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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152 views

How do two electrical charged particles know to repel or attract each other?

Now per QED, electrical charges interactions are effected by photons. Suppose you are one of the two charges. How do you know to attract or repel the other charge? In other words, how do you know if ...
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0answers
25 views

Ground influence on 434 MHz radio signal

I have read in a paper that ground acts as reflector for radio signals in 434 MHz band. Why is that the case?
10
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3answers
635 views

Electromagnetic waves should stop while encountering a conducting shell?

I am a high school student who has just started reading elementary electromagnetism and am a completely beginner in this subject. I have read in books that EM waves are nothing but sinusoidal ...
2
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1answer
37 views

FDM versus fdtd for computational electromagnetics

Every article I've seen on computational electromagnetics uses the Yee fdtd algorithm, and I'm wondering if would be possible to do the same analyses using out of the box FDM with more data points, ...
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0answers
15 views

How can you relate magnetic dipole moment using bound current density?

This was on my midterm last week, the question ask us to use bound current density to compute magnetic dipole moment
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38 views

Does the total energy in an electromagnetic field depend on the acceleration of the sources?

If I accelerate a charge from rest to some velocity $\vec v$, does the total final electromagnetic energy contained in the field depend upon the acceleration of the charge?
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2answers
83 views

Why doesn't the electron lose or absorb energy while remaining in a selected orbit? [closed]

Postulate 2: When an electron revolves in any selected orbits, it neither emits nor absorbs energy . The energy of an electron in a particular orbit remains constant. Thus, Bohr, by postulating ...
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1answer
53 views

What are the boundary conditions for EM waves normally incident on the interface between two dielectric media?

An EM wave, amplitude $E_0$, frequency $\omega_0$, is incident upon a material with relative permittivity (dielectric function) $$\varepsilon \left( z \right) = \left\{ \begin{gathered}{\varepsilon ...
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0answers
24 views

Construction of a magnetic dip “compass”

I want to make a demo magnetic dip compass and was wondering what would be the relative sensitivity (restoring torque) of: 1) two neodymium magnets at the ends of a plastic rod (say 40 cm. i.e. ...
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1answer
65 views

Electromagnetic field or direct interactions between charged particles?

Consider a small distribution of charged particles enclosed by an arbitrary volume $V$ with boundary $S$. It can be shown that the total mechanical momentum of the particles, $\mathbf{P_{mech}}$, ...
0
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1answer
40 views

Closed and Open Electromagnetic Cores

I think I may understand this concept, but I haven't been able to verify with anyone that I'm going about this the right way. So when a wire is wrapped around a core that is a closed loop, like a ...
1
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1answer
115 views

Why doesn't an electromagnetic wave violate conservation of energy?

I'm starting to study electromagnetic waves and as i understand, an electromagnetic wave projects a varying electric field. This electric field can in turn give forces of repulsion/attractions to the ...
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2answers
63 views

Why does freshwater attenuate signals less than seawater?

One of the most interesting problem in underwater communication is how deep the device (i.e. submarine) could go to still be able to communicate with on-shore data centers. The attenuation in a ...
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0answers
35 views

Is there an equivalent force to magnetism for gravity? [duplicate]

In electrodynamics, one way to explain the origin of the magnetic field is to analyze how a moving particle perceives a static electrical field under the effects of special relativity. Due to the ...
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0answers
36 views

Larmor Precession of a macroscopic number of electrons

I know that there are some similiar questions out there, but I'm still quite puzzled by the following problem. Say i have a box full of interacting electrons ( I'm not sure if it would change anything ...
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0answers
10 views

Tunable ferroelectric material

Is there any tunable ferroelectric (whose permittivity changes by applying electric field) material for visible or near IR applications?
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2answers
45 views

What does it mean to say “a paramagnetic material is attracted to an external magnetic field?”

I'm just having a hard time wrapping my head around what actually goes on when a paramagnetic material is exposed to an external magnetic field. I understand that the individual dipoles line up so ...
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0answers
31 views

Is there an analytical expression for the conductivity of the surface of topological insulators?

