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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20 views

Can the signs of charge of electron and proton be reversed?

I was thinking that the electron, proton, neutron etc. are human given names to some particles. So, are the signs, positive of proton and negative of electron, given just to show their opposite ...
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1answer
32 views

Charge Distribution on a Strip

let's consider a microstrip line connected to a voltage source V0 (applied between the strip and GND plane). According to foundation for microwave engineering (collin) book, the surface charge density ...
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1answer
563 views

Determining electric displacement using Gauss's law

This is an example problem from my E&M textbook that I don't quite understand: A metal sphere of radius a carries a charge $Q$. It is surrounded, out to radius b, by linear dielectric material ...
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1answer
33 views

What is the term for neutral electric field density?

What is the word or way of referring to a neutral electrical potential. For example let's say you have a 10 cm sphere of electrically neutral mass that is 1 Kg mass and you separately have a different ...
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3answers
420 views

Using Gauss's law to prove that a field is zero

I have seen countless examples where Gauss' law is applied to state that the electric field in a region is zero. For example, taking any Gaussian surface inside a spherically conducting shell where ...
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1answer
36 views

How would field lines look if we put a ring inside an electic field?

We have a container with two electrodes and this container is filled with a thin layer of not distilled water. Field lines will be something like this, I believe: But how would field lines look like ...
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1answer
632 views

How do insulators lose their charge?

Some theoretical questions that got me confused during physics lecture today. bringing a conducting balloon to a negatively charged rod close will allow the conducting balloon have positive charges ...
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1answer
43 views

A typical question of electric field [closed]

Two wires AB & CD, each of length 1m, carry a total charge of 0.2 microcoulomb each and are placed as shown in figure. The ends B & C are separated 1 m distance. Determine the value of ...
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2answers
47 views

About the electric field inside a capacitor

If I have a metal sphere (a conductor) of radius $R$, carrying charge $Q_1$ with potential $V_1$, surrounded by a thick concentric metal shell (a conductor with inner radius $a$, outer radius $b$, as ...
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2answers
35 views

Is the E field generally conservative outside the cases when vector potential goes to zero?

In Ronald Wangsness' "Electromagnetic Fields" book, he states that $\textbf{E}$ generally depends on both a scalar and vector potential in the form, $$\textbf{E} = -{\bf \nabla}\Phi -\frac{\partial \...
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2answers
154 views

Is this the correct voltage graph of a conducting sphere in the presence of another charge?

This grading rubric show an example of an acceptable answer, however I wonder if the slopes at the surface of the second sphere are wrong. This is a previous AP Physics test question so I'm inclined ...
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2answers
163 views

Gauss' law for two point charges and a factor of $4\pi$

When we model electric field as something that represents the "flow" of something that is conserved, we can prove that the flux due to a single point charge, through the following surface, Flux ...
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3answers
316 views

Field Theory: Electric Field

I am a grade 12 student, and we are learning electric flux. We covered electrostatic forces and, now we are on electric flux. We defined electric flux as the total number of lines of force passing ...
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2answers
989 views

Charging capacity and capacitance of a conductor

I know that charging capacity of a conductor is the maximum charge a conductor can hold And capacitance is the ability of a conductor to hold charge in a given potential . But how are these two ...
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5answers
129 views

Paradox in Circuit Theory

Consider the simple case of a battery in series with a resistor, mediated by conducting wire. At steady state, the charge carriers are circulating around the circuit at constant speed through the ...
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1answer
764 views

Principle of capacitor

It is said that second conductor reduces the potential of fist conductor and hence increases charge taking ability of first conductor My confusion... As per my limited knowledge it is electric field ...
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1answer
140 views

Fully filled capacitors with parallel dielectrics problem

consider that we have two dielectrics inside a capacitor as shown in the picture, let0s consider also that Q is the charge of the capacitor and d the distance between the two plates , the first ...
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24 views

Force on charge next to dielectric half space

Given the charge q placed at (0,0,d), next to an infinite half space filled with a dielectric with $\epsilon_1$ which extends to z<0. Calculate the Force on the Charge by Integrating the stress ...
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35 views

Electrostatic field flow generated by two spheres

I was doing homework and I finished an exercise in which I think I have done something wrong, I would like to discuss it with you. The statement is as follows (translated from spanish, I'll reply to ...
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2answers
76 views

Faraday's criterion (The magnitude of Electric field is proportional to the number of field lines)

According to Halliday et al, the magnitude of Electric field is proportional to the number of lines per unit area perpendicular to the field. My book (Halliday et al) states that this criterion, ...
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2answers
684 views

Why is the divergence of the field zero in Maxwell's equations?

