Questions tagged [electric-fields]
For questions that utilize the concept of electric fields (commonly denoted by the letter E), or for questions whose answers likely involve electric fields. More specific than the [electricity] tag, as questions about the phenomenon & theory of electricity do not necessarily involve the discussion of fields.
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How to correctly use Gauss Law? Why is it used the way it is?
Gauss Law
$$\oint \vec E . d \vec A = \frac{Q_{enclosed}}{\epsilon _○}$$ From this question, Gauss Law is more fundamental than Coulomb's Law. This seems counter intuitive to me when it comes to ...
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Confusion about energy transport in a circuit
I have some confusions about how to imagine energy flow in a circuit. Imagine for example just a simple circuit with a battery, two wires and a light bulb.
According to classical Electrodynamics the ...
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What are some ways to derive $\left( \boldsymbol{E}\cdot \boldsymbol{E} \right) \nabla =\frac{1}{2}\nabla \boldsymbol{E}^2$?
For each of the two reference books the constant equations are as follows:
$$
\boldsymbol{E}\times \left( \nabla \times \boldsymbol{E} \right) =-\left( \boldsymbol{E}\cdot \nabla \right) \boldsymbol{E}...
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Why is $\nabla \cdot E = 0$ for outside a charged sphere? [closed]
It seems contradictory to Gauss's Law saying $\nabla \cdot E = \rho /\epsilon$
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What is the oil charge? [closed]
The chargers in this question are fixed I don't understand how to approach this problem.
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Is the net charge in the interior of a conductor zero even when the total net charge (including the surface charges) is positive?
In the textbook Matter & Interactions by Chabay and Sherwood (chapter 14.6), they say
...any excess charges on a piece of metal, or any conductor, are
always found on an outer or inner surface. ...
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Explanation of $\vec{\nabla} \times \vec{E}=-\frac{\partial \vec{B}}{\partial t}$ [closed]
If we have a static charge distribution, then $\vec{\nabla}\times\vec{E}=\vec{0}$, what if we now let that charge distribution to move with a constant velocity, how is this gonna affect the curl of ...
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How can we choose a coordinate system to calculate the field strength E [closed]
We have two infinitely long strings charged with a linear charge density λ and -λ, separated by a distance l. The electric potential at a distance r from the center of the strings (r>>l) at an ...
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2
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What will be the path of this particle in combined electric and magnetic fields?
Say a particle is moving with constant velocity along the positive y-axis. Both electric and magnetic fields are applied along the positive x-axis. What will be the path of this particle?
I am ...
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Force on a dielectric medium
Under the influence of an external electric field the dipoles in a dielectric medium arrange themselves. These dipoles will create a field that opposes the external field, resulting in a net field ...
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Electric flux through a square surface by a charge kept above it [closed]
A charge $q$ is placed at shown at a height $a$ above the center of a square surface of side length $a$. I have to find the flux due to $q$ through the surface.
I do not find any symmetric shape about ...
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Can the time varying Intensity of an electric field of a wave be measured?
Lets say that we have a detector which we use to measure the intensity. Theoretically, the intensity is a varying function of time (When we calculate the Poynting vector) but often in textbooks they ...
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Is the electric field actually perpendicular to the ends of a gaussian cylinder here? [closed]
In this problem from Griffiths', the field at the ends of the cylinder is taken to be only normal to the ends and it is said that "symmetry dictates that E must point radially outwards". Can ...
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Constant currents do not interact with static charge. Why is that?
I'm trying to figure out why the Jefimenko equations are not usually written in terms of 4-vectors. If they are fully relativistic, why not show it?
These are the equations:
So, the electric and ...
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Distribution of charge in uniform hollow sphere
In electrostatics we learn that if we put excess charge in a hollow sphere, the charges eventually get distributed on the surface uniformly. But there is one thing I don't understand: hollow sphere ...
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Why does an charge free space always create an oscillating field?
My question is on the nature of oscillating electric field. From Maxwells equation, we know that the solution of the electric and magnetic field for an empty space are always oscillating fields. I ...
