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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 ...

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Can two semi-infinite plane waves undergo perfectly constructive interference?

This is building off of a question I asked here. When discussing the linked problem with some friends, the consensus seemed to be that the reason two identical semi-infinite plane waves cannot ...
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1answer
23 views

Electric flux of a cube with charge at the center

I've known gauss' law that any closed surface with some net charge inside, the electric flux would be q/ε0 , but some professor told us that a cube cannot be a gaussian surface and that the electric ...
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D-Field between plates of capacitor and its relationship to B

I need a little help with the below question. I just quite see how everything relates together and how to solve the question. I guess I just don't understand the relationship between H and D and how ...
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Origin of electric flux and field lines [duplicate]

I wanted to know about the thoughtprocess which led to development of electric flux -Flux- I am aware of the fact that flux, on its own is a mathematical concept but how did it find its way into ...
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2answers
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Can $E=\frac{q}{4\pi\epsilon_0 r^2}$ be directly derived from differential form of Maxwell equations?

The electric field of a point charge $q$ is well known to be $$\mathbf E=\frac{q}{4\pi\epsilon_0 |\mathbf r|^3}\hat{\mathbf r}$$ This can be derived easily from integral form of Gauss’s law. Taking $...
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1answer
29 views

Notion of flux and field lines

I am curious about the origin of electric flux and field lines. -Flux- I am aware of the fact that flux is a mathematical concept, but how did it find its way into physics? Was it just introduced ...
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1answer
44 views

Electric field inside a uniformly charged dielectric sphere

Every basic course and book on electrostatics has this problem, to find out the electric field inside a uniformly charged sphere. The result always is $\frac{\rho r}{3 \epsilon_0}$, obtained using ...
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28 views

How to estimate distance inside an square composed of charged particles [on hold]

I have been given no info other than what I share here, and was asked to calculate the intensity of electric fields at point a and point b. And no, neither L or Q was specified. The particles weren't ...
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1answer
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Energy conservation in the combination of two coherent beams

I was asked a question today by a student that I couldn't find a satisfactory answer to. Imagine we have two identical laser beams with average electric field strength $E$. Upon combining these beams ...
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2answers
66 views

Does a neutral object has an electric field of its own?

Today in class i have learned that an electric field is basically a region around the charged particle which will cause a force to be exerted on a charged object. I was wondering what if an object is ...
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1answer
31 views

When DC current flows through salty water, how does the current flow? How can you tune the (narowness of) the path?

Consider this very simple and well-known experiment with dirty/salty water: The light bulb turns on, and current is flowing. How can you know how this current is exactly flowing, and how the electric ...
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1answer
25 views

What coordinate system to use for the position vector when finding the Electric Field or Field?

Good day all, I have seen example problems regarding line charges that will use the position vector r in rectangular, cylindrical and spherical coordinates. I know the following position vectors are:...
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1answer
36 views

Do Electromagnetic waves exert equal force on positive and negative charges?

Waves in the Electromagnetic fields propagate with the speed of light and have perpendicular E- and B-components. These components should exert a Lorentz force on a charged particle that exists in the ...
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2answers
42 views

Can a charged particle interact with its its own electromagnetic field? [duplicate]

Say an electron begin moving with velocity V back and forth very quick or at the speed of light, could it interact with its own previous pre existing electromagnetic field?
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1answer
34 views

Total internal reflection of sine wave vs smooth step function [closed]

If an electric field described by the function $$f(t)= \begin{cases} 0&\text{if}\ t<0\\ \sin(t)&\text{if}\ 0\leq t\leq \frac\pi2\\ \ 1&\text{if}\ t>\frac\pi2 \end{cases}$$ ...
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1answer
41 views

How can I detect an electric field?

I can easily detect the presence of magnetic field over a surface by using compass or by placing some iron filings. But how could we similarly detect electric field over a place?
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2answers
32 views

Velocity factor in coax cables

I mainly see the term "velocity factor" used when referring to the velocity of propagation of an electromagnetic wave front in coax cables. This velocity seems strongly dependent on the properties of ...
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1answer
32 views

Derivation of formula for electric field strength [duplicate]

I'm currently studying Cambridge A-Levels Based on the definition of electric field strength in the textbook, in which electric field strength at a point is the force per unit charge exerted on a ...
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26 views

Capacitance of coplanar copper strips with multiple dielectrica [migrated]

I want to measure the water level of an aquarium by measuring the capacitance of two coplanar copper strips on the outside of the aquarium. To design the circuit that measures the capacitance I would ...
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1answer
36 views

The electric field in the focal length of a strongly focused lens

I have a Laguerre Gaussian beam and I want to focus it by using a strongly focusing lens. But my question is that I don't know what will happen to the electric field structure in the focal length ...
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1answer
49 views

Dual finite parallel disk capacitor; estimating mathematically that the potential or field or distribution is nearly uniform from first principles

Working through Purcell. In particular, doing my best to put everything on a firm footing, mathematically, so that I can understand it. But, I have struggled all week in establishing from first ...
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4answers
75 views

Why is electric field of an infinite plate constant at all points?

