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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1answer
52 views

How does radiation degrade mechanical parts and electronic devices?

I'm running out of places to look (lots of Googling, SE, [articles and books are too specific and never give a good overview]), and yet I am still unsure about how exactly radiation can degrade ...
8
votes
1answer
3k views

Can microwaves affect WiFi?

I listen to the radio via my iPad with wifi. When I switch the microwave oven on, the radio cuts out. When the microwave oven is finished, the radio comes back on. (This is 100% reproducible!) So - ...
0
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0answers
15 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 ...
2
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3answers
214 views

About field gradient

I read the term field gradient in most of the article about magnetic field. I search it online but most of the explanation is about the math. I wonder in physics, what the gradient field really mean? ...
-1
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0answers
22 views

Is it possible to focus an electromagnetic field such as an aura into a stream of pure energy? [closed]

Is it possible to focus an electromagnetic field such as an aura into a stream of pure energy? http://www.biofieldglobal.org/what-is-human-aura.html
0
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2answers
59 views

Proof that work is the same whaever the path of approach for two charges

I have a quick question on a figure that outlines a proof. There is a stationary charge $q_1$ and is kept fixed. $q_2$ is moved to the same position along two different paths at a fixed distance ...
1
vote
1answer
287 views

Force on a coil inside of a voice coil

as a homework exercise we were given the following question: Given the following voice coil: With depth = 20 mm Permanent magnets with B = 1.23 T, Ur = 1.1 The coils has 20 turns, I = 1 Ampere. a) ...
3
votes
2answers
59 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 ...
3
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2answers
178 views

Looking for lists of student difficulties with electromagnetism, circuits (DC and AC)

I'm trying to help with an Instructor's Guide for an introductory calc-based physics text, and it would really help if I could locate some lists of typical student difficulties with topics like ... ...
1
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1answer
348 views

How is the current flow perpendicular to the wire?

This answer gives a great explanation of how surface charge builds up to force the current to move perpendicular to the wire: http://physics.stackexchange.com/a/102936/41086 However, it fails to ...
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3answers
135 views

Are magnetism and electricity the same thing? [closed]

I have read at certain place electricity and magnetism are the same thing, bit in reality we see both have different properties.
2
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3answers
53 views

Does the equation CV = q break down when V is small or a wire is very long?

I'm trying to understand how the equation $CV=q$ relating the voltage difference and charge stored on a charged capacitor breaks down under extreme circumstances. In most problem statements that I'm ...
3
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3answers
364 views

How do electrons actually move in a circuit?

Last year, we were taught about electricity, about how electrons move in a closed circuit. But as our teacher had not taught us about electric fields yet, she gave us a simplified model of motion of ...
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2answers
961 views

Meaning of boundary condition for steady current density?

Although I understand the derivation of boundary condition in case of steady electric current but I did not understand, that the electric field which is in direction of $J$ current density that is ...
-1
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0answers
23 views

Magnetic moment of a paramagnetic crystal

I've been having some trouble with a paramagnetism problem from my Statistical Mechanics class textbook (F. Mandl, Statistical Physics, 2nd edition, p. 25). The problem is as follows Since the ...
3
votes
1answer
114 views

How can Drift Velocity of an electron causes change?

Assume we have a conductor that has current flowing and its placed in a magnetic field so that it experiences the Lorentz force, and it gains Kinetic energy due to that force. Would drift velocity ...
1
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1answer
87 views

Real life physics problem: Why is my desktop computer affected by my plasma ball?

Note: this is strictly a physics question, not meant to be an advertisement I was running my desktop with a plasma ball on the side. The desktop has a touch screen enabled. I started to notice that ...
2
votes
3answers
1k views

Why the electric potential of earth is zero?

For a localized charge distribution the potential is set to zero far away from the charge distribution (at infinity) Now, when grounding a conductor, i.e. connecting it to Earth, it is said that we ...
1
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1answer
22 views

where does the term half in the formula of electrostatic potential energy comes from?(system of point charges)

Electrostatic potential energy stored in a system of point charges (from wikipedia) The electrostatic potential energy $U_E$ stored in a system of N charges q1, q2, ..., qN at positions r1, r2, ...
3
votes
1answer
170 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 ...
0
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2answers
190 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 ...
3
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0answers
51 views

What is the origin of the “polarization catastophe”?

According to the Clausius-Mossotti relation, $$ \frac{\epsilon_r - 1}{\epsilon_r + 2}=\frac{n\alpha}{3\epsilon_0} $$ So when $n\alpha = 3\epsilon_0$, the relative permittivity $\epsilon_r$ ...
9
votes
7answers
19k views

Can magnetic fields be redirected and focused at one point?

I know that magnetic fields can be redirected, but... given a situation where you have static magnetic field over a large area, and you want to quickly change the magnetic field strength. Is it ...
1
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1answer
117 views

Free Electromagnetic field in Lorenz gauge

To get rid of the extra term in the QED Lagrangian we need to redefine the electromagnetic four-vector: $A^{\mu} \rightarrow A^{\mu} - \frac{1}{c} \partial_{\mu} a(x)$ where $a(x)$ is the function ...
0
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0answers
35 views

Maxwell Equation in dispersive media Griffiths

I am wondering where is the following equation (9.162) of Griffiths Electrodynamics 4e from? $$ \nabla^2\tilde{E} = \tilde{\epsilon}\mu_0{\partial^2\tilde{E}\over\partial t} \tag{9.162}$$ I know ...
4
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1answer
236 views

Boundary conditions on current carrying wire

I'm trying to simulate by finite elements method Maxwell equations for a current carrying wire. My 3d geometry consists of a cylinder and a box containing it. I will use a mixed formulation and ...
0
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1answer
30 views

Why does the inductance of a coaxial cable not depend on the number $N$ of coils?

