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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.

2
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2answers
43 views

Can I write a 2-dimensional electric field as an analytic function on the complex plane?

Let's consider a two-dimensional electric field $\textbf{E}=\textbf{E}(\mathbf x)$, where $\mathbf x\in \mathbb R^2$, and $\textbf{E}$ is a vector representing the direction and strength of the field ...
0
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2answers
25 views

Is it necessary that the potential difference between any two equipotential surfaces in a system be constant?

Is keeping $dV$ constant a necessary condition in the formula $$E=-\frac{dV}{dr}$$ for equipotential surfaces ?
0
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0answers
41 views

What is electric field on the surface of a surface charge?

Electric field just near the surface of a surface charge is $\dfrac{\sigma}{2 \epsilon_0} (\hat{n})$ on one side and $-\dfrac{\sigma}{2 \epsilon_0} (\hat{n})$ on the other side. What would be the ...
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0answers
31 views

Dipole Inside Cavity of A Spherical Conductor

Consider the following case: There is a short electric dipole placed arbitrarily inside a spherical cavity inside a solid,uncharged conducting sphere We need to find electric field at a point ...
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3answers
44 views

If an electric field passing through a dielectric medium, back into the original medium, is it “back to normal”?

Suppose there is an electric point charge causing an electric field E in a medium with a dielectric constant $\epsilon_1$. You can calculate the scalar potential $\phi$ at a given distance $r$, as ...
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1answer
42 views

Electric Field for two identical charges [on hold]

I have a task to find an electric field I don´t know how it should look like: We have 2 identical charges $q$ at a distance $d$, on x-axis at $(\frac{d}{2},0,0)$ and $(\frac{-d}{2},0,0)$. How can I ...
2
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1answer
83 views

How can direction of electric field due to a moving charge be from the present position of charge?

According to Maxwell's Equations, the electromagnetic waves in vacuum travel at the speed of light $c$. While solving Maxwell's equations using Lorenz gauge conditions (or basically evaluating scalar ...
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3answers
45 views

Current density and electric current [on hold]

Suppose we have a wire, having different cross sectional area at different points. We know that for same wire we have constant Current density at every point of wire. Thus we can say that if at ...
0
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2answers
45 views

Why Electric field inside the spherical shell is zero? [duplicate]

electric field in and out of the spherical shell Why the field inside the conducting spherical shell is zero? Professor Lewin said and I quote," there is NO charge inside the conductor because any ...
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0answers
14 views

Electric field of a line of Charge on it axis using electric potential

We have a line of charge with length $L$ and charge density $\lambda$ and we want to find its Electric field on a point $p$ with distance $d$ from one end of it using potential. I drew a picture like ...
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0answers
10 views

How to calculate Average Electric Field for a microscopic filed in dielectric?

In Griffith's book in The chapter of Electric Fields in Matter (The field inside dielectric) , He has considered the Sphere of Radius R and for the inner dielectric element He used the field as $$\...
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2answers
27 views

Why do 2 charged conductors gain same potential when connected via wire

Why do 2 charged conductors gain same potential when they are connected via a wire.Can somebody also give a mathematical proof of it?
1
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1answer
48 views

How do resistors form electric fields and thus potential drops?

$$V_{ab}=-\int_b^a\vec{E}*\vec{dl}=\int_a^b\vec{E}*\vec{dl}$$ By Kirchhoff's loop rule, the sum of the potential drops across a closed loop is zero. Going in the direction of conventional current ...
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0answers
90 views

Static electric field which admits no potential

Conservative condition for (static) electric field $\mathcal{E}$ is usually defined as $\mathcal{E}$ being closed (curl-free). Now this clearly holds when for the given manifold $X$ we have $H_\text{...
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1answer
19 views

Casimir Force and Electric Field?

I found the wiki article a bit misleading because I took $<\mathbf{E}>$ as an electric field... the equation in question is $$\frac{F}{A} = -\frac{d}{da} \frac{<\mathbf{E}>}{A} = - \frac{\...
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1answer
55 views

Lorentz transformations: Distance vs “retarded distance”

Suppose I have a charge situated at rest in one inertial coordinate system. The field of that drops inversely with the square of the distance. If I perform a Lorentz boost where $$v^2« c^2$$ (not ...
2
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2answers
54 views
+50

Electrostatic values where there are some charge

I've started asking myself: What is the value of the electric field at the surface of a shell with uniform distribution? In particular, is it infinite, as this point is over an (infinitesimal) ...
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0answers
11 views

Get electric field magnitude from equipotential graph

How would I calculate the magnitude of the electric field at a given point? I know that $E_x={-{dV}\over{dx}}$, and that $\Delta{V=-}\int{E}\cdot{dr}$. However, I do not know how to get the ...
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0answers
7 views

How to Measure Electric-Field Probe Sensitivity?

