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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 [tag:electricity], as questions about the phenomenon & theory of electricity do not necessarily involve the discussion of fields.

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24 views

Electrostatic field-Field lines relationship

How is the $\frac{1}{r^2}$ dependence of the electric field due to a stationary point charge consistent with the concept of electric field lines?
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0answers
11 views

Electric field of a rod [on hold]

I'm kinda struggling with the following question, it will be really nice to get some direction in how to solve it: Find the electric flux through the (x,y) plane of a rod with a length L that is ...
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0answers
30 views

Work done against electric field [on hold]

If a charged body has $10^{-4}$ C charge and radius of $1 m$ then find the amount of work done against the elctric field in contracting the body for $0.5$ m radius. I am fed up with the question.I am ...
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1answer
52 views

Two types of electric field

My textbook mentions that electric field produced by electric charge and that produced by changing magnetic field are different in nature. After searching from various sources I found that electric ...
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1answer
16 views

Net flux through insulating cylinder

In a non-uniform electric field, say with field lines curving away from each other along x, will the net flux on a cylinder be negative or zero?
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1answer
62 views

Confusion relating to setting reference point to $r=\infty$

Consider the diagram given below. If I put my reference point at infinity, then I get different line integral values for paths in blue and red, and hence different values and yet the integral $E.dl$ ...
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1answer
25 views

Why is the electric flux of a point charge inside a sphere not 0 since its a vector and all the field lines point outward?

I know that the magnitude of the total flux of a point charge is $\frac{q}{ϵ_0}$, and can follow the maths and reasoning behind it. But since flux is a vector, shouldnt it also have a direction? I ...
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3answers
1k views

When does a vector component keep being a vector, exactly?

English is not my native language, so please forgive my errors. Consider this example: This is a classic: an exercise requiring you to calculate the electric field produced by a charged ring on its ...
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0answers
28 views

Grounded Conductor [closed]

The inside of a grounded spherical shell of radius $R$ is filled with uniform charge density $\rho$ and charge $Q$. (The density is fixed; it doesn’t "exit to ground".) What will be the electric field ...
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0answers
32 views

Calculate the electric field and potential given a potential difference [closed]

I have been asked to calculate the electric field and potential laws inside this coaxial cable: My first try was to apply the Gauss' Law between the two conductors, so if the battery charges the ...
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2answers
58 views

Electric Field Inside of a Conductor [duplicate]

I have seen many explanations for why the net electric field inside of a conductor is zero (assuming only electrical forces are acting on the particles inside of it). These explanations typically say ...
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2answers
36 views

Accuracy of Continuous Charge Distributions [duplicate]

In E&M, it is common to represent the charge on a body with a continuous, scalar charge density function. In reality though, the body contains discrete charges. I understand why this approximation ...
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1answer
35 views

“flowing” speed of an electric field?

Consider a capacitor made of two infinite plates which are at a very large distance $d$ from each other. We place a positive charge on a plate and a negative one on the other one. Two electrical ...
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0answers
20 views

Electric field between 2 parallel plate capacitor [closed]

a magnitude of electric field is given between parallel plate capcitor and a silver coin placed between it. find induced charge on both face of coin and total chage on both face. radius of coin is ...
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3answers
68 views

Why is the concept of electric field lines needed to understand electric fields? [closed]

I am recently learning about electric fields. So I encountered the concept of electric field lines. As they are not real but imaginary lines. Why do we need them to understand electric field? I am ...
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2answers
71 views

How can we argue $\nabla\cdot v = 0$ when ${\mathscr r} \ne 0$ on this vector function?

I am dealing with the vector field: $$v = \dfrac{\hat{\mathscr r} }{{\mathscr r}^2}$$ And I am studying its divergence. If we compute it we get: $$\nabla\cdot\left(\dfrac{\hat{\mathscr r} }{{\...
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4answers
49 views

Relationship between potential and electric field

There are a number of ways to solve this problem but was interested in doing it via the formula: $$ ∇V = -E$$ However the potential on the line due to -q is $$ \frac{-q}{4\pi\epsilon_0((0.5d)^2+y^...
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1answer
74 views

Can you electrically charge a black hole so that it would repel electrons?

