What is Electric field: Definition and 1000 Discussions

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. rbsann

    Electric field calculation doubt (dipole)

    Hello all, i am having a hard time with EM, specially with the most simple concepts that i don't seem to grasp at all and the simple exercises that should be quite simple to solve. So the question is. ( i will omit the constant (1/4pieo) for practice sake When i calculate the eletric field...
  2. Noaha

    Change in direction of electric field on conductor surface

    I would like to know why electric field of EM waves changes it's direction to opposite when hitting a conductor surface. I know that electric field inside a conductor is zero but I am not able to connect these two situations.
  3. N

    How would the electric field vector vary at a large distance

    [ Moderator note- Edited to re-insert formatting template headers] Hi guys, I am stuck at this problem, Homework Statement Here it is given that an insulating sphere of radius a, carries a charge density ρ=ρ'( a^2-r^2)cosθ, when r <a. How will the leading order term for the electric field at...
  4. K

    Electric field created by point charges and conducting plane

    I came upon this: http://physics.stackexchange.com/questions/174514/will-the-electrostatic-force-between-two-charges-change-if-we-place-a-metal-plat/323006#323006 question on Physics Stackexchange which I found very interesting. The configuration is basically two positive point charges q and...
  5. Frov_ken

    Finding the power from the electric field amplitude

    Homework Statement I am modelling a ray-tracing algorithm(image method), and I am in the part where I am getting the summation of all EM "rays" hitting the receiver. I come to a problem where I can't properly convert and unsure to do so. Ideally, I should have a collection of Ei waves defined...
  6. F

    Electric field strength inside a conductor

    I read on physics.stackexchange that using Gauss Law we can prove that the electric field strength increases as the radius increases inside a metallic conductor. Later on the same website, I encountered a contradicting statement that claimed that inside a conductor, the charges aren't free to...
  7. C

    Charge density required to create an electric field

    Homework Statement Given an electric field $$\vec E(x,y,z)=\begin{pmatrix}ax^2+bz\\cy\\bx\end{pmatrix},$$with nonzero constants ##a,b,c##, I am supposed to find the charge density ##\rho(x,y,z)## which is necessary to create this field ##\vec E##. Homework Equations ##\rho=\frac{\mathrm...
  8. B

    Electric field and surface charge density problem

    Homework Statement Homework EquationsThe Attempt at a Solution I don't understand how it looks like, how to approach this problem. I think it's maybe image charge or Laplace equation
  9. P

    I The Electric field of a moving charge according to Purcell

    In Berkeley Physics Course (Volume II) on Electricity and Magnetism: https://www.scribd.com/doc/128728926/Electricity-and-Magnetism-Berkeley-Physics-Course-Purcell ...Purcell discusses the invariance of charge (Section 5.4), the electric field measured in different frames of reference (Section...
  10. A

    What is the electric field in a circular region using Faraday's law?

    Homework Statement The region is a circle with radius=a Homework Equations Using Faraday's law to find E. The Attempt at a Solution Dealing with the Left side of the second equation first 1.) Pull out the Partial/partial t because it is a constant in this equation 2.) Now I have B dot...
  11. R

    What causes a point charge to move in an electric field?

    Homework Statement : STATEMENT:[/B]A point charge at rest is released in an electric field. It will move along the electric field line...(1) REASON: The force on a point charge is along the field line...(2) State whether: A) 2 is the correct reason for(1) B) Both (1) and (2) are correct but 2 is...
  12. Berker

    Motion of 4 charges positioned in a square shape

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  13. Arman777

    Electric Potential Difference and Position Vectors: Finding Vba

    Homework Statement I have a potential Value like ##V=V(x,y,z)+C## I found ##\vec E## using partial derivative, like ##\vec E=((-∂V/∂x)i+(-∂V/∂y)j+(-∂V/∂z) k)## Theres two position vectors, ##\vec r_{a}=2i## ##\vec r_{b}=j+k## We need to find ##V_{ba}=?## Homework Equations...
  14. davidge

    Understanding the Electric Field Equation in Electromagnetism

    I was reading a book on Electromagnetism and it's said on deriving the electric field that $$\nabla \frac{1}{|x-x'|} = - \frac{x-x'}{|x-x'|^3}$$ where ##|x-x'|## is the magnitude of the distance between two point charges. I've tried to derive this result and I found that $$\nabla |x-x'| =...
  15. M

    How the wave impedance of free space works?

