Electric field Definition and 1000 Threads

An electric field (sometimes E-field) is the physical field that surrounds electrically-charged particles and exerts force on all other charged particles in the field, either attracting or repelling them. It also refers to the physical field for a system of charged particles. Electric fields originate from electric charges, or from time-varying magnetic fields. Electric fields and magnetic fields are both manifestations of the electromagnetic force, one of the four fundamental forces (or interactions) of nature.
Electric fields are important in many areas of physics, and are exploited practically in electrical technology. In atomic physics and chemistry, for instance, the electric field is the attractive force holding the atomic nucleus and electrons together in atoms. It is also the force responsible for chemical bonding between atoms that result in molecules.
Other applications of electric fields include motion detection via electric field proximity sensing and an increasing number of diagnostic and therapeutic medical uses.
The electric field is defined mathematically as a vector field that associates to each point in space the (electrostatic or Coulomb) force per unit of charge exerted on an infinitesimal positive test charge at rest at that point. The derived SI units for the electric field are volts per meter (V/m), exactly equivalent to newtons per coulomb (N/C).

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  1. D

    Electric field of a finite linear distribution of charge

    Hello! I do it for definition because Gauss's law not possible. I use cartesian coordinates: $$dq=\lambda dx'\text{because is only in x direction}$$ $$\vec{r'}=(x',0)$$ $$\vec{r}-\vec{r'}=(x-x',y)$$ $$\hat{r}=\frac{(x-x',y)}{\sqrt{(x-x')^{2}+y^{2}}}$$...
  2. D

    Electric field created by point charges

    Hello, I reasoned by simmetry, the two charges with value 2q not contributed at field because there are equidistant at point and are similar charges. Therefor only survival the field due to Q, using the definition for electric field of the puntual charge...
  3. askingask

    Can Spinning a Conductor Between Charged Plates Generate Current?

    If I place a conductor between charged plates, spin the conductor or plates and connect the conductor with terminals, would I generate a current?
  4. Su6had1p

    Coulomb's law to find electric field for charge density function

    The volumetric charge density is given as $$\rho(r) = \rho_0 \left(1 - \frac{ar}{R}\right)$$ What shall be the Electric field at any distance ##r## ? My approach was to directly use the coulomb's law and integrate with respect to volume. $$ \mathbf{E}(\mathbf{r}) = \frac{1}{4\pi\epsilon_0}...
  5. B

    Gauss' law for charge distribution of a point charge at the origin surrounded by an insulating sphere

    Hi I'm trying to solve this So far I have got But me not sure whether it correct or not. Maybe someone knows of a way you can check answer is correct like in math when you plug solution to solve equation? Best wishes to you
  6. C

    I Confusion regarding insulator and conductors

    In textbooks, are words such as 'metallic', 'metal', etc indicating to the person doing the problem that the material in question is a conductor? This one problem said 'metallic' and the answers were as if it were a conductor with the electric field between 2 concentric hollow spheres being 0...
  7. S

    I Electret with circular electric field

    [ Given that an "electret" can be made, that retains a persistent electric field, most often as a flat slab with a perpendicular field ] Can an electret be made with a permanent circular electric field ? Eg in a slab with the field forming a loop in the plane of the slab ? It would have to be...
  8. Heisenberg7

    B Electric Field Created by a Finite Plate

    Let's assume that we have a finite plate which is at the center of a cartesian coordinate system. Now let's define a point ##r## with coordinates ##(0, 0, z)##. My question is, can we use Gauss's law to find the electric field at this point? The direction of the electric field is going to be up...
  9. E

    I Does path independence still hold if permittivity is non-uniform?