I am doing some reading on current methods for detecting electric fields. A figure of merit for the systems is, naturally, the minimum strength of field that can be measured, in units of Volts per ...
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0answers
20 views

Electric field in a circuit static vs induced

I am on a quest to learn Maxwell's equations and feel I have made a lot of progress in understanding of them. But there is one thing that is bothering me. In a static electric circuit, the electric ...
0
votes
1answer
24 views

Is there an electric field in a poled piezoelectric crystal at rest?

From my understanding, after a piezoelectric crystal is poled, all the dipoles are roughly aligned inside it, so that the piezoelectric effect is not negligible. However, wouldn't that result in a ...
1
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1answer
26 views

What is the electric field due to a charge inside a hollow sphere? [on hold]

Say, there's a hollow non-conducting sphere with no charge. If a point charge q is placed inside the sphere, how will the electric field behave? Now inside the sphere I can just apply Gauss's law. ...
0
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1answer
31 views

Convert graph of voltage to electric field lines

I have a physics lab which involved connecting wires to two points on a conductive paper and supplying a voltage. We measured the voltage at every point on the paper and made a graph of the results. ...
4
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2answers
30 views

Derivation of $B$ field and $E$ field

For an infinite plate of charge, the E field is (density of charge per area) divided by (2*vacuum permittivity). In deriving it, we used Gauss' Law and say that the flux through the two ends of the ...
0
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1answer
38 views

Is the electric field from light independent from the light magnetic field?

I was reading about antennas and I found an statement somewhat like this "loop antennas are more efficient compared to other antennas when close to the human body since the human body interacts more ...
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0answers
29 views

Find electric field for a hemispherical shell using Gauss law [closed]

The hemispherical shell has charge density $σ$ find electric field at its centre I know how to do it by integration but I tried to do it using Gauss law and answer I got was correct but I am not sure ...
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votes
1answer
80 views

An $E$ field with no $B$ field in a region?

Assume there exists a time-varying current source ${\bf J}({\bf r},t)$ in otherwise vacuum and a region $R$ that does not intersect the region of support for ${\bf J}({\bf r},t)$ (That is ${\bf J}({\...
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2answers
48 views

Why is there no negative sign in the formula of work against electric field?

Why is there no negative sign in the first formula of work done against electric field where as second formula below has it?
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0answers
34 views

Electric flux through y-z plane in a dipole [closed]

A dipole lies on the $x$-axis with positive charge $+q$ at $x=d/2$ and the negative charge $-q$ at $x=-d/2$.find the electric flux $Φ$ through y-z plane placed midway between between the charges. My ...
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0answers
18 views

Proving continuity of potentials and fields due to a surface charge

Is there a way to show: $(1)\ \displaystyle \phi=\int_{S'} \dfrac{\sigma}{r} dS'$ is continuous all over space $(2)\ \mathbf{E}=\displaystyle\int_{S'} \dfrac{\sigma}{r^2}\ \hat{\mathbf{r}}\ dS'$ is ...
0
votes
2answers
23 views

Calculating electric field in cylindrical symmetry- - Trying to understand electric field/potential in 3D with cylindrical coordinates

Trying to work through this question I am sure that I am doing something wrong. We start with a uniform electric field $$ E = E_o \hat{i} $$ and then find that the potential is given by $$ V=-E_0 ...
0
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3answers
66 views

Why the electric potential inside a conductor doesn't equal zero?