    Hi All, what is the reason why very close to an electromagnetic source (Fresnel Region), the wave impedance Z0 in free space for electric field and magnetic field is not the same? Z0 for magnetic field increases and for electric field decreases by increasing the distance from the source...
  16. P

    Thermal motion of an ionised gas molecule in an electric field

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  17. A

    Confusion about the magnetic field

    I'm having some confusion about the creation of magnetic field lines. How I understand it so far, is that a magnetic field is basically an electric field viewed from a relative point. I don't have a great understanding so far, as I just started to learn about it, but I've learned that objects...
  18. Arman777

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  19. P

    I Symmetry of Liénard-Wiechert Potentials

    According to responses at: http://physics.stackexchange.com/questions/93390/field-of-moving-charge-lorentzlienard-wiechert The Lorentz contraction of the electric field of a charge with uniform velocity is supposed to be symmetric across the plane pi/2 radians from the velocity vector of the...
  20. Ian Baughman

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  21. Arman777

    Uniform Slab-Finding Electric Field Using Gauss Law

    Homework Statement Uniform Slab: Consider an infinite slab of charge with thickness 2a. We choose the origin inside the slab at an equal distance from both faces (so that the faces of the slab are at z = +a and z = −a). The charge density ρ inside the slab is uniform (i.e., ρ =const). Consider a...
  22. S

    Electric Potential vs Electric Field?

    I've read that in an electric field due to it being a vector if its mirrored symmetrically the components cancel out. However, the electric potential is a scalar so the components are added not canceled out. This is consistent with one question in my physics H.W., but not for another question...
  23. FallenApple

    I Thinking about the static electric field in terms of QFT

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  24. F

    Finding magnitude and direction of an electric field

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  25. D

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  26. N

    I Relativistic charged particle in a constant uniform electric field

    I'm doing some special relativity exercises. I have to find $$x(t), v(t)$$ of a charged particle left at rest in $t=0$ in an external constant uniform electric field $$\vec{E}=E_{0} \hat{i}$$, then with that velocity I should find the Liénard–Wiechert radiated power. I will show you what I did...
  27. E

    I Hall Effect: Electric Field Direction at Equilibrium

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  28. Arman777

    Electric dipole in Uniform Electric Field (3D)

    Homework Statement An electric dipole with magnitude ##p = 0.2Cm## is placed inside a uniform electric field of ##\vec{E} = 100\vec{i} + 70\vec{j} + 40\vec{k} \frac {N} {C}##. The dipole was initially pointing along the +x direction. You then start to rotate it first on xz-plane towards...
  29. grandpa2390

    Find ELectric field in these regions of a spherical shell

    Homework Statement a thick spherical shell carries charge density k/r^2 a<r<b find E in the three regions r<a a<r<b b<r Homework Equations E dot da = Q/ε The Attempt at a Solution I can't understand why, when integrating, they choose for ii to integrate between a and r, iii and the between a...
  30. grandpa2390

    What is the Electric Field rule?

    Homework Statement so when I do a point charge and a line charge, it is just the charge over the hypotenuse squared times cos(theta) but suddenly when I get to a surface charge, I have to add the equation for the surface into the equation. Obviously, I have to integrate over the surface, but...
  31. Arman777

    Electric Field -- Rod from far away

    Homework Statement Theres a rod and has ##a## length ##L## and we want to calculaate the electric field far from rod like ##L<<a## Homework EquationsThe Attempt at a Solution I found the equation for a normal case and it was ##\frac{1}{4\pi...
  32. W

    Solving Physics Problem: Sphere & Charge Sheet

    Homework Statement A small sphere with mass 5.00×10−7 kg and charge +6.00 μC is released from rest a distance of 0.400 m above a large horizontal insulating sheet of charge that has uniform surface charge density σ = +8.00 pC/m2.Using energy methods, calculate the speed of the sphere when it is...
  33. BrainMan

    Dipole in a nonuniform electric field problem

    Homework Statement A point charge Q is held at a distance r from the center of a dipole that consists of two charges ±q separated by a distance s. The dipole is initially oriented so that Q is in the plane bisecting the dipole. Assume that r≫s. A) Immediately after the dipole is released, what...
  34. P

    Quick clarification/question on Electric Field at a point

    Homework Statement http://i.imgur.com/wBdUomo.png Another simpler way to ask the question is if the electrical potential at a point is zero, is the electric field at that point also zero? Homework Equations v = kq/r E=kq/r^2 F=qe The Attempt at a Solution http://i.imgur.com/wBdUomo.png...
  35. W

    Resultant Electric field between charges

    Homework Statement A +15 microC point charge Q1 is at a distance of 20 mm from a + 10 microC charge Q2. Fin the resultant electric field at: Ai) the midpoint between the two charges ii) at point P along the line between Q1 and Q2 which is 25 mm from Q1 and 45 mm from Q2. bi) Explain why...
  36. Iron_Man_123

    Is the force on a dipole parallel or perpendicular to the electric field?

