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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28 views

Current flow because of a point source

Do I understand this sketch correctly, that the technical direction of flow is drawn here? In case of a cathodic pulse from the point source, the physical direction of the current would point away ...
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45 views

How to know there is zero polarization using electric displacement?

A sphere of radius $R$ carries a polarization $$\mathbf P(\mathbf r)=k\mathbf r$$ where $k$ is a constant and $r$ is the vector from the center. (a) Calculate the bound charges $\sigma_b$ and $\rho_b$....
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84 views

Is electric potential gradient a scalar or vector quantity?

It's an image from my textbook where it's written that EPG is scalar but at some sites I read that it is vector.
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34 views

Charge of capacitor

Consider a slab of dielectric material sandwiched between the metallic plates of a capacitor. Call $l$ the thickness of the slab and $A$ its surface area parallel to the plates. Can you explain me why ...
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4answers
82 views

Is the field used in the Gauss Law affected by the outer charge configuration?

Following is the Gauss Law: $$\oint E\cdot\mathrm dA = \frac {q_\text{enc}}{\epsilon_0}$$ Now consider the following scenario: The electric field in the following case, at the sphere, is due to $q_1+...
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3answers
131 views

How does a copper wire encase electric field lines inside it while conducting current?

When we connect the positive and negative terminals of a cell with a copper wire, the electric field lines travel through the wire. What is it about the copper wire that it is able to encase almost ...
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2answers
62 views

Field lines of two charges whose algebraic sum is not zero

I know that field lines are directly proportional to the value of electric charge. Assuming that $8$ lines of force, or of field, of the come out of the charge $+q$, then $16$ lines of force will come ...
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2answers
150 views

What makes electrons in the conduction band conductive?

We say electrons must jump from the valence band to conduction band in order to be conductive. Why is that the case and why can't electrons in the valence bands themselves be conductive? Is it because ...
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1answer
19 views

Closed surface present in a electric field, no charge inside then net flux is zero. So what does that tell?

It means like water entering and whole water coming out so net flux is zero, I know that but so what? Isn't that obvious? and even if it is not what does that tell about electric field and it's ...
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Can Vera Rubin's findings be explained by a distribution of charge?

Vera Rubin found that the rotational velocity of galaxies is much greater than expected at greater distances from the center. Gravity from an invisible mass is assumed to account for this measurement. ...
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1answer
32 views

Electrostatic boundary conditions notation

In one book example we are trying to find the electric potential of a infinite long steel bar that is homogeneously charged that has a radius $R$. And We will be using the discontinuity of the normal ...
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62 views

Is there a fix amount of energy stored in magnetic fields?

$B= (\mu/4× \pi) × q v (\sin\theta/r^2)$ $ \mu = \text{ permeability of medium}$ $q = \text{charge of the object} $ $r = \text{distance object}$ $v = \text{ the velocity of object}$ $\theta$ = angle ...
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Why is linear charge density used for field of conducting cylinder? [duplicate]

here is a page from hyperphysics explaining conducting cylinder electric field. Why do they use linear charge density
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102 views

Electric current and potential difference

I have lots of doubts regarding electrical energy, electric current and voltage. I have tried to understand as much I can but every time I try to completely clear my concept, I encounter a dilemma! So ...
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1answer
75 views

Question about cancellation of electric field

Why can't I cancel the two opposite electric field shown below? I already searched about this and saw the article that says "It can't cancel each other because they aren't in the same region.&...
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2answers
104 views

Sustaining a current in conductor placed in external electric field

Consider the following arrangement- We have a conducting sphere and a positively charged infinite sheet on the left. The field creates induced charges and the net electric field inside the conductor ...
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3answers
61 views

Can anyone show me how the definite integral is derived in the solution? [closed]

This example is from 4th edition, David J. Griffiths. I don't understand how the definite integral is calculated. Can anyone show me?
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110 views

What produces the electromagnetic fields in the light wave when photons are chargeless?

If there’s an electromagnetic field in the propagating light wave there must be an electric charge producing it, but photons are charge less, so how are these electric and magnetic fields produced and ...
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2answers
101 views

Why is the quantum operator for a photodetector $\hat{E}^{(+)} \hat{E}^{(-)}$ and not just $|\hat{E}|^2$?