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When exactly does a change in $E$ or $B$ result in an electromagnetic wave?
I am always wondering why only accelerated charges emit electromagnetic waves, while constantly moving ones do not.
I imagine an electron in else empty space moving with speed $v$. The $E$-Field in a ...
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Why Magnetic Field doesn't annihilate itself?
Reasked, edited
Note: I don't get why it is not a good question according to some people, but as far as I can say it is well posed. If usefulness is of matter, the question is about why zero energy ...
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Is it true to say that there is a single electric field and it is inhabited by and affected by all charges in the universe? [closed]
I don't see why or how this could be argued against or if it really matters, but that's why I ask the forum.
I am just trying to understand the nature of the fields in the universe. Am I correct in ...
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1
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33
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How to choose correct gaussian surface?
Suppose a undisturbed charge of magnitude +q at a certain place in the plane and then consider a point 'p' at a distance r from the charge. To calculate electric field at point 'p' we decide a ...
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Do the molecules inside a dielectric physically move when the dielectric is polarized by an external electric field?
Today a colleague and I had a heated debate over whether, when an external electric field is applied across a dielectric, the molecules in the dielectric actually move/rotate (flip to align with the ...
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Energy transmission from opposite magnetic field vectors. A wire with a current in a homogenous magnetic field
This is my first post and also the first time I've ever tried understanding a physics concept by approaching it with my own math logic so tips on trying to do this more effectively are also welcome
I’...
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Why do charges outside the closed Gaussian surface not matter for the flux in the event they end inside the surface?
I think I am misunderstanding something elementary. Supposing a scenario where you have a negative charge enclosed in a Gaussian surface, why would the presence of outside charges not affect the flux?
...
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Is it possible to sustain an net electric charge density in a moving conductor? (MHD application)
The conservation of electric charge, deduced from the divergence of the Maxwell-Ampère equation, takes the form:
$$ \nabla \cdot \textbf{J} = -\frac{\partial \rho_e}{\partial t}.$$
For low frequency ...
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Why is there plasma near the inlet when Voltage is increased to higher Voltage? What can I do to eliminate this?
We built this plasma jet reactor with a side inlet of helium at 2 slm. My question is why is there plasma generated near the inlet where in it should only be at the bottom part. You can check the ...
4
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1
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727
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Doubt regarding an assumption made in an example in Griffiths
In Griffiths' Introduction to Electrodynamics, example 14 in chapter 7, "Electrodynamics." He makes an assumption/claim that I don't understand the reason behind, or don't agree with.
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2
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How many dimensions are in the electromagnetic field?
This question asks how many dimensions there are in the electric field for the purposes of better understanding polarization. However, the other answers don't seem to fully address the question, and ...
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1
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Confusion regarding field density
In my query, I'll be discussing a test charge and I'd appreciate any responses
My doubts stem from this statement and might involve misinterpretation of it
"Since the magnitude of B is 10T, ...
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1
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26
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What is the electric field due a charged conducting sheet and a charged conducting plate in terms of $σ$ and $ε°$? [closed]
I am getting it equal to $σ/2ε°$ for a conducting sheet and $σ/ε°$ for a conducting plate. Am I right? If yes then explain it to me why is it so?
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How do you visualize an electro-magnetic wave?
How do you visualize an electro-magnetic wave? If there is a very narrow beam (like the one produced by may be a maser?) confined within a few centimeters (in its wave-front) with amplitude say x, ...
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What type of things create electric fields? [closed]
Magnets create magnetic fields, but what creates electric fields? If this question is too broad, I can elaborate as much as people want.
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Unexpected generation of plasma far from HV rod electrode. Why is plasma being generated near the encircled part wherein there shouldn't be?
we have built a kHz jet plasma reactor and we are generating plasma at the inlet side every time we increase input voltage to more than 3 kV. Working gas used was argon at 1 slm entering at the side. ...
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Electric field is produced by the changing magnetic field and not by charged particles according to coulomb's law or Gauss's law?
