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.

learn more… | top users | synonyms (6)

2
votes
2answers
22 views

How electromagnetic waves carry energy?

Its said that electromagnetic waves carry energy. Is this because these waves are made up of electric and magnetic field which can cause changes to the stuff that falls with in their range ? That is ...
1
vote
0answers
11 views

Why the motion of rotating magnet doesn't stop if we use a superconducting wire?

I would like to know why magnets rotated,wouldn't stop their motion if we place a superconducting wire as said by William Beaty at MadSci Network.
0
votes
2answers
279 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 ...
0
votes
2answers
23 views

Can bending spacetime produce electromagnetic fields?

Let's say that we can somehow bent spacetime, can this produce electromagnetic fields? or EMF can only be emitted from charged particles of matter?
1
vote
1answer
151 views

Spherical magnet inside a solenoid

When passing a bar magnet through a long solenoid why is it that the induced emf when the magnet is in the middle of the solenoid is zero? And if a spherical magnet is put inside the solenoid, will ...
0
votes
2answers
52 views

Electromagnetic Radiation and Communication!

I read that the accelerated charges create electromagnetic field/spectrum which consists of following different waves: gamma, X-rays, ultraviolet, visible light, infrared, microwaves, & radio ...
0
votes
2answers
3k views

Potential energy from opposing magnets repelling each other with a gap of 1 mm

I have two powerful rare earth magnets, that are separated by a distance of 1 mm. I applied energy to bring them closer to each other, hence increasing the potential energy. Now, when one of the ...
0
votes
1answer
387 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 ...
0
votes
2answers
37 views

Polarized light from any suface?

From a textbook I read something like this: "When sunlight is reflected from a horizontal surface, the plane of incidence is vertical, and the reflected light contains a preponderance of light that is ...
1
vote
2answers
711 views

Can we increase the magnetic flux for a permanent magnet?

When we pass current to the permanent magnet does its magnetic flux, magnetic property of attraction and repulsion increases? if possible Is there any other way for increasing the magnetic flux?
0
votes
1answer
477 views

Coercivity of a ferromagnetic material?

I understand that coercivity is the field/force required to demagnetize/magnetize a ferromagnetic material. What if we had two opposite magnetic fields of different strengths values H acting on the ...
1
vote
0answers
22 views

Geometric Algebra formulation of EM in nonuniform dielectric media

Normally, there is a straightforward formulation of Maxwell's equations in free space under the GA framework, which reduces to (picking the right units): $$ \nabla F = \mu_0 J $$ with some ...
0
votes
3answers
924 views

Understanding magnetic force on charged particle

if we put any charged motionless or static particle in the constant magnetic field, then why does it don't feel a magnetic force? Mechanism by which electric and magnetic fields interrelate I have ...
1
vote
0answers
39 views

Can a lightning strike cause your car to not run? [migrated]

If lightning strikes a tree in your yard and your car is close by, can this cause your car to not work properly? I had an employee call in stating that lightning struck a tree beside their mobile ...
1
vote
2answers
144 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?
1
vote
1answer
53 views

Could I pick up a human with a strong enough magnet? [duplicate]

Could I pick up a human with a strong enough magnet? Humans contain magnetic materials, such as iron.
13
votes
6answers
9k views

What is canonical momentum?

What does the canonical momentum $\textbf{p}=m\textbf{v}+e\textbf{A}$ mean? Is it just momentum accounting for electromagnetic effects?
-3
votes
0answers
19 views

Eigen energy for charged particle in a magnetic field [on hold]

How can I determine the eigen energy for charged particle in a magnetic field?
3
votes
1answer
2k views

How much magnetic field will be required to levitate a human? [duplicate]

According to this video: http://www.youtube.com/watch?v=BqKeiiezqzc it should be possible to levitate humans because the water in our bodies is diamagnetic - but it is stated (at 1:14) "although ...
9
votes
2answers
730 views

Do stars remain electrically neutral? [duplicate]

How electrically neutral do stars remain through their lifetime? As an example, I could imagine processes such as coronal mass ejections leaving the Sun in a slightly charged state. Are there such ...
-1
votes
0answers
31 views

How do I get the maximum EMF in this problem? [on hold]

Concern is often expressed regarding the potential adverse effects of oscillating electric and magnetic fields on the human body. Consider a typical magnetic field created by mechanical ...
0
votes
0answers
9 views

Electromagnetism question involving magnets on the ends of a metal pole

My teacher showed us a phenomenon in school involving a metal pole with two magnets on each end. The magnets are aligned so that both south poles are stuck to each end of the metal pole. This results ...
2
votes
3answers
53 views

Deriving the field equations of a given action

Provided an action: $$S[A_\nu] = \int\left(\frac{1}{4}(A_{\gamma,\mu}-A_{\mu,\gamma})(A_{\zeta,\alpha}-A_{\alpha,\zeta})\eta^{\gamma\zeta}\eta^{\mu\alpha}+\frac{1}{2}\nu^2A_\mu A_\gamma -\beta A_\mu ...
0
votes
0answers
16 views

How Do I find the Thermal increase of a ideal gas flowing through a magnetic field? [on hold]

I am thinking of turning dissociated 2H_2 and O_2 into plasma by forcing it through a electromagnet field. what are the equations to determine the thermal energy added to the gas. I'm thinking to ...
1
vote
1answer
399 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 ...
0
votes
1answer
55 views

Motion of an electron in a magnetic and electric field [on hold]

I have this problem where i should find the direction and magnitude of the electric and the magnetic force on the electron. E = 1000 N/C B = 2,5 T v = 500 m/s ...
0
votes
0answers
25 views

Expressing charge density in terms of spherical multipoles

How to express the charge density in terms of the full set of the spherical multipole moments? That is, how to invert the relationship $$ Q_{lm}=\frac{4\pi}{2l+1}\int ...
3
votes
2answers
186 views

How can Maxwell theory be viewed in terms of two-layer structure?