I read in a book called Vector Analysis by Murray R. Spiegel by Schaums Series, and I found that there is somewhere printed that the divergence of the electric field is zero. Since my teacher told ...
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2answers
29 views

Magnetic and Electric Field Lines between Conductors

let's consider a system made with 3 conductors: two parallel wires (in this case rectangular wires) and a plane (GND) below them. Consider the following situation in which both wires are connected to ...
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2answers
40 views

How to draw quiver plot for complex-valued electric field?

I have a matrix of complex numbers for the electric field inside a medium. Since I want to draw the quiver plot of these elements, it will be completely different if I only use the absolute part. Then ...
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1answer
503 views

Finding the maximum value of electric field for a given two-dimensional charge distribution

Suppose you have a surface of finite area with a fixed surface charge distribution. Does a maximum electric field magnitude $|\vec{E}|_{max}$ exist for each and every possible surface area? If yes, ...
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1answer
132 views

Does electric and magnetic field interact?

Can electric field or magnetic field interact with an Electromagnetic radiation? And can 2 electromagnetic radiations interact with each other? Rather than the interference effect.
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1answer
37 views

Energy of a dipole?

Suppose that we have a perfect dipole with $+q$ at $\vec{r}+\vec{d}$ and -q at $\vec{r}$, and that this dipole is in a uniform electric field $\vec{E}$, Then: \begin{equation}U=-\vec{p}\cdot \vec{E}....
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28 views

Electrostatic potential of a charge distribution with a uniform electric field

I'm trying to solve an exercise in which I have certain charge a dielectric distribution that is useful to solve in spherical coordinates. In particular, it's a spherical dielectric of radius $a$ ...
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1answer
43 views

Capacitor problem: What's wrong with this?

The capacitor shown contains 3 different dielectric material $\epsilon_1,\epsilon_2,\epsilon_3$ between the top and bottom metallic plates on which lie teh points $A$ and $B$ as shown. The electric ...
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1answer
22 views

How to calculate the work done in moving a charge inside an eletric field between two oppositely charged plates?

As title says I'm having trouble trying to figure how to calculate the work done in moving the charge. This is an exercise from the book "Physics for Computer Science Students" chapter 14. I didn't ...
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6answers
5k views

What is the origin of the Dirac delta term in the dipole electric field?

I am a bit lost how one has deduced the formula for electric field with electric dipole because of some inconsistency between different sources. The Wikipedia article contains a delta function in the ...
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3answers
3k views

Is the electric field strength along an equipotential surface constant?

I'm trying to determine whether or not the electric field strength $|\vec{\mathcal{E}}|$ is constant everywhere on an equipotential surface. I know an equipotential surface is defined as $$ S = \{\...
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15 views

Dielectric Slab: Force due to fringing field

A parallel plate capacitor whose plates are maintained at a constant potential difference has a partially inserted dielectric slab. The force on the dielectric slab is given in most of the books. (...
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1answer
35 views

Calculating the electric field strength in parallell plate capacitor

Two parallell quadratic plates with side $\ell$, distance between $d$ and between the plates there is a material with relative permittivity $\varepsilon_r$ and conductivity $\sigma.$ By applying ...
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1answer
28 views

Why is there higher voltage drop across larger resistors?

By simple application of $V = IR$, there must be higher voltage drops across larger resistance. However, $V$ is the integral of $E$ multiplied by displacement. Thus, the electric field must be larger ...
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1answer
139 views

What happens with the divergence of maxwell stress tensor when EM fields in vacuum?