According to this resource, the quantum operator for a photodetector is $\hat{E}^{(+)} \hat{E}^{(-)}$. In classical physics a photodetector measures the square of the electric field: $|\hat{E}|^2$. So ...
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1answer
19 views

Electric potential for positively charged central object anf negatively charged central object

How are the values of electric potential for negatively and positively charged central particle evaluated? Is potential at a distance $d$ from negatively charged central object more than that of ...
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2answers
99 views

Can you electrically polarize gas?

If you put a non-polar gas like $\rm CO_2$ in a positive electric field, Will it get polarized? What will be the force the molecules get as its attracted to the positive field?
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47 views

Unequal arm length Michelson Interferometer Light Intensity

Imagine a Michelson interferometer with unequal arm length. A laser beam with an electric field of the form $$E(t,z) = 2E\cos(ωt+kz)$$ is incident on a 50/50 beam-splitter. The first arm is of length <...
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1answer
58 views

Calculating the Dipole moment of an insulator in an electric field

I know that the dipole moment equation is $p = qd$, but when I looked at videos and articles, they only talked about polar molecules. If I put an insulator for example co2 in an electric field, what ...
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1answer
39 views

How powerful does an electric field have to be to attract carbon dioxide?

I was reading about a Van de Graaff generator and I was curious to know if it can attract air. Specifically, if an electric field is powerful enough, can it attract carbon dioxide?
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3answers
59 views

Line integral of electric field in a metal cavity

Suppose there's a conductor with a cavity in which we introduce a positive charge $Q$ now the charge shall induce $-Q$ on the inner walls of the cavity so that By gauss law the net field in conductor ...
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1answer
78 views

Is the divergence of electric field in a solid cube of uniform charge density position dependent?

Within a solid, uniformly charged non-conducting cube, the electric field is clearly position dependent, does that make the divergence of the electric field position dependent as well? If that is the ...
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21 views

Discontinuity of potential due to point charge at dielectric boundary

Suppose we have point charge $q$ enclosed in a uniform spherical dielectric medium of dielectric constant $\epsilon$ with radius $R$. The electric field due to that would be: $$ \vec{E}(r) = \begin{...
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1answer
18 views

Is the $E$ field near a thin cylindrical line charge stronger than a thick one at the same voltage?

Compare two infinite cylindrical conductors held at the same voltage $V$, with diameters $R_1$ and $R_2$. The electric field strength and voltage outside the conductor are $$ E = \frac{\lambda}{2\pi\...
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1answer
33 views

Is there a mathematical limit to the summation of infinitesimal magnetic and electric field in the Lorentz Force?

The addition of infinitesimally small parallel electric and magnetc fields, irrespective of their origin or source, or physical feasibilty; seems to produce a seemingly impossibly large force. Or at ...
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1answer
31 views

How does an external electric field induce a symmetry lowering perturbation to the $D_{3h}$ point group?

I have the following homework style question which I will typeset 'word for word'. I am having trouble understanding the authors' solution to part $\mathrm{ii}.$ of the following questions: An ...
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5answers
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Where does the energy stored in inductor go on opening the switch?

Suppose we have a simple RL circuit. At $t=0$, I close the switch so that current starts flowing in the circuit. When the steady state is achieved, current $i=\frac{\epsilon}{R}$ would be flowing in ...
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3answers
87 views

Why does Gauss' Law apply to any shape given that it's a closed surface?

I've read some answers on stack exchange for this question, but I don't find them particularly clear. I am convinced of the case for a sphere, since the area of a sphere is used in the derivation for ...
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1answer
32 views

Why does the charge distribution on the surface of a conducting sphere remain uniform even if there is a perturbation in the inner electric field?

In a conducting sphere, the net charge is evenly distributed at the surface because of repulsion while the inner electric field remains zero as charges cancel inside. Here is an example, where the net ...
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16 views

How does field effect work on graphene?