I know from Gauss law, it is $\vec{E}=\dfrac{\sigma}{2 \epsilon_0}(\hat{n})$ at all points. But it doesn't make sense because of the inverse square nature of electric field which suggests if you move ...
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2answers
65 views

Electric Field between two parallel plans of opposite charge density

So considering two infinite parallel plans of opposite charge density let's say +σ for the left plan and -σ for the right plan Why is the electric field calculated this way : $$ E = σ/2εo + σ/2εo ...
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How to arrange charges on a 1d line so that the electric field along the line far away is r^-6? [closed]

My question is simple: How to arrange charges on a 1d line so that the electric field along the line far away is r^-6?e.g., we can make field falling as r^-3 by two charges(dipole field). This type ...
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1answer
30 views

Current generation

No matter the arrangement of resistors in a circuit, a battery will still produce a current as if it were connected to an imaginary combination of the individual resistors within the circuit? Can ...
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2answers
48 views

Gauss Law For Electrostatics [duplicate]

In Gauss Law for Electrostatics, Electric flux term contains Electric field due to charges that are both inside and outside the Gaussian surface. If we use Gauss Law to calculate electric field at a ...
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0answers
28 views

Electric flux over a closed surface when point charge lies on the surface

What will be the electric flux over a closed surface when point charge lies on the surface, that is neither inside nor outside? I ask this question because electric field at that point will be ...
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1answer
33 views

Why is electric field inside a charge distribution not infinite?

Let's consider electric field due to a charge distribution at a point $P$ inside the charge distribution. Due to inverse square nature of electric field, electric field due to an element volume charge ...
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0answers
27 views

The significance of the infinite electric charge relating to renormalisation in QED

This question is related Significance of electrical fields of infinite objects but is not a duplicate, imo. My question is based on reading Frank Close's book "The Infinity Puzzle", which on page 42 ...
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3answers
48 views

Atom is not neutral? [closed]

The thing that always confused me, was how can atom be electrically neutral, if electrons are closer to observer. Well, okay, I started to read a quantum mechanics book, so to clarify: there is a big ...
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0answers
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Two dimensional hyperbolic potential has no charge density but a surface charge density?

I am learning about electric potential, and I am confused about what exactly is going on in the following situation: Say we have a potential $V =- V_0 \frac{xy}{a^2}$ This means that $\nabla^2V=0$. ...
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1answer
27 views

Why do the field line asymptotes in this diagram bend?

If there is a +1 charge and another +1 charge the field lines have a vertical and horizontal asymptote. However, when the charges are uneven, the vertical asymptote is curved leftwards: I don't ...
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1answer
69 views

Electric field from a quadrupole

In the following problem, I have already solved for the value of the potential, and I would like to tackle the extra exercise, which asks for the electric field of a point quadrupole: At every ...
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0answers
35 views

Why does changing magnetic flux induce an emf? [duplicate]

What happen to charges when we change magnetic field? What is the real reason behind it?
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1answer
42 views

Electric potential everywhere around an infinite slab

The problem: Consider an infinite slab with uniform charge density $\rho$ between two planes $z=\frac{d}{2}$ and $z=-\frac{d}{2}$. Find the electric potential $V$ in the entire space and plot $V$ ...
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1answer
50 views

Can electron leave an atom due to electric field?

I know about photoelectric field, but it's about an E&M waves (photons). How about external electric\Coulombic\static field (virtual photons)? Can it turn the electron away from atom? I wonder, ...
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1answer
61 views

Non-conservative electric fields

Is the electric field produced by uniformly moving charges non-conservative? And if it is, then why?
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Enhanced electric field of nanoparticles

This is an image taken from some studies about SERS effect of very little nanoparticles ("radius" < 10 nm) involved in a surface plasmon resonance. They are immersed in an dynamic electric field ...
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1answer
36 views

All magnetic effects, simply provided by a contracted electric field?

Is the contracted electric field of constantly moving charge is what we call a magnetic field? Does the charge, that moves in a straight line has a north and south poles? Contracted electric field has ...
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1answer
43 views

I'm confused about what streamlines are in electromagnetism

In the below picture, what exactly is the streamline? Is it the three blue curves or is it the E vector drawn? Also, to calculate the equation of the streamline, we are using the ratio of the ...
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1answer
52 views

Creation of electric field inside a conductor

My book says that as soon as the two ends of a conducting wire touches the two terminals of a battery, it generates an electric field inside the conductor. Why?
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1answer
31 views

Placing a negative charge in the field of positive charge

If we put a negative charge in the field of a positive charge and I know that the two charges attract each other, will the two charges attract each other until they touch?
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3answers
49 views

How can we hold a charge to be stationary in an electric field [closed]

Suppose we have a positive point charge And we put a positive test charge in in the electric field, how can we keep this charge static, And how external work May keep it static because i think it will ...
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1answer
27 views

Why does a ionic crystal polarize more at low frequencies rather than at high ones?

And if there was a difference if the propagational mode of the electric field in the crystal is longitudinal or transverse.
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0answers
30 views

Why does electric field contracts with particle motion

Charged particle generates forces around it. The propagation of "generation" occurs with $c$ speed. When particle moves the field "moves" with it. I get troubles next - according to Lorentz boosts, ...
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0answers
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Does electric field rotates with moving electron, due to spin? Does spin influence on electric field at all? [duplicate]

When electron moves, its electric field contracts, and becomes asymmetric. If spin means that electron rotates around itself, does the electric field rotates too? Does spin influence on electric ...
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3answers
81 views

Fields $E$, $D$ and polarizaton $P$

I am studying Griffith's Introduction to Electrodynamics and having problems to grasp few things. Anyway, taking into account a problem of dielectric being put between parallel plate capacitor. ...
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0answers
37 views

Should there always be a ripple on electric field lines at а constant movement?

If you launch this applet you'll see a charge and field lines that propagate from this charge with finite speed. Why when charge moves, the lines move instantly with charge but not like below ...
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1answer
38 views

Question about Optical tweezers working principle

Why do particles on the periphery of the laser beam in optical tweezers apparatus drift to the center of the beam? What force pattern causes this pull to the center?
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How to calculate the Electric field of an cylinder with length of infinity and given charge density of the surfac? [closed]

I know how to calculate the Electric field of this example if the given variable would be the charge density of the volume but since only the charge density of the area is given, I'm very confused ...