    Consider a scenario in the picture where one half of space consists of a material with permittivity ϵ1 and the other half consists of a material with permittivity ϵ2, where ϵ1 > ϵ2. A unit positive charge is fixed at the interface between the two materials. Path1 is entirely within the material...
  10. Hellec408

    Induced charge on a conducting sphere sliced by a plane

    We are given a conducting solid sphere, and it is cut by a plane which has a minimum height r/2 from the centre of the sphere, which has radius r. A charge Q is given to the smaller part of the conductor, and it is required to find the induced charge on the curved and flat surfaces of the other...
  11. Jz21

    Electric field calculations for a spherical grid

    Hello, I need some help regarding how to calculate the needed radius to achieve 1 x 10/6 v/m on the surface of a spherical inner grid, inside a conductive vacuum chamber. I have used various equations, however I don’t know if they are very good and would like to know other methods. Thanks!
  12. E

    Electric field around a circuit

    We know that E is conservative so the integral of E around a closed loop is zero. I know this helps us (in some way, that's why i'm asking) to calculate the total voltage drop around the complete circuit (which is zero). What exactly is "E" in the integral? For example, internet says "electric...
  13. cianfa72

    I Video: 'How electricity actually works'

    Hi, I found this interesting video about How electricity actually works. The point he makes (see for example the video at minute 7:23) is that the energy in a light bulb connected to a battery is actually transferred by the electromagnetic field and not by electrons flowing through it. The...
  14. N

    Electric field at a point inside a non-uniformly charged sphere

    My solution is this: $$q = \varepsilon_0 \int E.dA$$ Based on gauss's law. Taking the derivative of both sides with respect to $$A$$ we get: $$\frac{dq}{dA} = \varepsilon_0 E$$ From chain rule: $$\frac{dq}{dA} = \frac{\frac{dq}{dr}}{\frac{dA}{dr}}$$ On the other hand: $$q = \int \rho dv = \int...
  15. akansh_karthik_1

    B Circular motion as a result of the Lorentz force

    If a charged particle moves with velocity V over a perpendicular margnetid feild B then the particle experiences lorentz force F = q(V x B). This force eventually results in what is called circular motion where the magnetic force becomes centripetal. However if the Lorentz force results in...
  16. I

    Sheet of charge - theory

    To some of these questions I can't find answers on the internet and to some I assume what the answer is but I'd still like to get a confirmation. When I am not given the thickness of the plate, does that mean that the plate is intinitely thin? What is the area of the sheet of charge when the...
  17. A

    B Understanding the electric field

    I’ve been trying to get the proper understanding of electric field. Fine I get the definition: any charge changes space around itself and thus generates electric field that acts with force on any object that’s relatively close to the charge. But first from the first, how can the FIELD act with...
  18. Z

    Why is source force + electrostatic force = 0 inside battery?

    If a battery is in a closed circuit, we have an electrostatic field ##\vec{E}## from the positive terminal to the negative terminal of the battery through the circuit outside the battery. This field generates current. Inside the battery, the electrostatic field lines go from positive to...
  19. T

    Charge on a grounded conducting sphere in a uniform electric field, after ungrounding and movement

    Question 1: The sphere is at the electric potential of the top plate. As the sphere is small with respect to the capacitor, one can consider the bottom plate to be at infinity and therefore we can use the capacitance formula as C = 4 ∏ε0 R. The charge Q is therefore Q = C (V -0) = C V...
  20. P

    I Problem with one of the premises in electrostatic pressure theory

    I have the video linked with the time stamp. . Isn't Electric Field anywhere inside the conductor zero. So there will be no electric field inside the thickness of the conductor. But he managed to integrate it somehow? he considered electric field to be changing inside the conductor that has...
  21. M

    I Work done by electric field of an irregularly shaped conductor

    I am trying to wrap my head around something and would be grateful for some insight. Specifically, why the different electric fields along different paths to different areas of an irregularly shaped conductor don't impart different energies to inflowing particles. Say we have a negatively...
  22. L

    How do we know the point of 0 electric field is on the axis?

    In many homework problems I've encountered, they all seem to assume the electric field = 0 point is along the axis of the two charges. Intuitively it kind of makes sense, but I'm looking for a solid justification for it. In other words, why can't it be off the axis of the two charges? When...
  23. flyusx

    I Thought I Understood Gauss' Law (Sheets)

    We know Gauss's law for an infinite sheet yields ##\textbf{E}=\frac{\sigma}{2\varepsilon_{0}}##. This is relatively elementary and I completely understand the derivation. This is also valid when looking at a parallel plate capacitor (the electric field is additive between the plates yielding...
  24. chrisbroward

    (Help) Surface charge density (σ) for particle to hit plate...

