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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125 views

Flux increase due to velocity?

I have a book question I'm trying to understand: The first bit is easy enough. The second part I was confused so I checked the solution: B is into the page. The flux increases as the bar moves ...
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1answer
55 views

Calculating back-reaction forces for an ensemble of slowly moving, classical charges

Suppose you have a set of charges that are Newtonian (not quantum and not fast-moving) point particles. They are subject to known (but not necessarily constant) external forces ($F_{ext}$), as well as ...
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0answers
67 views

Hertzian dipole in time varying electric field

Suppose we place a Hertzian dipole (short, ends loaded with capacitance) in a time varying electric field $\vec{E}\left(t\right)$, with magniture $E\left(t\right)$ and direction as shown in this ...
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0answers
51 views

Demagnetization of a permanent magnet and lenz's law

This video ( http://www.youtube.com/watch?v=Vs3afgStVy4 ) demonstrates lenz's law, if the current produced by the magnet fall induces an opposing magnetic field , after many tries , can this field ...
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0answers
55 views

Long range repulsion in anomalous solids

As far as I know things like rocks, walls, rubber balls, polished tables etc. exert a short range repulsive force on other everyday objects that is responsible for hardness, softness, collisions, ...
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3answers
187 views

Hard disk rotational frequency

I noticed the other day that the rotational frequency of typical consumer grade HDD are either 5400rpm or 7200rpm. These correspond to 90Hz and 120Hz respectively. Given that in parts of the world ...
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1answer
132 views

General Physics II Practice Question [closed]

I have a test in a few hours, and my professor gave us a practice test, and I'm stuck. Could you give me a hint as to how to approach this problem, equations I could use. It's an algebra based class ...
11
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4answers
3k views

How long does a permanent magnet remain a magnet?

I have a bunch of magnets (one of those game-board thingies) given to me when I was a school-going lad over 20 years ago, and the magnets feel just as strong as it was the day it was given. As a ...
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4answers
1k views

Gravity stronger than electromagnetic force in a black hole?

Well, the question has somewhat been answered before, but there's one part missing, which - I'd think - is in conflict with the physical laws. The earlier reply says that the gravitational pull even ...
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2answers
102 views

Is mass of a particle changed when it is charged? [closed]

If a particle of mass $M$ is given an electric charge $Q$, will its mass change?
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2answers
3k views

Does special relativity make magnetic fields irrelevant?

I've heard that special relativity makes the concept of magnetic fields irrelevant, replacing them with relativistic effects between charges moving in different velocity frames. Is this true? If so, ...
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1answer
356 views

Are dc and ac currents produce electric field? [closed]

I have four different situation and i want to learn what kind of field (electric or magnetic) each produces and which produces electomagnetic waves? 1)dc current flow in a conductor 2)ac current ...
4
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2answers
785 views

Can extra-solar gamma rays reach the Earth's surface?

Can gamma rays of high enough energy entering our planet's atmosphere reach the surface (50% probability)? Or, in other words, is there a window for extremely high-energy gamma rays like for the ...
4
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1answer
293 views

What is the magnitude of the force on a charged particle due to electromagnetic radiation?

Suppose there is an electromagnetic wave moving forward in the $\mathbf{\hat{k}}$ direction. Its electric/magnetic field components are given by: $$\mathbf{E} = E_0 \sin(kz - \omega t) ...
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1answer
43 views

vector product between $ds$ and other portion of current loop

In the answer section it is written that,The magnetic field at O due to the current in the straight segments $AA^\prime$ and $CC^\prime$ is zero because ds is parallel to along these paths. My ...
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2answers
262 views

Resistance of aluminium rectangular wire

I am working on upgrading an electromagnet design program. There are currently two types of wire used for the coil, circular and strip (read as: rectangular). The current algorithms in this program ...
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4answers
214 views

What is the magnetic effect on either of the charges moving parallel

Consider two electrons moving parallel to each other in the same direction with same constant velocity. Will they experience any force due to either of them?
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7answers
4k views

What is the electric field generated by a spinning magnet?

Consider a cylinder of permanently magnetized material, with uniform magnetization pointing along the cylindrical symmetry axis (the $z$-direction). The magnet is rotating about its cylindrical ...
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1answer
145 views

Lenz law and magnetic pole

When a magnetic north(N) pole is placed close to an coil with out energy source, the coil behaves like an magnet and we find a North pole which opposes the magnet bar which was approximating onto the ...
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5answers
1k views

Is the EmDrive, or “Relativity Drive” possible?

In 2006, New Scientist magazine published an article titled Relativity drive: The end of wings and wheels1 [1] about the EmDrive [Wikipedia] which stirred up a fair degree of controversy and some ...
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1answer
160 views

Will a moving neutron produce a magnetic field around it?

Will a moving neutron produce a magnetic field around it? I know that neutrons have no charge, so magnetic field should not be produced along it...but neutrons have a magnetic moment. So why can't ...
2
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2answers
791 views

What is the force between two magnetic dipoles?

If I have two current loops parallel to each other with currents I1 and I2 and radii R1 and R2 a distance z from each other, what is the force between them? What would change if they were two ...
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1answer
111 views

Electric field and capacitance across a resistor

Using a simple lattice model of conduction, where electrons are accelerated by an electric field, and are slowed down by bumping into the lattice, you get the following equation for current density: ...
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1answer
122 views

Particle Spacing in a Vacuum

Four questions: (To start off, I know very little about physics it isn't even funny (I probably use a ton of wrong terms here and leave out vital information, if so I will try to edit it in as you ...
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2answers
86 views

Time difference in transmission of AC and DC

Is there any time difference while considering the transmission of AC and DC ? Is either one of them faster than the other one in terms of transmission of energy/power from one point to another? I ...
2
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0answers
60 views

Gravity and Larmor effect

I have a Q: Does "Equivalent Principle" and "Larmor effect" imply that the charged particle should radiate electromagnetic wave if it is at rest in uniform gravitational field (like it is at rest on ...
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1answer
145 views

Is there any metal having the properties of rubber? [closed]

I have seen tires of vehicles to be made of rubber with air filled tube inside.Why can't we have whole tire to be made of rubber? I hope there would be some use of the air filled tube.Then What is ...
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1answer
87 views

Accelerated charge inside sphere (again!)

