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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4
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1answer
226 views

How is relativistic N-body simulation possible without knowing the entire histories of each particle?

In n-body simulation you need to know the positions of the particles in order to calculate the force between them. The new velocity of each particle can then be calculated given a simulation timestep ...
2
votes
2answers
1k views

Comparing effect of electric and magnetic dipoles on their fields

So at the end of one of my prof's lectures he gives us something to think about: Both electric and magnetic dipoles tend to line up with their respective fields. Materials made out of ...
0
votes
3answers
679 views

Creating a 2d magnet simulator [closed]

I need to create a "simple" magnet simulator, unfortunetely I have little to no physics knowledge. The best way to describe my idea is, imagine a hockey table. There's a disk and I need to throw it ...
0
votes
3answers
7k views

What is the use of this formula 1 Tesla = 1 Newton/Ampere/Meter?

What does Newtons/Ampere/Meter stand for? From this formula: 1 Tesla = 1 Newtons/Ampere/meter what can it be used for? To do what? Ampere/meter Is the same unit as a field's intensity H? Or what is ...
0
votes
1answer
634 views

question about methods of images in magnetostatics

I did not understand if a current I above a conducting surface why we take image of current to find magnetic field intensity why not take the effect of actual current only . And is this method and ...
-4
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1answer
2k views

Tesla to Newtons [closed]

Is it possible to convert Tesla to Newtons of force? Or magnetization force H:(A/m) to newtons?
0
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1answer
179 views

Magnetic core, and a DC solenoid

A DC solenoid creates a magnetic field B. A highly permeability magnetic core is added to solenoid to increase B. Now, there is change in flux, due to the increase in magnetic field. What would be ...
3
votes
2answers
150 views

Is there a differential equation that can represent a circuit with an arbitrary voltage source connected acrorss an antenna?

An RLC circuit with a voltage source can be characterized by the differential equation: $$ LC\;\ddot{I}\left(t\right) + RC\; \dot{I}\left(t\right) + I\left(t\right)-C \;\dot{V}\left(t\right) = 0 $$ ...
0
votes
1answer
396 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 ...
2
votes
2answers
644 views

Neither Biot-savart nor Ampere Law can solve this problem?

I'm confused about the use of the Ampere's Law and the Biot-Savart Law due the inconvenience of each law. I want to calculate the magnetic field due to current carrying a circular loop over itself, ...
0
votes
3answers
712 views

AC through a pure inductor

I've studied the AC circuit for an ideal inductor in many physics books. After deriving the final equation for current the integration constant $C$ is assumed to be $0$ by giving inadequate reasons. ...
10
votes
4answers
4k views

Maxwell's Equations using Differential Forms

Maxwell's Equations written with usual vector calculus are $$\nabla \cdot E=\rho/\epsilon_0 \qquad \nabla \cdot B=0$$ $$\nabla\times E=-\dfrac{\partial B}{\partial t} \qquad\nabla\times ...
3
votes
2answers
269 views

The meaning of potential in Bohm-Aharonov experiment

The Bohm-Aharonov experiment involves a magnetic field inside a cylinder which is zero outside that cylinder. Nonetheless it affects the electrons moving outside the cylinder. The explanation for this ...
0
votes
1answer
218 views

Voltmeter Question [closed]

I understand that a voltmeter is used for measuring potential electrical difference, but how exactly should said voltmeter be connected with the resistor in circuit?
-3
votes
1answer
91 views

What exactly is resistance?

I am trying to teach myself about electricity and magnetism and I have a few questions about resistance. How does resistance of say a long wire compare to that of a a short wire? what about thick and ...
3
votes
3answers
479 views

Understanding the Ampere's Law

We want to study the magnetic field at point $P$. So, from the figure we take that: $\oint_{L_1} B\cdot dl=\mu_0 I_1$ $\oint_{L_2} B\cdot dl=\mu_0 I_2$ $\oint_{L_3} B\cdot dl=\mu_0 I_2$ The ...
1
vote
0answers
67 views

Transitions in a magnetic refrigeration

The graph below (see attached) shows the measured magnetization against temperature at room pressure for the material Gd and for another material for use in a magnetic refrigerator at room ...
3
votes
0answers
110 views

Electrodynamics and induced EMF question [closed]

A very long straight wire carries a current I. A plane rectangular coil of high resistance, with sides of length $a$ and $b$, is coplanar with the wire. One of the sides of length $a$ is parallel ...
2
votes
0answers
260 views

Hall effect with similar positive and negative carriers?

The Hall effect includes the transverse (to the flow of current) electric field set up by the charges which accumulate on the edges, to counter the magnetic component of the Lorentz force acting on ...
2
votes
4answers
398 views

Electromagnetic field tensor via tensor products?

Can the electromagnetic field tensor be thought of as the tensor product of two physically reasonable vectors? Are the vectors arbitrarily constructed so that their components simply give the values ...
1
vote
0answers
480 views

Current flowing through a square loop - Magnetic Field [closed]

A square conducting loop of wire of side $2a$ carries a uniform current I. Calculate the magnetic field at the centre of square due to the current in the loop.
3
votes
0answers
59 views

Charge distribution and potential in a 1-dimensional quasistatic system

Suppose you have an 1-dimensional system with a charge distribution $\rho(x)$ (not given) moving with an speed $v(x)$ (not given), calculate the potential $\phi(x)$ and the charge distribution ...
5
votes
0answers
88 views

Is there any antenna with a single null?

