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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Contravariance and covariance of vectors

My main source of confusion is the following. Suppose I have a scalar potential $V(x,y,z)$. The electrostatic field for this potential is $ \vec{E} =\vec{\nabla}V = \frac{\partial{V}}{\partial{x}}\...
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Electric potential vs electromagnetic potential questions

We were all taught about the electric potential $V$, which is defined up to a constant, and can be measured with a voltmeter or an oscilloscope. On the other hand, in electromagnetism are defined the ...
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Contradiction from Poisson-Boltzmann equations - Gouy-Chapman model

Recently I have been investigating the problem of a neutral solutions (with equal number of anions and cations) interacting with an infinite surface $z=0$ with electrostatic potential $\phi(z=0)=\...
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Plate with positive potential and Gouy-Chapman model

I am thinking about the following mental experiment. Imagine I have an infinite flat plate at $z=0$ with electrostatic potential $\phi_0$, i.e., $\phi(z=0)=\phi_0$. Now I embedded this plate within an ...
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How should I use the complex permittivity of a material?

Here: $$\epsilon = \epsilon' + j *\epsilon''$$ I understand that the first part ($\epsilon'$) is the relative permittivity of a material, while the second part $\epsilon'' = \frac{\sigma}{\epsilon_0\...
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Is there such a thing as infinitesimal electric field?

I am interested in calculating some response properties, namely, susceptibility and polarizability. In principle, susceptibility should be the functional derivative of the electron density to a ...
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A question regarding electric field and charges inside a conductor

In this figure there is a positive point charge in the cavity and it creates an electric field, this polarises the charges in the conductor and the negative charges move towards the cavity where the ...
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Simulator for trajectories of charged particles in electric fields?

I am looking for a numerical simulation program which computes the trajectory of a charged particle moving in an electric field. The electric field should be numerically determined by determining a ...
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Working of a van de Graaff generator

Experiments show that when a charged conductor is placed in contact with the inside of a hollow conductor, all the charge on the charged conductor is transferred to the hollow conductor. In principal ...
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Electric field strength [closed]

I have got a problem to solve which is quite a way out of my understanding and was looking for help: A thin, horizontal, straight rod evenly charged throughout the whole length, which is 2a, is in a ...
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Is the induced electric field in a current changing solenoid actually that what we call magnetic vector potential field?

Induced electric field $E$ in a changing current (i.e. changing magnetic field $B$) solenoid image creditis: https://faculty.uml.edu//Andriy_Danylov/Teaching/documents/L18Ch33InducedEcovered.pdf I was ...
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Bio Savart Law and volume of sphere?

$\frac {4\pi r^3}{3} $ is the volume of a sphere and it appears in this equation. I understand the cross product is the area of a parallelogram, but am curious how this volume is involved in the ...
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Charges on conducting shell with a conducting sphere inside it

If I have a spherical capacitor which is composed of a conducting sphere surrounded by a conducting shell and the space between them is filled with a dielectric , I assumed that the charge on the ...
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What is the signal velocity in a very thin enameled magnet wire?

I was wondering if in the case of a very thin enameled (i.e. sub-millimeter thick wire insulation dielectric usually made from polyimide) magnet wire the generated electric field of a signal transient ...
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Superposition principle for the electric field

I had read somewhere that superposition principle is valid for linear functions, but the electric field is not a linear function, then why is the superposition principle valid for electric field?
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What causes the electric field in a Daniell Cell?

I would like to know what causes the e-field in a Daniell cell. From a chemistry point of view, I do understand that this is initiated by a redox reaction in which Gibbs free energy is decreased. The ...
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Why charges does not move through the conductor here if potential at both ends of wire is same?

Two conducting solid spheres are kept apart, one with charge Q1 and radius R1 and the other with charge Q2 and radius R2. Q1=5Q2 and R1=5R2 When these spheres are connected by a conducting wire, the ...
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Radio Wavefront and Photons?