The conservation momentum can be derived from the total electromagnetic force on the charges in volume $V$ and is written in this way: $$ \frac{d\vec{p}_{mech}}{dt} + \frac{d}{dt} \int_V (\vec{E}\...
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3answers
47 views

How does a time varying magnetic field confined in a cylindrical region produces induced electric field even outside the cylindrical region?

We know from Faraday's Law of Electromagnetic Induction that due to Time Varying Magnetic Field (TVMF), a non conservative electric field will be induced. Now if we consider a cylindrical region in ...
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1answer
116 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 ...
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4answers
337 views

Divergence of $\frac{ \hat {\bf r}}{r^2}$ , what is the 'paradox'?

I just started in Griffith's Introduction to electrodynamics and I stumbled upon the divergence of $\frac{ \hat r}{r^2}$ , now from the book, Griffiths says: Now what is the paradox, exactly? ...
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2answers
35 views

What shape does the Induced Electric Field Lines take when in a region there is Non Cylindrical Time Varying Magnetic Field?

Everywhere in the literature I have across, I find that whenever the discussion of the Induced electric field comes, it is discussed around a cylindrical time-varying magnetic field. The induced ...
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1answer
22 views

Why do we represent symmetrical interactions between particles as two asymmetrical interactions?

For example, the interaction between two electrons: Both just symmetrically repel each other, but then we go on and describe this as two times the same asymmetric interaction: One particle generating ...
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2answers
306 views

Question about polarisation in dielectrics

I was going over my elecro statics course and in a textbook it gave an explanation on how molecules in a dielectric are polarised when placed in an external electric field. Diagram: They seem to be ...
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1answer
21 views

Is the surface of a Perfect Electric Conductor Equipotential in any Condition?

It is known that the surface of a PEC (Perfect Electric Conductor) is equipotential. This is true, in theory, in any situation (equilibrium or not), since the conductor is perfect and so the electric ...
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1answer
156 views

Electromagnetic wave equation with time varying phase velocity

I am attempting to solve Maxwell's equations for the electric field of an electromagnetic wave, with time varying phase velocity, propagating within a medium within unity permeability but time varying ...
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0answers
16 views

Finding Flux-linkage of incident field on square-loop antenna

I'm having a hard time grasping this problem. I have previously found and sketched a time-harmonic E and H field in a source-free area of a lossless medium, coming from a WLAN hub. I have an antenna, ...
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1answer
138 views

How to calculate the potential energy of an $H_2$ molecule

From left to right, electron $e_1$, $e_2$ and proton $p_1$, $p_2$. $r_0=0.529nm$ The total energy is sum of energy require to bring each particle to its place. Take the place of $e_1$ is zero ...
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2answers
36 views

Why is dipole potential independent of azimuthal angle?

In the formula for dipole potential in spherical coordinates, there is no dependence on azimuthal angle. I don't see why this is as by varying the azimuthal angle, i.e changing our position on the x y ...
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16 views

Can lead field be a scalar field?

In electrophysiology it is common to use lead (vector) field to describe relation between an electric dipole and a measured potential. Can the lead field be generalized as a tensor field? I am mostly ...
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3answers
23 views

Work done by the electric field on the charge - Negative or Positive?

Below is a question from my physics textbook: $X$ and $Y$ are two points in an electric field. The potentials at $X$ and $Y$ are $V_x$ and $V_y$ respectively where $V_x > V_y$. A small, positive ...
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2answers
82 views

Applying Ampere's law in situation with non-physical $E$-field?

On an exam I was given this question: Suppose an electric field in a region with no current $(\textbf{J}=\textbf{0}$) is given by $\textbf{E}(t,x,y,z) = \sin(\omega t)\hat{\textbf{k}}$ and $C$ is ...
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2answers
34 views

At what point in space do we measure the electric field of an electromagnetic wave?

In an electromagnetic wave, the electric field varies in magnitude and direction. This electric field is at some point in space, point in the direction perpendicular to its velocity. See the image ...