Assume we somehow drop LOTS of electrons into a black hole, without the black hole accreting any other matter or energy at the same time. I suppose the charge of the black hole would build up much ...
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1answer
40 views

Gauss's Law and Superposition Principle [closed]

Hi I am doing the homework in MIT 8.02 by Dr.Lewin, I doubt that the answer provided online for Problem set is wrong, here is the problem. For question(a)(b)(c) it answers For me, I think the ...
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2answers
26 views

The image charge inside the conducting sphere without producing any electric field [closed]

In the method of images for a grounded conducting sphere, we calculate the position of image charge at $$\frac{R^2}{r}$$, due to which there should be an electric field inside the conducting sphere ...
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3answers
27 views

Field lines and flux

To my knowledge, flux of a vector field through a given surface is the integral of the dot product of vector field and a unit vector given to a surface element over the entire surface. Field line is ...
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1answer
63 views

Influence of an external electric field on an uncharged capacitor

Influence of an external electric field on an uncharged capacitor. Fig A shows an uncharged capacitor with no external electrical field. There is no net charge on each of the plates. Since the ...
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4answers
99 views

Does Electromagnetic wave propagation really use $E$ to create $B$

I was studying how electromagnetic waves (EM waves) were generated and propagated. I was shown a dipole antenna with an AC source sloshing charges back and forth. To my understanding, when the ...
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2answers
39 views

Magnitude of an electric field on a long rod [closed]

You place $2.7 \: \rm \mu C$ of charge along a long nonconducting rod. The rod extends from $x=0$ farther than you can see along the positive $x$ axis. The charge distribution has the form of a ...
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2answers
85 views

What is the unit vector in electric field formula? [duplicate]

What is the $\hat{r}$ (vector) in the formula $\vec{E} = k\frac{q}{r^2} \hat{r}$ for the electric field ? Why we dont use the vectors $\vec{i},\ \vec{j},\ \vec{k}$? Also why this vector doesn't ...
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2answers
29 views

Charge decay (leakage) of a charged metallic sphere

I have a spherical ball (charged to a specific charge) and the charge on the ball leaks to the surrounding. I observe that the charge on the ball reduces exponentially. Can anyone give a theoretical ...
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1answer
31 views

Floating potential of a conductor near another conductor with known potential with respect to the earth

Electrostatics textbooks delight at computing the electric field or the potential created by a known distribution of charge, ignoring the fact that this is rather a non practical question. In ...
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1answer
48 views

Flux density via Gauss' Law inside sphere cavity

There are many similar questions on here but most seem to deal conceptually with electric field, not the mathematics behind it. The setup is this: there is some sphere of radius b which has a volume ...
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2answers
33 views

Why do outside charges not contribute to net flux through a surface, pt 2

The question I have is a succession from the ones below. Why do outside charges do not contribute to net flux of a Gaussian Surface? Gauss' law and an external charge The responses to these ...
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0answers
23 views

Rotate counterclockwise from the +x axis? Linear charge density problem

So I have a homework question from earlier that I already got the right answer (not looking for anyone to solve), I just have more of a theory question with what "counterclockwise from the +x axis" ...
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1answer
26 views

Is there Electric Flux through a closed loop around a current wire?

In one of his lectures, Professor Walter Lewin is ammending Ampère's Law to include displacement current (i.e. It not only depends on the current that penetrates the loop, but also on the changing ...
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1answer
27 views

Electric field on the boundary of a continuous charge distribution

In Purcell and Morin's Electricity and Magnetism, 3rd Edition, the claim is made that the magnitude of the electric field on the boundary of a continuous charge distribution is finite (assuming the ...
2
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1answer
40 views

Is a constant electric field CP violating?

