Tagged Questions

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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36 views

Electromagnetic induction

How change in magnetic flux linked with a coil induces electromotive force in a coil . Also please explain this in accordance with faraday's experiment?
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2answers
116 views

Experiment which shows that Newtons third law is not true for magnetic forces

I am just reading David Morins "Introduction to Classical Mechanics". He writes about Newtons third law the following: It holds for forces of the “pushing” and “pulling” type, but it fails for ...
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0answers
25 views

Au, Ag nanoparticles plasmon peak position?

Is the interaction between metallic nanoparticles (~ 20 nm) and light in the UV-Vis-NIR range governed by Mie theory or by Rayleigh scattering theory? Where are the Au and Ag plasmonic peaks located? ...
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0answers
51 views

Momentum of capacitor in a uniform magnetic field

We are observing ideal, charged, parallel plate capacitor placed in uniform magnetic field parallel to plates. Whole system is at rest and isolated (we have forces that hold plates separated, but net ...
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2answers
2k views

Does gravity affect magnetism, vice-versa, or do they “ignore” each other?

I am suddenly struck by the question of whether gravitation affects magnetism in some way. On the other hand, gravity is a weak force, but magnetism seems to be a strong force, so would magnetism ...
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0answers
30 views

Constant Rayleigh Scattering Cross Section

in the Review of Particle Physics - Interactions of Particles with Matter, there is a plot that gives the cross sections for different interactions of photons with matter. One of them is Rayleigh ...
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1answer
19 views

The strength and control over the strength of electromagnets, correlation between the strength and weight of the magnets

I am currently working on a project that aims to use the attraction & repulsion between two electromagnets as an alternative to weights, from a physiotherapy and rehabilitation perspective to help ...
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2answers
853 views

What does it mean when physical theories are inconsistent?

I am hoping that someone can explain in layman terms why Newtonian mechanics and Maxwell's equations are inconsistent. Wikipedia says that this inconsistency is what led to the development of ...
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1answer
34 views

Thermal emission cathode electron velocity distribution

I can't find any experimental data (or theoretical expression) on what is the velocity (or energy) distribution of thermal emission cathode electrons emmited from the cathode at approximately 2000 K ...
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1answer
71 views

Why is the Ohm's law $j=\sigma E$ accurate?

Ohm's law $j=\sigma*E=\frac{Q}{A}*\frac{F}{Q}=...?$ $j=\rho*v$= $\frac{q}{V}*\frac{s}{t}=\frac{1}{A}*I$ So why is $j=\sigma$E
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1answer
71 views

Tensor notation

I'm trying to understand the Maxwell Stress tensor notation. I'm given that each element in the tensor is given by ...
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0answers
66 views

Why is area considered and not volume to find the force of a solenoid?

I am doing a project involving solenoids. I found multiple websites that say the force (in N) a solenoid exerts on a soft iron bar as it enters the coils can be given by the equation ...
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4answers
155 views

Application of Kirchhoff's laws in circuits with inductors

As we know,the Kirchhoff circuit laws are applicable for conservative electric fields. Now it is applicable for circuits where inductors are present but the field there is not conservative. So how ...
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0answers
80 views

Energy of moving capacitor

On the following link were a discussion about energy in capacitor moving parallel to its field: Where's the energy in a boosted capacitor? My question is what happen if capacitor is moving ...
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0answers
24 views

Is there any simulation program for electrostatic and magnetostatic fields? [duplicate]

please can any one suggest me a good program for simulating electrostatic and magnetostatic fields (forces,flux density, energy and potential) ?
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2answers
57 views

DC Generator with magnet as rotor

DC generators convert the AC current in them by split ring commutators right and the graph of the current will be like this but the question is how would be the graph if the magnet is the rotor and ...
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0answers
19 views

Strength of Magnet in Magnetic Bearings

While reading about magnetic bearings, one reads about passive/active magnetic bearings. By passive, one means no electric current is put into the bearing for attaining magnetic levitation/flux. In ...
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1answer
35 views

Direction of EMF

I was reading electromagnetic induction and came across EMF.Now in my text book as the theory has been developed ,they have many a times talked about direction of EMF. But they have not clearly ...
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2answers
27 views

Possiblity of predicting behavior of system when properties described as functions over space?