    I don't know if i'm exactly right. But I started with x(time) = V cos θ t which = (6810 m/s) cos (69.1°) (11.4 * 10^-3 s) is ... 27.69 m & since Electric field due to uniformly charge surface is represented by... E = (q * σ)/(2 * ε_0 * m), and since acceleration (a) can be expressed as F/m...
  25. ks81

    Electric field strength and direction problem (need help)

    E1= 9.0 x 10^9 * 10 x 10^-9 / (0.045)^2 = 45000. x cos(153.43)= E2= 9.0 x 10^9 * 10 x 10^-9 / (0.02)^2= 22500 x cos(180)= E3= 9.0 x 10^9 * 5.0 x 10^-9 / (0.04)^2= 28125 x cos(90)= ? Enet= ?
  26. yashboi123

    Electric field on the axis of a ring-shaped charged conductor

    Hello. I was wondering why do we not multiply cos(alpha) by 2. I believe we should do this since the y-components of the electric field cancel out, meaning there would be 2 x-components of the electric field(at least I think so). Currently, this derivation/answer only considers one horizontal...
  27. L

    Is This Electric Field Representation Accurate?

    I have attached an image of what *I think* the electric field looks like. Would this be correct? I am convinced about everything here, apart from the ones on the far right. All the other ones loop from the +ve charge to the -ve charge, but where do the grey lines on the right loop to (the ones...
  28. C

    E&M: Forces resulting from Charges at the Corners of a Cube

    My first attempt at solving: I divided up the point charges based on the radius away from point A. 1 charge was s*sqrt(3) away, 3 charges were s*sqrt(2) away, and 3 charges were s away from point A. q remained constant. Therefore, my F_total was: F_total = k * [(q^2 /...
  29. A

    I Simple electromagnetic wave including delay

    I want to derive the electric and magnetic field at a point around an infinitely long wire which carries a sinusoidal alternating current. And I want the answer includes the phase delay according to the limited speed of propagation of the wave. Surely the answer must satisfy the Maxwell's...
  30. Z

    I In ##\nabla\cdot\vec{E}## why can ##\nabla## pass through the integral?

    We have $$\vec{E}(\vec{r})=\frac{1}{4\pi\epsilon_0}\int_V\frac{\rho(\vec{r}')}{\eta^2}\hat{\eta}d\tau'\tag{1}$$ A few initial observations 1) I am using notation from the book Introduction to Electrodynamics by Griffiths. When considering point charges, this notation uses position vectors...
  31. A

    I Electrical breakdown in air in the presence of a single charge

    Suppose there is an electric charge of 350 micro coulombs in space. The electric field at a distance of less than one meter will be more than 3,000,000 volts/meter considering that this field is greater than the electric breakdown of air and the charge has no place to discharge, what happens...
  32. SCHROEDERFPM

    I What is the ideal fluid and setup for observing Magnetohydrodynamics?

    I have been reading about Magnetohydrodynamics and would like a bit of insight from anyone who has any knowledge on the subject. If I understand correctly when a conductive fluid is in motion it produces an electric field, and motion can be generated using a few methods one of which is a...
  33. R

    A Electric field of infinite sheet with time dependent charge

    Consider infinite charged sheet in xy plane and suppose that charge is gradually and uniformly removed from the sheet. Electric field outside the sheet obviously do not depend on x and y variables, thus the Maxwell equation divE=0 reduces to the simpler form ∂Ez/∂z=0, this means that z component...
  34. W

    I The electric field due to a dipole

    and Can someone explain how they made these equations like this? How did the radius become that equation? What formulas from algebra did they applied? I'm looking at these formulas and I don't understand how r=z+1/2*d
  35. A

    B Measuring electric field vs magnetic field

    Hello. Sorry. I am not a physicist and I have very superficial knowledge of the subject. I would like to ask a question about the practical field. I only have a device that measures the electric field. When I measure the signal coming from a cell phone tower before it is reflected from a metal...
  36. MatinSAR

    Find the Electric field due to an electric dipole at the origin

    Question : I have tried to solve but I struggle with this part: Any help would be appreciated.
  37. A

    B Why can only the electric field (E) be measured?