I have a question about the conductivity on the surface of Topological Insulators (TI): Is it accurate to model the conductivity by the Drude model (I read a paper that modeled the conductivity with ...
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3answers
129 views

Rigorously prove that electric field is zero in a perfect conductor

I have ran into a problem while trying to prove that the electric field is zero in a perfect conductor My argument went something like this: We know that: $$\vec J = \sigma \vec E$$ In a ...
2
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4answers
79 views

How do radio waves reach receivers without being canceled out by interference?

When I think of waves traveling through a medium, I tend to think of the double slit experiment or waves in a pond. In those cases, waves are canceled out by destructive or constructive ...
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0answers
62 views

Ohm's Law for Accelerated Conductors

My questions are about the Ohm's law for a moving conductor in a stationary magnetic field. As we know this law is stated based on following relation with respect to the fixed frame of reference ...
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0answers
19 views

If an common metal is induced with a static dipole moment, won't the the positive side be weaker?

To my knowledge, common metals with metallic bonding is formed through free electrons within its lattice structure. If say we are to shift the free roaming electrons to one side and therefore minutely ...
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0answers
22 views

Induced EMF of a fixed wire?

I've studied many examples where there is a "moving" conductor passing a magnetic field or in a magnetic field, or a moving magnetic passing a solenoid or conductor, and the induced $\epsilon$ is ...
1
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1answer
77 views

Moving frames - a blow on “virtual particles”?

There is a polemic about whether virtual particles EXIST, or are only a tool for making our calculi easier. Here is a doubt about their existence, and on the other hand, an argument in support of ...
5
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1answer
106 views

What is the Poynting vector of an electron?

On chapter 27 of "The Feynman Lectures on Physics Volume II: Mainly Electromagnetism and Matter", Richard Feynman says: Finally, in order to really convince you that this theory is obviously nuts, ...
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2answers
58 views

Why does $\hat n \times (\vec E_1 - \vec E_2) =0 $ imply that the tangential electric field components are equal?

On page 8: http://local.eleceng.uct.ac.za/courses/EEE3055F/lecture_notes/2011_old/eee3055f_Ch4_2up.pdfele I don't understand why $E_{t1} = E_{t2}$ is equivalent to $\hat n \times (\vec E_1 - \vec ...
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0answers
21 views

Standing Wave ratio vs frequency in power transmission lines? [migrated]

What is the relationship between Voltage Standing Wave Ratio (VSWR) and frequency in context of transmission power lines?
6
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2answers
84 views

Why the extra term $\frac{1}{2}(\partial_{\rho}A^{\rho})^2$ in the photon Lagrangian?

In my quantum field theory class we have been told to use this Lagrangian for the photon field $$\mathcal{L}=-\frac{1}{4}F_{\alpha\beta}F^{\alpha\beta} -\frac{1}{2}(\partial_{\rho}A^{\rho})^2.$$ but ...
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0answers
22 views

Question on electromagnetic field tensor

if few particles are being accelerated in electromagnetic field and the field tensor is $F^{\mu \nu}$, and also if the acceleration of the particles are given (or known), then how to prove that we ...
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1answer
46 views

Forces on moving charges

I want to know what are the total forces on a moving charge due to another charge. I heard that moving charges is the cause of all magnetism.So what I think is that if we have a charge in motion ...
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1answer
50 views

Is the overall force of a test charge in a electromagnetic field always the same?

I had a conversation with my physics teacher today about electric fields and he told me something I couldn't believe and because I found no information elsewhere I am going to ask you guys. Imagine a ...
0
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1answer
23 views

Has a “phase” change ever been considered between RF radiation and photons [closed]

Where photons have properties such as spin and line of sight propagation, radio frequencies do not to the same degree, Photoelectric effects are attributed specifically to photons but not to radio ...
0
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2answers
53 views

Why can't unequal current sources be connected in series?

Imagine two power sources, PS-1 that can supply $5A$ at $100V$,and PS-2 can supply $10A$ at $40V$, due to conservation of charge, and Kirchoff's current law(KCL) this is incorrect, and would lead to ...
2
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2answers
128 views

How does the Lorentz force work?

How does the Lorentz force work? In the context of a homopolar motor. I am a year 13 student so please keep your answers simple! I am having trouble understanding the Lorentz force; does the magnetic ...
2
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2answers
457 views

Why do old transformers make sounds, but new ones don't?