    Homework Statement The force exerted by a uniform electric field on a dipole is: A) Parallel to the dipole moment. B) Perpendicular to the dipole moment. C) Parallel to the electric field. D) Perpendicular to the electric field. E) non of the above. Homework Equations Net force on dipole = 0 N...
  37. Cocoleia

    Electric field intensity on thin electric sheets

    Homework Statement Homework Equations The only equations I can think to use would be: But I'm not sure if they are useful or how they will help. The Attempt at a Solution I have the solution, it just isn't detailed... I don't understand where they get E=1/2ε. Should I be considering...
  38. Cocoleia

    Electric field, surface charge density

    Homework Statement Homework EquationsThe Attempt at a Solution I have the full solution, the first part being: I don't understand how they came up with the expression for Vab. I know usually ΔV=-∫E dl, but I'm not sure how they found their expression. Can someone explain? Thanks.
  39. Arman777

    Electric Field Calculation (Square Wire)

    Homework Statement Find the electric field a distance ##z## above center of a square loop of wire,each of whose sides has length ##l## and uniform charge per length ##λ## Homework Equations ##dE=\frac {1} {4πε_0} dq \frac {1} {r^2}## (magnitude) The Attempt at a Solution...
  40. C

    Finding electric potential where electric field is zero

    Homework Statement A -10.0 nC point charge and a +20.0 nC point charge are 15.0 cm apart on the x-axis. What is the electric potential at the point on the x-axis where the electric field is zero? Homework Equations ##E = k\frac{Q}{r^2}## ##V = k\frac{Q}{r}## The Attempt at a Solution I've set...
  41. Cocoleia

    Electric field above a charged square loop

    Homework Statement Homework EquationsThe Attempt at a Solution I have the complete solutions for this problem, I just don't understand them: This is the first part. I don't understand what r' is, or how we found it. Otherwise I understand the concept of the problem just not the details...
  42. T

    Electric field due to charged plates moving through a plasma

    Hi folks, this is not an actual HW question, but rather one of personal interest. I'm basically trying to understand your classic idealized parallel plate capacitor, but moving face-on through a plasma. 1. Homework Statement We have a diffuse neutral plasma made of free protons and electrons...
  43. P

    Electric field strength in an ink-jet printer

    Homework Statement One type of ink-jet printer, called an electrostatic ink-jet printer, forms the letters by using deflecting electrodes to steer charged ink drops up and down vertically as the ink jet sweeps horizontally across the page. The ink jet forms 29.0 μm diameter drops of ink...
  44. M

    Difference Electric Field Strength Point Charges vs. Plates

    Why does the electric field strength on a straight line (E = k.(Q1/d12+Q2/d22). D1,2 = distance with respect to Q1,Q2) between two point charges vary with the location on this line while the field strength between two parallel plates which remains the same anywhere between the plates...
  45. Iron_Man_123

    Electric field strength -- calculating distance from charge

    Homework Statement At a distance D from a very long (essentially infinite) uniform line of charge, the electric field strength is 1000 N/C. At what distance from the line will the field strength to be 4000 N/C? Homework Equations E=kq/r2 The Attempt at a Solution I know that E is inversely...
  46. L

    What is the electric field at this point?

    Homework Statement A charge -3.2 micro-coulombs is spread evenly throughout a rod of length (a). At a distance (b) from the rod, what is the electric field? a = 1.2 m b = 3.4 m So basically, you start at zero and then there's a line of charge horizontally to the right from 0 to 1.2 meters...
  47. Arman777

    Why electric field between two plates ##\frac {σ} {ε_0}## ?

    Why electric field between two plates ##\frac {σ} {ε_0}## ? Where is that came from ?
  48. Vanessa Avila

    Solve Proton Homework: Min Speed to Miss Lower Plate

    Homework Statement In the figure, a proton, mass 1.67×10^−27 kg, is projected horizontally midway between two parallel plates that are separated by 0.20cm, with an electrical field with magnitude 7.8×10^5N/C between the plates. If the plates are 5.40cm long, find the minimum speed of the proton...
  49. J

    Net electric field of a charged arc

    Homework Statement So this was a problem worked in class by the professor in class. Find the net electric field at the origin due to the arcs Homework Equations L=2πr/4 λ=q/L E=kQ/r2 The Attempt at a Solution So the professor gave the answer using the fromula...
  50. J

    Net Electric Field Homework Solution

    Homework Statement Homework Equations E=kq/r2 The Attempt at a Solution So i decided to do decouple the x and y values to make it simpler For Ex It became apparent through the geometry and charges that there would be no net field in the x direction For Ey: k/r2*...
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