I am trying to understand how the field effect from a gate works on graphene. Does the gate voltage affect the bands or the Fermi level? When studying how gate voltage affects a semiconductor, I ...
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1answer
44 views

Equation of infinitesimal ring when finding $ \vec{E}$ of a disc?

When trying to find the electric field created by a uniformly charged disc at a point P on axis of the disc, it can be done by integration. We start by finding the electric field dE created by each ...
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1answer
23 views

Does the addition of a static charge or magnetic field to an antenna affect the EM waves it's supposed to receive?

I read this: Does laser beam (EM wave) affect magnet next to it? But I distinctly remember the use of a magnetic field to alter the polarization of light. Doc Edgerton used this technique to create a ...
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1answer
41 views

Can you use center of charge to find electric field of a not-centered point near a uniformly charged rod?

Suppose we have a uniformly-charged rod has charge density $+\lambda$, and we want to know the magnitude of the components of electric field at point $P$. The standard method of solving for the ...
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34 views

What would happen if very strong electric field is applied to the surface of conductors?

I know that if the conductor is at the negative end, it can emit electrons (field emission) when the electric field is sufficiently strong. But what if the conductor is at the positive end? Will the ...
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3answers
413 views

Trajectory of electric field lines

I came across an interesting problem of electric field which is as follows: An electric field line from a charge $q$ is as shown. It enters a negative charge $–q$ as shown. Find the maximum height of ...
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29 views

Influence of the current polarity in the Hodgkin-Huxley model

Suppose I place a monopolar electrode at a certain distance from a target neuron, which can be described by an electrical circuit according to the HH model (see picture). Why is there such a ...
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3answers
84 views

Mathematical Ambiguity in Electric field at centre of a uniformly charged hollow hemisphere

So there is a question in the book "Problems in General Physics" by IE Irodov to calculate the electric field at the centre of the hollow hemisphere. I was able to solve this question and ...
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1answer
39 views

Electric flux through a infinite strip

We have to find flux due to a point charge at $(0,l,0)$ on an infinite strip lying in region $(0,0,0)$, $(l,0,l)$ and extending to infinity along $+x$ direction. I am aware that a general case has ...
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1answer
62 views

Recipe for finding non-conservative electric field in general case

I know that Faraday's law gives a recipe for finding the EMF over a closed loop. But, other than through symmetry arguments, I have not found a way discussed in my textbooks on how to find explicit ...
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1answer
51 views

Potential difference due to point charges

Now, there are many sources saying the potential difference created by a point source is given by \begin{equation} V=\dfrac{1}{4\pi\varepsilon_0}\dfrac{Q}{r} \end{equation} Which looks like it's just ...
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27 views

Are there any magnetic field while electron transfer in static electricity

I already know that the moving charge can generate magnetic field. But in this case, can magnetic field be generated. Thank for answers PS. This is just my curiosity.
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1answer
38 views

How strong an electric field is needed to violate electrostatic equilibrium of usual conductor?

As is told by almost all textbooks, a conductor reach electrostatic equilibrium in an elctric field. My quetion is that, is there any kind of conductor, which has so few electrons and eletron-like ...
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4answers
232 views

Using symmetry in Gauss' Law

I have to find electric field at any inside point due to a uniformly charged solid sphere I do it in following steps $\to$ First I choose a spherical gaussian surface passing through required point ...
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3answers
43 views

Definition Of Electric Flux

I have some confusion in definition of electric flux . I have been told that No. of electric field lines passing through a surface area gives/represents electric flux but if suppose $n$ number of ...
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1answer
43 views

What does the Polarisation Vector signify?

...The electric field produced by the $i$-th laser is described by $$\vec{E_i}=E_{0,i}\vec{ε_i}\cos(\vec{k_i}\cdot\vec{r}-\omega t)$$ with the amplitude $E_{0,i}$, the wave vector $\vec{k_i}$ and the ...
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2answers
36 views

Electric field outside of a conductor with charge $q$

Suppose that I have a spherical conductor (radius $R$) with a cavity at the center and a charge $q$ inside it. I know that the electric field outside of the conductor will be $$\vec{E}=\frac{q}{4\pi\...

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