Sorry to go on about this scenario again but I think something is going on here. Imagine a stationary charge $q$, with mass $m$, at the center of a stationary hollow spherical dielectric shell with ...
8
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2answers
387 views

current in wire + special relativity = magnetism

Current in wire + moving charge next to wire creates magnetic force in the stationary reference frame OR electric force in the moving reference frame from special relativity due to change in charge ...
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0answers
115 views

Non-zero charge density due to Lorentz contraction in current carrying wires

In trying to answer this question I came across the following problem. The original question relates to the idea that what looks like a magnetic field in one reference frame, ends up as an ...
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1answer
954 views

Potential energy of the dipole-dipole interaction for two parallel dipole moments

I am looking for an equation that gives me the potential energy of the interaction between two parallel dipoles.
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1answer
616 views

How does a Tesla Coil exactly work? [closed]

How does a Tesla Coil exactly work? I am currently making a Tesla Coil in school but before I start, I want to know exactly how does a Tesla Coil work? I understand the various electrical components ...
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0answers
49 views

Does pure electric dipole have higher order moments?

Of course for the standard configuration(i.e. two opposite charges separated by some distance), there exist higher order multipole moments. However for an ideal dipole(those dipoles associated with ...
2
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1answer
122 views

is it possible to have magnetic flux density B not in the same direction of magnetic field intensity H?

it is said that direction of magnetic flux density B in the same direction of magnetic field intensity H for isotropic media so what is isotropic media and is it possible to have B not in the same ...
14
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3answers
1k views

Is one way glass possible?

I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?
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0answers
83 views

magnetic fields and symmetry

When we compute the magnetic field for some configuration (with enough symmetry), we usually use the fact that the magnetic field is orthogonal to any plan of symmetry for the distribution of current ...
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1answer
196 views

How to imagine the first few moments of an LR circuit?

For example, there's a very simple circuit which only contains on resistor. So according to Ohm's law, we have: $\mathrm{emf} = IR$ As we know when time $t = 0$, the current must be $I = 0$. However, ...
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1answer
85 views

Determining the location of magnetic moments

The magnetic moment of a closed current loop is $$\mathbf{m} = \frac{I}{2}\int\mathbf{r}\times d\mathbf{r}.$$ Note that $\mathbf{m}$ is independent of any coordinate frame. How, then, does one ...
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2answers
125 views

Can protons in the nucleus of an atom be aligned by electromagnetic fields?

Can protons in the nucleus of an atom be aligned by electromagnetic fields? If so can it be done around $-135°C$ zero?
1
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1answer
62 views

Uniqueness of equilibria in electrostatics

I have the following problem. Suppose we place some continuous charge distribution (with total charge $Q$)on some conducting domain. The charge will redistribute itself on the domain until it's in ...
2
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0answers
83 views

Quadrupole potential generation in Paul trap

I am currently getting familiar with the concept of the Paul trap and the underlying physicle principles. I do understand what kind of potentials are needed to trap charged particles, e.g. for the 3D ...
3
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2answers
171 views

What is the theoretical justification for a fluid flow's being irrotational?

I am not a fluid dynamicist, and I really just began thinking about this problem as my curiousity drew me into building an answer for the question What really allows airplanes to fly?. It is very ...
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0answers
753 views

How to calculate magnetic pole strength?

I have 2 magnets. I need to know the force between them. In a previous Phys.SE question, conclusion was: we need to use a dipole-dipole interaction equation, which included m, which the magnetic ...
2
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1answer
84 views

Question about complex emissivity and complex permeability

Consider a linear, isotropic material. We can then write: $$\textbf{D}(\textbf{r},\omega) = \epsilon(\textbf{r},\omega)\textbf{E}(\textbf{r},\omega)$$ In phasor notation. The complex emissivity ...
2
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1answer
119 views

If Electricity and magnetism are the same viewed from a different reference frame then is electricity medium dependant?

If Electricity and magnetism are the same viewed from a different reference frame (they are the same force as unified by maxwell) then is electricity medium dependant? I came to this question when ...
2
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1answer
1k views

Force between two bar magnets

I need to know how to calculate force between two bar magnets. I searched and found an answer on Wikipedia, but I don't really trust Wikipedia, a lot of crazy stuff is posted there. So I searched ...
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0answers
39 views

Anisotropy and demagnetizing field

I'm trying to calculate the anisotropy constant of a ferromagnetic material. Then, of course, I need to worry about the demagnetizing field. However, a book I'm reading claims that we can calculate ...
2
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1answer
205 views

Why are lab Magnets painted red?

Wy are lab magnets painted red in color? I tried searching everywhere but couldn't get a satisfactory answer.
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0answers
25 views

Magnetic field distrotion

Does one exist, or do you think it would be possible to design a tracking magnetic field distortion detector to detect fast moving magnetic anomalies in our air space. ie; track a stealth aircraft or ...
7
votes
2answers
194 views

Time dilation only on electromagnetic force?

We've seen by experiment that the speed of light c appears to be constant for each observer (leading to all well-known consequences of relativity). I'm wondering if this appearance of constancy of c ...