What I think is that maybe insulation is gradually removed between plates, and eddy currents start passing from one plate to another and this produces sound. Am I right?
3
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5answers
77 views

Can a Coronal Mass Ejection (CME) cause a blackout on Earth and why?

Can a Coronal Mass Ejection (CME) cause a blackout on Earth and why is it so what's the relation between electro magnetic radiations and electrical and electronic appliance.what exactly does it do to ...
0
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1answer
31 views

Does zero free current entail zero $\vec H$?

There are two kinds of magnetic fields (different authors give them different names), $\vec B $ and $\vec H$ which are related by the equation $$ \vec B = \mu_o (\vec H + \vec M)$$ where $\vec M$ is ...
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3answers
113 views

Do mobile phones produce radiation harmful to humans? [closed]

What are the health effects of mobile phone radiation (if any)? Does using a mobile phone without an SIM card change the answer?
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2answers
104 views

How come Wifi signals can go through walls, and bodies, by kitchen-microwaves only penetrate a few centimeters through absorbing surfaces?

The only difference that I know of between Kitchen Microwaves and Wifi signals is how much power is pumped through them. Why is it that Wifi signals, being 1000 times weaker can travel so much ...
4
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5answers
386 views

Faraday's paradox

I have studied that Faraday's law of induction and motional emf are two different lines of thinking but are essentially same. But then, how can Faraday's paradox be explained by Faraday's law of ...
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1answer
68 views

Biot-Savart and Amperes law inconsistentcy

Imagine the situation below where a steady current $I$ goes through the line. The radius of the semicircle is $r$. How do I compute the magnetic flux in the point $P$, marked by a black dot? ...
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2answers
41 views

Does the power weakening of an electromagnetic transmission over distance depends on the beam's width?

Does the power weakening of an electromagnetic transmission over distance depends on the beam's width? If I emit an omnidirectional electromagnetic transmission, its power weakens in the ratio of ...
0
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1answer
18 views

Why does material change electrical property based on frequency of input electrical signal?

I was investigating whether dry soil would conduct electricity. What I found was that at 60 Hz frequency (i.e. power line fell to the ground), dry soil is a very good conductor. But if you increase ...
1
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0answers
18 views

Mixing liquids when applying a voltage

I'm thinking in the following experiment: A) Two (non mixable (like water and oil)) liquids are going to lie in a container, in the extremes of the container there are two electrodes, those ...
2
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2answers
62 views

Electromagnetism in astrophysics

What is the most important electromagnetic phenomena involved in astrophysics?, I am working in a presentation of magnetars, pulsars and magnetic field of planets and I would like to know if there are ...
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2answers
77 views

Momentum conservation in an electromagnetic system?

Suppose that I have two charged particles in the configuration below. Let us assume the following: We apply a constant force $f$ to the the bottom particle so that it has a constant acceleration ...
0
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2answers
55 views

Is there any theoretical reason behind multiplying by $N$ when using Faraday's law of induction?

It is a well known fact that whenever we want to calculate the emf in a solenoid we usually multiply the changing flux for one loop times $N$, which is the number of turns in the solenoid. But why is ...
3
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2answers
145 views

Challenging Magnetostatics Problem - the “blind spot” of a magnetic dipole

I'm reviewing for an electromag exam and I stumbled upon a problem that's really hard to figure out. Here it is: A small magnetic dipole with moment $\vec m = m_o \hat z$ is in a region with uniform ...
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1answer
37 views

Can I tear apart a pipe with magnetostriction? And how big field should I use?

As I know, with magnetostriction we can "stretch" its unit cell. The stronger is the field, the more it expands the cell. Using alternating current in coils that induce magnetic field we can stretch ...
2
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0answers
103 views

Stress Energy Tensor of EM Field

Stress energy tensor for electromagnetic field is given by $$T^{\mu\nu}=\frac1{4\pi}(F^{\mu\alpha}F^{\nu}{}_\alpha-\frac14 g^{\mu\nu} F_{\alpha\beta}F^{\alpha\beta}).$$ My textbook (unpublished ...