Suppose I am given a system that consists of a distribution of charged particles(which are all over space and are point-charges). They are described by a set of functions instead of variables. These ...
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1answer
44 views

Can someone please explain impedance matching and wave reflection?

I'm reading Wikipedia's article on impedance matching (http://en.wikipedia.org/wiki/Reflections_of_signals_on_conducting_lines) and this just seems so foreign to me. 1) What does it mean for a ...
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2answers
91 views

Differentiating the Hamiltonian Operator, $\hat{H}$

Firstly let $\hat{H}$ denote the full energy of the electromagnetic wave. I'm trying to differentiate the Hamiltonian operator with respect to the components of momentum, i.e. $$\frac{d}{dp_x} ...
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1answer
24 views

Permeability and magnetization of soft iron at various fields

I'm curious as to the magnetic permeability of soft iron (and other materials if available) under different fields. I know permeability of materials changes with field (that is why we have saturation ...
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0answers
28 views

diamagnetism in constant magnetic field

"The diamagnetic materials repel the materials which produces magnetic field, so putting these materials in the proximity of the magnetic field generating materials produces the effect of the ...
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0answers
25 views

Heavyside Lorentz units and Gaussian units

What is the relation between Heavyside Lorentz units and Gaussian units? From this Wikipedia article, I noticed there are $4\pi$ difference between them, but my TA wants more. Is there other ...
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1answer
19 views

Finding the direction of several radio beacons using a faraday cage and a radio receiver

I'm trying to build a system that can detect the direction of a set of radio beacons operating on the same frequency. In order to do this I have planned to use a normal radio antenna placed inside a ...
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2answers
219 views

Has magnetism been experimentally demonstrated at the quantum level?

I've learned that magnetic fields are generated by electric currents, and that electric current is the motion of electrons and stuff like that. Many textbooks also talk about "point charges" and have ...
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0answers
27 views

Quantized modes of EM field in a cubic cavity

I am trying to solve for Electric field modes in a cubic cavity with perfectly reflecting walls. I know that for the modes, I have the standard Helmholtz Equation $$(\nabla^2+k^2)E_i=0$$ And I want ...
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0answers
50 views

How to calculate the Induced Voltage Given Spinning Conducting Loop? Intro to Electromagnetics problem [closed]

I'm having trouble figuring out a different variation of this problem. On my homework, I'm asked to find the induce emf for the following B field: $$\vec{B}=50\vec{a_y}$$ I was able to figure out the ...
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1answer
30 views

What is the easiest way to demonstrate low magnetic flux NMR on the bench?

I'm trying to build my own low fux density bench NMR set-up, and am well-versed in electronics. Continuous Wave is supposed to be the easiest. I see commercial instruments that stimulate elements in ...
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1answer
92 views

Electromagnet force equation clarification

So, from a previous previous question, I know what plane the force from an electromagnet will affect a ferromagnetic material in. I thought that would be enough, but working through some problems ...
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2answers
99 views

Relationship between surface density and volume density

Often in an E&M problem, I'm having to "chop" an extended object into an infinite sum of smaller extended objects which I know more about to find a potential or electric field or whatever. The ...
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1answer
48 views

How to calculate current flowing down a wire connecting charge to ground

If charge Q is connected to ground through a wire, how would you calculate the current that flows as a function of time? No other information is given. I have not seen this type of problem in the ...
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0answers
27 views

Frequency dependence of refractive index $ n $ considering electron oscillator using Electromagnetic Theory

First and foremost, I am referring to Hecht, Zajac E. Optics 4th edition. I am reading the dependence of refractive index on frequency, and it goes well until Hecht jumped on his equation. First we ...
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0answers
24 views

Deriving Ampère's Circuital Law from Ampère's Force Law?

Ampère's force $d^2\vec{F_{21}}$ of current element $i_2d\vec{\ell_2}$ on $i_1d\vec{\ell_1}$ is$$d^2\vec{F_{21}}=-\frac{\mu_0}{4\pi}i_1i_2\frac{\hat{r}}{r^2}\left[2(d\vec{\ell_1}\cdot ...
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0answers
47 views

Does a conducting wire give off measurable radiation?