Assume that a negative charge in the space near of it a small positive charge, Then for sure that the negative charge will attract the positive charge naturally because it has an electric field around ...
2
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0answers
29 views

Integrand discontinuity of surface integral of electric field of dielectrics

I am reading an article here on dielectrics Equation $(4.10)$ is: $$\Phi(\mathbf{r})=\dfrac{1}{4\pi \epsilon_0}\int_{V} \dfrac{d^3r'}{|\mathbf{r}-\mathbf{r'}|} [\rho (\mathbf{r'})\ -\nabla'.\mathbf{...
1
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2answers
68 views

What is the electric flux through the flat and curved surfaces? [closed]

My question is from Physics For Scientists And Engineers 7th: A particle with charge Q is located immediately above the center of the flat face of a hemisphere of radius R, as shown in the figure. ...
0
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2answers
36 views

Current law explained

Kirchhoff's Current Law (KCL) is experimentally proven but what exactly happens?. I have made a model by taking the drude model and adding the interactions between the electrons and the reason why ...
0
votes
1answer
31 views

approximation to the dipole of 2 infinite line charges

This is the question: 2 infinite line charges are located at distance $l$ and charged with linear charge density $\lambda $ and $-\lambda$. Find the electric field and the electric potential away ...
1
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2answers
57 views

Why the electric field of an infinity line is dependent on distance? [duplicate]

A very common question about Gauss law is being asked in schools or Internet: Why the electric field of an infinite plane is independent on distance? Actually I was one of who asked this ...
0
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2answers
49 views

Electric field inside a cavity

What is the electric field in the cavity, if the conductor having the cavity is charged? Does the result depend on the shape and size of the cavity or conductor? Ans given in my book is Zero and No ...
1
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1answer
24 views

Query about the electric field of a uniformly charged rod at the ends of the rod

I found the electric field of a uniformly charged thin rod to be, $E=\frac{Q}{4\pi \epsilon_0 (a^2-x^2)}$. Where $L_{rod}=2a$ and $x$ is the distance away from the centre of the rod, along the its ...
2
votes
1answer
56 views

If electricity creates a magnetic field, could a (strong) magnetic field stop electricity? [closed]

Surely this would make the two magnetic fields interact and if movement was made impossible, the stronger magnetic field would block the weaker electromagnetic filed. Am I right (presuming that the ...
-3
votes
0answers
41 views

Please tell me I finally understand Gauss's Law (flustered for a couple days)

For the past few days I've been confused over using Gauss's Law to find the electric field of an infinite conducting sheet of charge. I believe I have figured out why my reasoning below is wrong, so ...
1
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1answer
34 views

Induced Electric Fields and Faraday's Law

I'm an undergraduate student and we just covered Faraday's law. However, I am still confused conceptually about a few things: Faraday's law states that $\oint_{\partial\Sigma} \vec{E} \cdot \vec{dl} =...
0
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0answers
42 views

Is this a valid explanation for why charges in a conductor move to the outer surface?

This is a drawing of a spherical conductor with a hollow center. The black dots represent +ive charges, and the arrows represent their electric fields. I am assuming the black dots start on the inner ...
0
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4answers
88 views

Are electromagnetic waves a substance? [duplicate]

I would generally consider fields to not be substances, since substances are generally associated with matter. I know that energy is not a substance. Are electromagnetic waves a substance?
0
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2answers
41 views

Work done against an electric field

When moving a charge against an electric field, we need a force or acceleration to overcome the constant force of the electric field.if the force applied is equal to the force of the electric field ...
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0answers
35 views

what is the relation between electric conductivity and permittivity in the steady state?

I find good answers like http://pleclair.ua.edu/impedance/The%20Relationship%20Between%20Loss.pdf for the case that there is a omega!=0 (equation 11), but what about the trivial (?) steady state? ...
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0answers
41 views

Electroshielding in asymmetric conductors

Consider the textbook problem of a spherical conductor, with a concentric spherical cavity and a charge of +Q located in the center. By constructing a suitable Gaussian surface, we can deduce that the ...
3
votes
1answer
60 views

Electric potential and field due to a continuous charge distribution

(1) The electric potential due to a continuous charge distribution is: $$\psi=\int_V \dfrac{\rho}{r}\ dV$$ To calculate this integral $\rho$ must be continuous over $V$. But $\rho$ is discontinuous ...
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1answer
39 views

Helical motion of a charge in magnetic and electric field

Suppose there is a positive charge undergoing circular motion in the x-y plane because of a magnetic field acting in the negative z direction. If a uniform electric field is switched on in the same ...
10
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5answers
2k views

How can I prove that a state of equilibrium is unstable?

In the particular problem I encountered, an electric field was zero at the origin and we were meant to prove that a particle at the origin was in an unstable state of equilibrium. Is it enough to ...