voltage applied or magnetic field strenght or frequency or what?
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0answers
11 views

Determining pole strength experimentally

Could anyone give me a quick explanation of what magnetic pole strength is or a website that does so? Also, how can i determine this value experimentally? Thanks in advance
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3answers
570 views

Helical motion of charged particle in external magnetic field

When an electron moves in uniform external magnetic field, with velocity not perpendicular, I understand that the magnitude of force is only due to the perpendicular component of velocity and is ...
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2answers
49 views

Gauss Theorem and Faraday's Law

I'm studying magnetic fields and I have a big problem. The Gauss theorem stats that the magnetic flux through a closed surface is null, since the line of flux enter and exit from it in the same amount....
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0answers
25 views

Bowl Shaped magnetic fields responsible to keep galaxies together?

David LaPoint released some videos on youtube. In part 2 he claims that because galaxies look similar to the shape of plasma created in his experiment they must be shaped also by external magnetic ...
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2answers
354 views

Domains of electromagnets

I know that magnetism is due to the alignment of domains of a magnetic substance. Due to this reason, an iron bar may be magnetized by stroking it with a permanent magnet such that its domains are ...
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2answers
47 views

Find the current enclosed in the loop

Magnetic field at point $(x,y,z)$ is given by $\overrightarrow B = \dfrac{B_0y}{\sqrt{ x^2+y^2}}\hat i - \dfrac{B_0x}{\sqrt{ x^2+y^2}}\hat j $. Find current enclosed in the loop $x^2+y^2=r^2$. My ...
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9answers
658 views

How do electrons know when a circuit is closed?

I was told that electrons do not begin flowing unless the circuit is closed. The electrons from the battery are not in the ends of wire when it is open, apparently, as there is no reason for them to ...
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1answer
66 views

is the sun going to make an electromagnetic pulse in the next 50 years?

EMP is very damaging and can cause blackouts and other bad results specially on electronic devices , so i heard that our sun is going to make an electromagnetic pulse during the next 50 years ..is ...
7
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1answer
68 views

How can a radiocontrolled watch receive waves of a couple of km long without a (large) antenna?

Some watches has the ability to make contact with DCF77. The DCF77 is a German longwave time signal and standard-frequency radio station. The highly accurate 77.5 kHz (approximately 3871 metres ...
2
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1answer
117 views

Maxwell's equations in covariant form

Maxwell's equations of electrodynamics in vector calculus form are \begin{align} \nabla \times \mathbf{B} - \partial_t \mathbf{E} & = \mathbf{J} \\ \nabla \cdot \mathbf{E} & = \rho \\ \nabla ...
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2answers
114 views

Why doesn't current induced by changes in flux affect the flux, while current induced by a battery does?

Faraday's law states $V=-\frac{\mathrm{d}F}{\mathrm{d}t}$, where $F$ is flux. Since $V=IR$ for passive circuits, $I = V/R = -\frac{1}{R}\frac{\mathrm{d}F}{\mathrm{d}t}.$ But by the Biot-Savart law, ...
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2answers
24 views

How to compute work needed to build a configuration of charges

Suppose an alignment of four charges in the vertices of a square. The first pair on one diagonal has positive charge and the other negative charge, all charges are of the same absolute value. length ...
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1answer
24 views

Eddy currents induced throughout the volume of the material or only the surface?

If a conductive slab has induced Eddy currents to oppose the change in magnetic flux, is the induced current uniformly distributed throughout the slab's volume or only at the surface? I might have ...
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1answer
245 views

How is Magnetic force on a current carrying conductor $Blb$

I was reading an answer about torque acting on a rectangular current carrying loop kept in a uniform magnitude field B. Force acting on each sides is $F_1$, $F_2$, $F_3$, $F_4$. It's written here : ...
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1answer
154 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, ...