In the Drude model (semiclassical, but should still apply here I think), the conducting electrons are in a constant electric field, and, in between collisions with the lattice ions (that happen, on ...
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3answers
59 views

Transformers and DC voltage

Ok, if I have a transformer with 100 coils of the primary and 200 coils on the secondary and I connect a 9 volt battery to the primary, how many volts should I expect from the secondary coil? I know ...
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2answers
515 views

Is there a relationship between the energy of a photon and the energy of an electromagnetic wave?

If the energy of a photon $E_{p}=hv$ And the energy of an electromagnetic wave is $E_{w}\propto \hat{\mathbf B}^2$ What is the relationship between $E_{w}$ and $E_{p}$?
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1answer
56 views

Would a simple electric generator based on magnetic induction( magnet moving near coils to produce current) work in vacuum?

Would a simple electric generator based on magnetic induction( magnet moving near coils to produce current) work in vacuum? I mean if that generator would be connected to battery to charge it - moving ...
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1answer
30 views

Estimating the rotational speed of DC motor

What is the best strategy to roughly estimate the RPM of a simple DC motor as seen in this video?. I want to estimate the max possible rotation of the coil that has $n$ number of turns and has moment ...
2
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1answer
184 views

A James Clerk Maxwell Disproof

One of my favorite physicists to learn about was James Clerk Maxwell, for the fact that he unified the study of E&M in physics and he would often disprove theories that did not work as a ...
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2answers
38 views

Net Electrostatic Field inside a Conductor is $\vec{0}$

I've heard an explanation for this, and my professor wasn't really able to clarify my questions, so I was hoping someone could help: Suppose there is an electrostatic field $\vec{E_{net}}\ne\vec{0}$, ...
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1answer
34 views

Conditions for characterizing a wave as plane wave

Given a wave equation, say for example $\Psi(x,y,z,t) = a \cos\left(\omega t -\vec{k}\cdot \vec{r} \right)$, what conditions should be met for $\Psi$ to represent a plane wave?
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3answers
74 views

What is the relationship between $V(t)$ and $V(x,y,z)$

I was recently asked this by a friend. He told me that coming from a physics background, he does not understand $V(t)$ and he believes it is purely theoretical construct made up by circuit ...
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1answer
38 views

How similar is comparison between the principle behind Newton's Cradle versus AC Current moving down a transmission line?

Anyone who has taken high school physics has seen the following assembly. You drop one ball from the left hand side and the ball from the farthest right hand side gets knocked away. This is to ...
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3answers
250 views

Why can't electrons fall into the nucleus?

I read a book on pop sci book on quantum mechanics and the author said that electrons do not fall into the nucleus due to quantum mechanics- which principles suggest this (I think it was Heisenberg's ...
2
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1answer
55 views

Electric charge of light? [duplicate]

Light (or any radiation as a matter of fact) is an electromagnetic wave so why doesn't it have a electric charge associated with it? As far as I know only static or flowing electric chargers can ...
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2answers
89 views

Non-stationary capacitor

A common exercise in non-stationary electromagnetism is to find the electric and the magnetic field generated by a capacitor with round plates, if the potential difference between the plates varies in ...
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2answers
107 views

Physical meaning of imaginary part of Electric field?

As far as I know (or I thought I knew), if we have an electric field $$\mathbf{E}=\mathbf{E_0}\cos(\omega t - kx),$$ we can define it as the real part of $$\mathbf{E}=Re(\mathbf{E_0}e^{i(\omega t - ...
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1answer
470 views

Has NASA confirmed that Roger Shawyer's EmDrive thruster works? [duplicate]

This article states: But somehow, despite all of the reasons it shouldn’t work, it does. Scientists at NASA just confirmed it. Now in this question - it is strongly suggested that this ...
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0answers
47 views

Remote EEG Detection / Reading

I recently noted that Phillips, Accenture, and Emotive grouped together to create a proof of concept that would assist ALS patients to gain greater control of their lives through brain, voice, and eye ...