Suppose we have a long coaxial cable like in the following figure: I want to compute the self-inductance $L$ of the cable. As I understand, given a coil with $N$ closely winded turns, through which ...
2
votes
2answers
36 views

Is the photon truly not absorbed in Raman scattering?

In reading about Raman Scattering, I was thinking while reading it "okay, incident photo absorbed by molecule, molecule goes to higher energy vibrational state, molecule re-emits photon with either ...
0
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0answers
32 views

How does the “computer fan with magnets” generator “work”? [duplicate]

This question is in relation to the following YouTube video: https://www.youtube.com/watch?v=jiAhiu6UqXQ In it, an electrical generator is shown consisting of a CPU fan with thin magnets attached to ...
0
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1answer
39 views

How can equipotential planes differ in potential in an uniform field?

I'm trying to solve an exercise that asks me the field strength of an uniform electric field where equipotential planes differ by $1\ \mathrm{V}$ and are $2.5\ \mathrm{cm}$ apart. First of all, I ...
0
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1answer
75 views

Magnetic flux of a loop due to another loop

The scenario is the following, I am given 2 loops with the same radius, r, a distance of d, and same current of I. In the left loop the current goes counter clockwise, in the right loop the current is ...
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0answers
45 views

Does Lorentz force affect the magnetic field?

When a charged particle moves thru magnetic field, it is affected by Lorentz force. But does the magnetic field surrounding the particle experience a force opposite to the particles Lorentz force ? ...
0
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0answers
25 views

Magneto Optical Kerr Effects

I have a few questions on MOKE setup. Firstly, why is calibration of the coils necessary? Is it to get a relationship between the voltage and the Magnetic field? Secondly, why do we have to normalise ...
0
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0answers
18 views

Is polarization a meaningful notion for an EM mode in a close cavity?

For a generic close cavity, I suspect that all the modes are non-degenerate? Therefore, in each mode, at each point, the E field has a definite direction, and consequently, it is meaningless to say a ...
11
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8answers
4k views

Is it possible to separate the poles of a magnet?

It might seem common sense that when we split a magnet we get 2 magnets with their own N-S poles. But somehow, I find it hard to accept this fact.(Which I now know is stated by Gauss's Law) I have ...
0
votes
1answer
241 views

Magnetic fields in transformers and back emf?

i am having some trouble with understanding the magnetic fields inside transformers and how they relate to back emf. My first query is: is the magnetic field produced inside the soft iron core ...
1
vote
1answer
35 views

Is the electron's magnetic dipole moment influenced by the measurement method?

The electric charge of an electron at rest is a constant value and is not influenced by the measurement instrument. The measurement instrument by itself can give more or less accurate result, but does ...
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0answers
12 views

what is the difference between mictomagnetism and spin glass?

What is the difference between mictomagnetism and spin glasses? I mean what are the distinguishing characteristics of them which makes them separate?
0
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1answer
23 views

Induced current from moving coil through non-uniform magnetic field

A rectangular coil with dimensions $L_x$ and $W_y$ , mass $m$, $n$ turns , and resistance $R$ is moving at an initial velocity of $v_i$ when a non-uniform magnetic field pointing directly up ...
2
votes
1answer
96 views

What is the sum of the electrons' magnetic moments in a wire?

Electrons have magnetic dipole moment. This magnetic moment will be influenced in an electric field in case the electron get moved non-parallel to the current. The magnetic moments will be more or ...
2
votes
1answer
89 views

Problem with relativity of acceleration

In this answer http://physics.stackexchange.com/a/92833/36977 John said that acceleration is not relative in the general theory of relativity. But as we all know, accelerating charges emit ...
-1
votes
2answers
104 views

Magnet arcs assemly

Is it possible to join multiple Neodymium magnet arcs (shown blow), which are radially magnetized, to create a cylindrical ring unity that is also radially magnetized? If it is not possible, how to ...
0
votes
1answer
230 views

Calculating 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. ...
1
vote
1answer
63 views

Propagating higher order Hermite Gaussian modes. What are complex amplitude coefficients?

I've been tasked with writing a code (in MatLab, but I'm currently using Mathematica because I don't know MatLab %\ ...) to simulate the propagation of a Gaussian beam. I don't really know anything ...
0
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0answers
14 views

Can a material be diamagnetic to electromagnetic waves, such as the visible spectrum

Diamagnetism is shown to repel a magnetic field and therefore the material counterpart of that field. Can an object be diamagnetic to electromagnetic waves, and repel them? I understand that there is ...
1
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0answers
45 views

Electromagnetism and magnetic fields

Would it be possible to fill hollow non-magnetic blocks of metal with ferromagnetic fluids and use magnetic fields to move the blocks in a certain way? I am only asking this because I think that if it ...
1
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1answer
49 views

Two objects with mass m with charge q connected to spring [closed]

I am taking Physics 201 on Yale Open Courses. I having trouble with the 5th problem in the problem set 1, which says as follows: Two sphere of mass m and negligible size are connected to two ...
3
votes
3answers
221 views

Electromagnetism Boundary condition

The dielectric slab surrounded by air as shown in diagram has permittivity $\epsilon$ different from air and permeability almost same as air. Electric field everywhere within the slab is given to be ...
1
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1answer
52 views

Why can't I measure electric potential from source to point according to this formula

The formula for electric potential of points A and B in the presence of an electric field due to a point charge where $R_a$ and $R_b$ are the distances from source to point A and B respectively is: ...
2
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2answers
56 views

Relation between magnetic moment and angular momentum — classic theory

How do I prove the relation between the vectors of magnetic moment $\vec\mu$ and angular momentum $\vec L$, $$\vec\mu=\gamma\vec L$$ ? Many text books and lecture notes about the principles of ...