If we designate the origin (the reference point from which all displacement vectors are measured) $\vec{0}$, and If we consider a sphere $\mathbb{B}\left(\vec{0},\mathcal{R}\right)$ of radius ...
2
votes
3answers
406 views

Equivalent circuit for an arbitrary receiving antenna

This Wikipedia entry tells me that the Thevenin equivalent circuit for an arbitrary receiving antenna on which an electric field $E_b$ is incident is a voltage source $V_a$ in series with an impedance ...
1
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0answers
58 views

Lorentzforce and righthand rule [closed]

Figure 1: A spool is hung on a spring. A part of the coil hangs in front of a homogeneous magnetic field. The coil is incorporated in an electrical circuit. See Figure 1. the coil ...
5
votes
1answer
112 views

Metric of following spacetime and refractive index

Let's have metrics $$ ds^{2} = f(\mathbf r)dt^{2} - h(\mathbf r )\delta_{ij}dx^{i}dx^{j}. $$ Hot to show that motion of light in spacetime with this metrics is equal to motion in continuous media with ...
1
vote
1answer
77 views

Why is th $\hat{r}$ component zero in this integral?

I'm trying to evaluate the magnetic field by calculating the Coloumb integral $\overrightarrow{A}$, and later I will take: $$\overrightarrow{B}=\nabla \times \overrightarrow{A}$$ However, in the ...
1
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0answers
67 views

how does graphene affect the refractive index of an optical waveguide?

Could someone help me find data on the electro conductivity of graphene and its effect on the refractive index of an optical waveguide
1
vote
1answer
82 views

Power and magnetism

If we have a solenoid and a magnetic field passes through it, a DC voltage will be produced in the wire. If we want to calculate the power, we find out the current using Ohm's law. I know there is ...
1
vote
1answer
229 views

Do electromagnetic fields interact with air pressure?

I would like to know whether electric and magnetic fields interact with air pressure. Do changes in magnitude or direction of such fields increase or decrease the air pressure in a given volume of ...
1
vote
1answer
64 views

Determining the limits of an integral

In Griffiths' Introduction to Electrodynamics, Problem 1.28 (the triangular prism question) is especially challenging for me. I do not know how the limits of x are 0 to (1-y). My concern is the ...
1
vote
2answers
2k views

Ampere's law on a long wire with varying current density [closed]

On a question from my book: A long straight wire with a circular cross section of radius $R$ carries a current $I$. Assume the current density is not constant over the cross section of the wire, ...
2
votes
0answers
50 views

Is the electrical signal delivered to a load by a receiving antenna always $\propto \frac {\partial}{\partial t}$ of the $\vec{E}$ or $\vec{B}$ field?

A time-varying $B(t)$ field through a loop antenna induces a voltage proportional to $\dot{B}(t)$. A Hertzian dipole along a time-varying $E(t)$ field also induces a voltage across a load--while I ...
1
vote
1answer
178 views

How did neodymium magnets get their name?

Like in the question. Why neodymium magnets (Nd2Fe14B) are called "neodymium magnets"? Why not boron magnets? Or iron magnets?
0
votes
1answer
273 views

determining Induced emf/current through v x B . l

I am working on a question from my book. I am wondering how they conclude emf is negative in this case. looking at $$ \mathcal{E} = \vec{v} \times \vec{B} \cdot \vec{dl}$$ If there's some implied ...
0
votes
2answers
84 views

How do magnets work in classical electromagnetism?

A charged particle moving in a magnetic field experiences a Lorentz force $F=qv\times B$. A charged particle in a electric field experiences a force given by Coulomb's inverse square law. But for a ...
1
vote
2answers
368 views

How to test cutoff frequency of IR filter on camera?

Modern cell phones seems to come with IR filters on their cameras. I want to do an experiment to figure out what wavelengths these filters allow to pass and which they block. How would I go about ...
-4
votes
1answer
332 views

Classical Mechanics - Equation of motion, Lagrangian, Newtons 2nd Law [closed]

I really don't even know where to start with this question. A particle with charge $q$ moving in an electromagnetic field is described by the Lagrangian $$L=\frac{m\mathrm v^2}2+\frac qc\mathrm ...
6
votes
2answers
2k views

Why does electromagnetic induction actually occur?

In my book, it is written that "An emf is induced in a loop when the number of magnetic field lines that pass through the loop is changing" (Faraday's law) I understand that whenever there is a ...
1
vote
2answers
1k views

What constitutes displacement current? [duplicate]

In the chapter electromagnetic waves I was introduced with the concept of displacement current inside a capacitor. Since the region inside the capacitor is a dielectric there is no charge carriers in ...
1
vote
1answer
274 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 ...
1
vote
1answer
58 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 ...
1
vote
0answers
103 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 ...
1
vote
0answers
94 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 ...
1
vote
0answers
56 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, ...
-10
votes
1answer
268 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 ...
-1
votes
2answers
222 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?
3
votes
3answers
475 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 ...
-7
votes
1answer
977 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 ...
0
votes
1answer
50 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 ...