Consider, for instance, a fundamental massless three-form field $C_{\alpha\beta\gamma}$ in the Coulomb phase: $$ \mathcal L = E_{\mu\alpha\beta\gamma}E^{\mu\alpha\beta\gamma} + C_{\alpha\beta\gamma}J^...
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1answer
28 views

Field intensity for electric field and vector potential

In general, the intensity of an electric field is given by $$ I = \frac{c\epsilon_0}{2}E_0^2 $$ where $E_0$ is the peak amplitude of the electric field. Let's say we have an electric field $$ E(t) = ...
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0answers
21 views

Screening of the electric field in the Higgs phase

Dvali states in his paper on Three-Form Gauging of axion Symmetries and Gravity that “As usual, in the Higgs phase the electric field is completely screened in the vacuum,” and in another ...
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1answer
57 views

Torque on dipole in a non-uniform electric field [duplicate]

What happens when an electric dipole is kept in a nonuniform electric field?
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1answer
38 views

Can a strong electric field cause the electrons to come out of the atoms?

Can a strong electric field cause the electrons to come out of the atoms, is this how free electron are obtained in a discharge tube?
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1answer
51 views

Electric field lines properties

I wanted to ask a question. My question is that are the properties of field lines ( number of field lines leaving/entering a point charge is proportional to the charge, field strength between points ...
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2answers
32 views

Field strength at point using field lines

I have recently read that the electric field strength can be compared between 2 points from the relative field line density but I am having trouble in applying the concept. What I find confusing is ...
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1answer
55 views

Radial vs tangential component of electrical field due to dipole

I was wondering that why should the maximum magnitude (with respect to $\theta$) of radial component of electrical field of an electric dipole, $$E_r=-\partial V/\partial r=\frac{2p \cos\theta}{4\pi\...
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2answers
135 views

Proof that electrostatic self-force is zero

Suppose there is a charge distribution in region V and zero charge density outside V such that electric field goes to zero infinitely far away. How to prove that this charged body does not exert an ...
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0answers
44 views

Experiment interpretation. Dielectric polarization/triboelectricity/other?

My aim was to create a relatively strong electrostatic field to experiment with biological systems. So, I built a kind of "sandwich" made of a plate of aluminium surrounded by two 4mm plates of ...
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0answers
25 views

Is it possible to use laser-like technology to create effective force field?

By laser-like lechnology I mean a coherent ray of particals or waves with the same amplitude/energy. This ray would be emited on limited distance (lets say 2meters) where it will be absorbed by ...
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1answer
54 views

Electric field at center of a uniformly charged hemispherical shell [closed]

My attempt : I divided the shell into charged rings by whom I know the electric field at the center by the following relation : $\hskip2in$ Integrating the electric fields by all the rings I get ...
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2answers
32 views

Anomalous value of electric field due to a uniformly charged disc at a point on its central axis

Upon trying to find the electric field using integration (as done below) we get the following result : According to me there are two problems with this result : This function is not of odd parity. ...
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1answer
53 views

Boiling point of water in microwave oven

My textbook says that water heats so well in a microwave oven that people might be able to heat a cup of water as much as $8~C^{\circ}$ above the normal boiling temperature of water without causing it ...
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1answer
30 views

Surface charge of an infinitely long cylinder with uniform polarization

I have a polarization in form of; $$\vec{P}=k\hat{\phi}$$ And I want to find surface surface charges with $\sigma=\vec{P} \cdot \hat{n}$ I found two directions $\hat{r}$ and $\hat{z}$ for two ...
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0answers
35 views

why doesn't EM waves get weaker as we travel further away from the source [duplicate]

I know that as we get further away from the charge or from the magnetic field source both magnetic field and electric field decreases ,so why don't electromagnetic waves get weaker as the travel ...
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1answer
24 views

Electric Field & Polarization

Does everytime the electric-field $E$ & the electric displacement vector $D$ are parallel for every material?
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1answer
28 views

Does a field gain energy or does the mass/charge?

My textbook reads that when a mass/ charge is moved into the influence of a gravitational/ electric field the field gains/ loses energy rather than the mass/ charge. How can this be explained?