# 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 ...
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 ...
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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### 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 ...
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 ...
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 ...
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 ...
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 ...
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 ...
35 views

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### 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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### 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 ...
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 ...
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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### 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 ...
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 ...
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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### 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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### 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 ...
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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### 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 ...
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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### 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, ...
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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### 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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### 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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### 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 ...
### 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 ...