I have some questions related to radio waves, photons and propagation , transmission and reception. It’s my understanding a radio wave is a changing electrical and magnetic field that travels through ...
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By what medium is information about electric field propagation communicated?

After watching the recent Veritasium video on electricity, I, like many other people was skeptical. I got a 75m length of copper wire, and an oscilloscope, and ran the experiment myself. My results ...
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The second uniqueness theorem in electrostatics

Does the second uniqueness theorem just say that if there is an electric field that satisfies Gauss's law for a surface surrounding each conductor + a surface of elnclosing all the conductor, it is ...
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Gauss' Law in differential form applied to charged sphere [closed]

I need to use the differential form of Gauss' Law $$\nabla · \vec E = \rho / \epsilon $$ applied to a charged sphere to obtain that the exterior field is given by $$\vec E = \frac{Q}{4 \pi \epsilon r^...
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A proton and an electron are placed in a uniform electric field successively. Do these two particles experience the same force? [closed]

A proton is placed in a uniform electric field and then released. Then an electron is placed at this same point and released. Do these two particles experience the same force? The same acceleration? ...
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How does parity work for the electric field and electric dipole and electric quadrapole transitions?

It is known that the electric field is a (polar) vector and is odd under parity. Likewise, when an atom undergoes a dipole transition its parity must flip because the dipole electric field acts like ...
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Physics of an electrostatic water pump, is it even possible?

I have been trying to figure out how to approach this problem. Imagine a cylindrical shell made of insulating material. The top surface has a hole in its center, with a pipe extending up. The bottom ...
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What, precisely, using mathematics, is meant by "electric field with only an $\hat{x}$ component"?

I am currently studying the textbook Microwave Engineering, fourth edition, by David Pozar. Chapter 1.4 THE WAVE EQUATION AND BASIC PLANE WAVE SOLUTIONS says the following: The Helmholtz Equation In ...
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Why is the electric field inside a conductor with charges laying on its surface zero? Is something wrong with my understanding of the concept?

We know that the electric field lines of a unit (point) charge is represented by drawing lines in all the directions radially outwards or inwards (depending on whether the charge is positive or ...
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Field and potential due to dipole

My TB gives the formulae for electric field and potential due to a dipole as: $$|E| = \dfrac{k p}{r^3} \sqrt{1+ 3\cos^2θ}$$ $$|V| = \dfrac{k p}{r^2} \cosθ$$ Why are these expressions are not ...
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Does charge always reside at the edge of a conductor's surface

Say I have a circular metal sheet with a charge $Q$ on it do the field lines come out from the edges alone or from across the entire sheet?
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A question regarding electric field due to finite and infinite line charges

Consider I have a finite line of charge.If I find the electric field at a point near the centre of the line charge the net field is horizontal as the vertical component get cancelled.If I find the ...
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Fault/Technicalities with poynting theorem

When finding the force on a system of point particles $Q_{1}, Q_{2}$, we need to use the formula $$\vec{F} = Q_{1} \vec{E_{2}}$$ Where $\vec{E}_{2}$ is the field ONLY due to the charge $Q_{2}$, since ...
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DC Bias Characteristic of Ceramic Capacitors under Transient

It's pretty well documented that many ceramic capacitors will "shed" capacitance with increasing DC bias. Seems that the mechanism is pretty well outlined too. (The physics behind DC voltage ...
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Electric field lines intersection with common tangent [duplicate]

We say that electric field lines do not intersect, because that cannot be two directions of electric field. Then can electric field line intersect in the way shown below? This image shows that two ...
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1 vote
1 answer
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Flux through faces of cube if charge is placed at an edge-center

The charge at edgecenter will be shared by 4 cubes so each cube will get $q/4\epsilon$ . The adjacent faces of the edge ( where the charge is located ) will have $0$ flux through them as no Electric-...
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Does a change in electric field cause a change in magnetic field, or do both just always happen together?