I'm trying to learn more about Maxwell equations and stumbled upon an essay by professor Freeman J. Dyson from Princeton. He explained Maxwell theory in a very interesting way. The modem view of ...
1
vote
0answers
34 views

Lab experiment: hysteresis disappears, reappears and then disappears again. How?

In my college laboratory we were assigned an experiment to measure the hysteresis curves of a certain ferromagnetic material at different temperatures. Sounds simple, right? Well, the block of Monel ...
-1
votes
0answers
15 views

PSD image detection

A laser is pointed on a surface, such that it is reflected onto a PSD (position sensing photodiode). Before light reaches the PSD, it goes through a plano-convex lens to get focused. Now, if the ...
0
votes
1answer
60 views

How do you find the electric field corresponding to the magnetic field? [on hold]

If we are given the magnetic field $B$ how can I find the corresponding electric field? The example brought up at the end of my lecture was $B = B_o \cos(ky-\omega t)$ in the $k$-direction. I am ...
2
votes
1answer
40 views

EM: relative permittivity

After having defined the relative permittivity in lectures, I have problem understanding why it is a complex quantity. Thank you for your help,
0
votes
1answer
38 views

What does it mean physically to set $\exp(ikr)=1$ in the dipole approximation?

In the dipole approximation one sets the $exp(ikr)=1+ik.r+...=1$. ($|<f|exp(ikr)\epsilon.r|i>|^2$). Which makes $k.r=0$. What does it mean physically? Is the plane transverse wave converted to ...
0
votes
1answer
229 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 : ...
1
vote
2answers
71 views

Definition of the Lorentz transformations [on hold]

Until very recently I believed that the Lorentz transformations were defined as "the transformations that carry one inertial reference frame into another". In Wikipedia's page we find something along ...
4
votes
5answers
335 views
+200

Can you deduce absolute motion through magnetism?

Trying to understand magnetism I stumble into this example: Suppose there are two electrons travelling side by side in deep space (say, between Mars and Jupiter) at 1 cm distance at .99 c. In this ...
1
vote
1answer
190 views

Is it possible to pass electric current through magnet without affecting it?

Suppose we have a row of $5$ electromagnets, with a copper wire connecting them. Is it possible to create magnetic field in the $4^{th}$ magnet without affecting the $1^{st}$,$2^{nd}$,$3^{rd}$ and ...
-4
votes
1answer
45 views
1
vote
2answers
601 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 ...
0
votes
1answer
132 views

What is the strength of the magnetic field required to penetrate an average human body?

Introduction Suppose you are an experimental nanobot researcher trial-ling a new form of medication that involves activation and control of nanobots within the cells of the interior of the human body ...
0
votes
1answer
21 views

Approximating magnetic field at center of current loop by solenoid of 1 turn

It's well known that by application of biot-savart law, the magnetic field at the center of a loop of current is $\frac{\mu_0 I}{2r}$. Now when we consider a solenoid, isn't the resulting magnetic ...
1
vote
3answers
4k views

How is bound charge and free charge possible?

I am studying Introduction to Electrodynamics by Griffiths and I came along a concept I cannot seem to understand properly. The concept of free charge AND bound charge. I do not understand how we can ...
1
vote
1answer
19 views

How to find the force of a magnetic field, resolving the components?

So, in answering this question the book resolves the components of the Force vector in this manner; $\mathrm dF_x= \mathrm dF \sin \theta$ $\mathrm dF_y= \mathrm dF \cos \theta$. And then, ...
0
votes
1answer
36 views

How do you calculate the expected force of an electromagnet?

What is the equation to find the expected force of electromagnet? What do the variables mean and how do you find each variable?
0
votes
2answers
333 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 ...
1
vote
1answer
171 views

Cylindrical capacitor in an electric circuit

I've come across a tricky question and would appreciate some hints or explanations as to why the given solution is the way it is. The question reads as follows: A coaxial cable consists of a wire ...
5
votes
1answer
330 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
votes
1answer
30 views

The MRI signal: why do we consider the phase in the MRI signal

I am trying to understand the imaging principles behind MRI and I was looking at some lecture slides found here Specifically, I am looking at slide 41 where we look at some of the equations regarding ...
0
votes
0answers
29 views

Lorentz sphere correction

I am studying Lorentz surface correction for magnetic fields. I know that if we consider a uniform distribution of magnetization, the field can be computed as three contribution: $H+H'+H''$ where $H$ ...
20
votes
5answers
3k views

How can there be net linear momentum in a static electromagnetic field (not propagating)?

I understand from basic conservation of energy and momentum considerations, it is clear in classical electrodynamics that the fields should be able to have energy and momentum. This leads to the usual ...