    I would like to consult with you about something. Mobile phone towers transmit at relatively high frequencies. From a health perspective, on the internet :) all measurement values are interpreted in microteslas. However, with the Wavecontrol probe (WPF8) I have, only the electric field (E) can...
  38. Dario56

    I How is Potential Difference Created across a Resistor?

    In a simple circuit consisted of a battery and a resistor, how is potential difference actually established on the resistor? My understanding is that battery creates the electric field which propagates through space at the speed of light. Resistor is put inside this field and therefore...
  39. L

    Electric field between parallel plates

    ^^
  40. P

    Electric field in nonmagnetic material given a magnetic field

    Hello, I am stuck on a problem that I don't quite understand, which looks like this: "Given a nonmagnetic material with the magnetic field H = 50⋅exp(−100⋅x)⋅cos(2π⋅10⁹⋅t − 200⋅x)⋅ŷ determine the electric field strength E" I don't understand how I am supposed to find the solution for this...
  41. Shreya

    Does a linearly time varying B create changing E?

    As accelerated charges produces time varying electric field which produces time varying magnetic fields and so on. I know there is something wrong with my argument, I can't point it out. Please be kind to help.
  42. L

    Electric field near conducting shell

    How would I do this question? I am having trouble figuring out what the radius is meant to be, why is it not 3R?
  43. D

    Can Homework Help Calculate the Electric Field from Two Point Charges?

  44. MatinSAR

    Finding electric field between two conducting plates using Gauss' law

    This picture is from Sears and Zemansky's University Physics. It considers ##S_1## as a gaussian surface then it finds electric field between two plates. The only thing that I cannot understand is why it doesn't consider the electric field due to negative charges on other plate. Then electric...
  45. Y

    A Electric field vs coupling between transmission lines

    Hello All, I'm trying to create equation which can describe relation between electric fields of three coupled-lines and coupling between them. Let we say that, we have thee lines having infinit length which are placed above ground plane in distance h. The distance between coupled lines is...
  46. Muhammad Usman

    Confused about direction of electric field

    TL;DR Summary: I am studying a book and at some point i couldn't able to understand a topic about Electric field hi All, Currently I am reading a book "Matters and interactions". In chapter 18 - Page 724 author asked reader to do the exercise about the electric field in the wire. here are...
  47. Saint Elmo

    I Parallel Capacitor safety at 10 micron plate spacing

    Hi all. This might be a complex thread or line of questioning if the first question passes the human safety test. I was advised to post at undergrad level. I myself am a layperson without an education in physics/maths so if anyone would find the patience to explain answers in terms a layperson...
  48. G

    B How is surface charge accumulated?

    let's discuss copper wire all along so we only focus on the specific wire. Let's discuss 2 cases(case 1 is hopefully correct, so if it is, would be good to mention it). I'm sorry that this text got so bigger(didn't expect it), but wanted to mention my thought process. Somehow, none of the...
  49. G

    B Electric Flux - confused about integrating over a tilted area

    I have been thinking today about electric flux and it got me (as always) into confusion. I love to dig deeper and sometimes, I deviate from the truth. Let's consider the tilted surface where Electric field is passing by. I'm attaching the image as well. I know that to calculate flux, we must do...
  50. putongren

    Two charged beads with a third bead in equilibrium

    Let a = distance between the charge on the left to the third bead. Since the electric field is equilibrium, we equate the electric field emanating from the left charge to the right charge at the location of the third bead. I want to try to find the ratio of d with a. E=E Kq/(d-a)^2 = K*3q/a^2...
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