I'm taking an entry-level Physics class. From my understanding, a change in electric field does not "cause" a change in magnetic field, but rather, both just always happen together out of ...
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Voltage and electric field in a closed circuit confusion

I have a doubt about the intuition behind Electric field and Potential difference. Let's imagine a closed circuit with a battery, a resistance and a lightbulb. We observe that the lightbulb is on. ...
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How to calculate Electric and Magnetic Field of TEM waves through a coaxial cable?

So basically if you have a coaxial cable (inner radius a and outer radius b) with a dielectric between the two conductors (with permittivity ϵ and magnetic permeability µ ) and the monochromatic TEM ...
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Why do we consider external electric field in Gaussian equation of electric flux?

We know in the Gaussian equation that the net flux through a closed surface is equal to the flux of the charge inside the surface. Mathematically we see that the left hand integral consists of the ...
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What is the meaning of a conductor in equilibrium?

Electric field lines are always perpendicular to the surface of a conductor in equilibrium. what is the meaning of a conductor in equilibrium?
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Will a surface perpendicular to the electric field always be equipotential

In the figure attached there are four different electric field vectors with different magnitudes, point away from A. My question is will C be an equipotential surface? i.e. will the potential ...
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Distribution of Charges on a Conducting Cup

A multiple-choice problem goes as follows: A small positively charged sphere is lowered by a nonconducting thread into a grounded metal cup without touching the inside surface of the cup, as shown ...
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2 votes
1 answer
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Gauss' law in the presence of surface charges [duplicate]

Assume $V$ is a volume such that $\rho=0$ in $V$ where $\rho$ is the charge density. Assume further that we have a surface charge density $\sigma$ on the surface $S$ enclosing $V$ such that the total ...
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For the interface between two linear, isotropic, homogeneous dielectric materials with no free charge, does $E$ remain continuous?

The title basically says it all. Does the normal component of the electric field stay continuous across the interface of the two dielectrics? My intuition is that it would not stay the same as there ...
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Is this formula for a hollow sphere or a solid sphere?

In the above image, my book has given a formula for calculating the electric potential of a sphere: $$\fbox{$V=\frac{Q}{C}$}\tag{1}$$ Here, $C=\frac{r}{k}$. Is $(1)$ a formula for a hollow sphere or a ...
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AP Physics: Continuity of electric potential for an infinite sheet

For the mcq question above, the answer key states that the potential is continous and the electric field is discontinuous. I understand how the electric field is discontinuous as it points in 1 ...
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How should the singularity of the Coulomb's law be understood? [duplicate]

The electric field at the point $\vec r$ due to a point charge $q$ at the origin $$\vec E=\frac{q}{4\pi\epsilon_0}\frac{1}{r^2}\hat{r}$$ blows up at the origin. In other words, the force between two ...
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What does it mean when we say that an object is neutral?

I am studying electricity and until about now I never really gave much thought to the statement that equal number of proton and electron means neutral charge. Like if we simplify the question and ...
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Does electric current flow from higher potential to lower potential or from higher potential energy to lower potential energy?

Here, $O$ is a field charge with a $+T$ charge. $A$ and $B$ are test charges with $+T_1$ and $+T_2$ charge, and they are fixed in place. Suppose the points at which $A$ and $B$ are situated are $P_1$ ...
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Capacitance of caapcitor with complex dielectric material

How do I find capacitance of capacitor if we insert a material in capacitor that has a dielectric constant which depends on position inside a capacitor? For example two plates of capacitor filled with ...
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Why is it not possible to calculate the distance of a sensing electrode to a grounded object based on the measured capacitance?

Hello I am currently working on a scientific fair project where I want to measure the capacity between a sensor plate and a moving grounded object and thus calculate the distance between them. So far ...
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What is the electric field and potential inside and outside grounded conducting and non grounded conducting sphere?

I'm taking an electromagnetic theory course, but I have trouble understanding the field and potential inside and outside of a conductive sphere when it is connected and not connected to ground. And ...
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