In my physics textbook, Concept of physics by H.C. Verma, in the section on "Induced electric field", the statement below is written (p. 291):
Electric field is produced by the changing ...
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Is electric field inside a conductor really always zero?
The standard explanation in textbooks goes that in the presence of electric field (e.g. external electric field) the free electrons inside the conductor will keep moving until electrostatic ...
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3
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Can an Electric and Magnetic fields be non-perpendicular? [duplicate]
Can an Electric field and a Magnetic field be non-perpendicular to each other$?$ If yes, can an electromagnetic wave pass through that region$?$
I think that yes, both can be non perpendicular to ...
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3
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Can the $E$ field exist without any $B$ or $H$ field?
I'm trying to understand basic electrodynamics at a fundamental level. It's very confusing. I have heard that there are only four forces: gravity, EM, and two nuclear forces. So it appears that the ...
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Relativistic correction of Coulomb's Law
I am attempting to describe Coulomb's law but with the delay one would get because of the light speed limit. I am aware one could do that using Maxwell's equations because they are relativistic, but ...
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Is there a potential difference produced across the ends of a circular conductor ( eg. a disk) that is translating across a uniform magnetic field
Im not necessarily talking about emf (and also not considering rotation) , but rather the potential difference created due the induced electric field to balance the lorentz force on the electron. For ...
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2
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Why do electric field lines bend towards the normal of a linear homogeneous dielectric sphere?
Why do the field lines of the uniform external field bend towards the normal of the linear homogeneous dielectric sphere as shown in the diagram?
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What exactly is induced electric field, Is it present only in conducting loops? [duplicate]
In my textbook it is written that : The presence of a conducting loop is not necessary to have an induced electric field. As long as $\vec B$ keeps changing, the electric field is present. If a loop ...
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1
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25
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Electric field at surface of uniformly charged bodies
If we have any simple object like sheet,rod or sphere with uniform charge at them, is electric field at surface always finite?
For sphere I read that it is finite because as test approaches the ...
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Coulomb field from QED
It is well-known how to obtain Coulomb's law in perturbative QED (e.g. the answers to this question on this site). I am trying to understand if there is any reasonable way to give a meaning, within ...
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3
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Electric field of an electron after it comes into existence
This is a followup of an older post I made here, whose main premise was not answered. Suppose than an electron is created in a scattering experiment, where other particles are created/destroyed in ...
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Real-life applications of non-uniformly charged line charge and ring of charge
The title sums it up; are there any practical examples of not uniformly charged line charges and ring of charge?
Line chargers: I know they are used in wire chambers for high-energy physics ...
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Corona Discharge, Leyden Jar and Free Charge [closed]
Watching Walter Lewin's 8.02x- Lect 14, at the end of it, he explains the mechanism behind a Leyden jar. The (simplified) picture is the following:
Source: https://www.youtube.com/watch?v=By2ogrSwgVo
...
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3
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Can we calculate electric field exactly at surface of charged sphere? [closed]
For a uniformly charged sphere, electric field at surface of a solid sphere is given as:-
$$E=\frac{KQ}{r²}$$ (if radius is r)
So did we actually calculate electric field at surface of sphere or just ...
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Electrical field in a circuit
This is a picture I found online:
I have two questions about this.
How do we know that over the power source and over the resistor, the electrical field is parallell to the power source or resistor. ...
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When is electric flux zero? [closed]
While studying about electric flux, I came across a problem which asked to calculate net electric flux through uncharged closed hemisphere. The answer was 0. But electric flux is amount of field line ...
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Electromagnetism: Electric field between a sphere and a concentric shell of different polarity
For a conducting sphere of radius $a$ and charge $Q$ surrounded by a concentric spherical shell of radius $b$ and charge $-Q$ (where $b > a$), I am aware that the electric field in the volume ...
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3
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Electric field beyond its simple definition of force per unit charge
I read this from Div, Grad, Curl and All That:
The second reason for introducing the electrostatic field is more basic. It turns out that all classical electromagnetic theory can be codified in terms ...
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