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. P

    Finding magnitude of two charge given midpoint

    Homework Statement Two positive point charges, A and B are 6m apart. The electric field intensity at point C, midway between the two charges is 5 N/C directed towards B and the potential at the same point is 45V. Find the magnitude of A and the magnitude of B. Homework Equations E = kQ/r2 The...
  2. AdrianMachin

    Confusion over electric field inside a charged shell

    I've got confused over a topic in my physics textbook (Fundamentals of Physics). The textbook says if a charged particle is enclosed by a shell of uniform charge, there is no electrostatic force on the particle from the shell. I don't firmly get this, as the book uses a confusing reasoning for...
  3. K

    Electric field due to plane of charge

    Why the gaussian surface is "A" instead of "2A" on the right-hand side?(the photo attached below) Due to the thickness of the sheet? I usually find that E=σ/2ϵ0 is being frequently used but we hardly use E=σ/ϵ0. When can I directly apply the equation E=σ/ϵ0 ?
  4. claudius

    The KE of an electron accelerated by an electric field

    Hello, An electron accelerated through a pd of V volts will have a K.E = eV. Why isn't the K.E less than this considering that some of the work done by the field has been radiated as electromagnetic waves by the accelerating electron ? All insights very welcome.
  5. 1

    Boundary conditions of a plane wave on a conductor

    Homework Statement Consider a plane monochromatic wave incident on a flat conducting surface. The incidence angle is ##θ##. The wave is polarized perpendicular to the plane of incidence. Find the radiation pressure (time-averaged force per unit area) exerted on the surface. Homework Equations...
  6. G

    Gauss' Law - Electric Field for a Charged Metal Plate

    Homework Statement An infinite metal plate has a surface density of charge σL=-6μC/m² , Left side and a surface density Of load σR=+4μC/m² , in the right side. A Gaussian surface In the form of a circular cylinder, with area A 12 cm², is Located with the left side inside the plaque and a thin...
  7. R

    Allowed EM Waveforms: Which Ones?

    Homework Statement which of the following proposed space-time dependent electric fields in vacuum is/are allowed by the equations of EM theory? a) $$E_x=E_1\sin(kz-wt),E_y=E_2\sin(kz-wt),E_z=0$$ b) $$E_x=E_1\sin(kz-wt),E_y=2E_1\cos(kz-wt),E_z=0$$ c)...
  8. dbuhtoia

    Electric field with three charges and a point

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  9. M

    Electric field Pre-lab annotation

    Homework Statement I am working on annotating the pre-lab for this Electric Field lab and needs to have some help look at my work. The second question of the Pre-Lab is comparing the answers between two persons Kate and Victor. Based ib this diagram below * o (-1) * * o (+1)...
  10. S

    What is the magnitude of the electric field (rod)?

    Homework Statement Two thin glass rods are placed side by side 4.70 cm apart as shown in the diagram below. They are each 11.3 cm long and are uniformly charged to +10.4 nC . Answer the questions below regarding the electric field along a line which is drawn through the middle of the two glass...
  11. U

    Field along vertical axis to hemispherical shell

    Homework Statement A hemispherical shell has radius ##R## and uniform charge density ##\sigma##. FInd the electric field at a point on the symmetry axis, at position ##z## relative to the center, for any ##z## value from ##-\infty## to ##\infty##. The Attempt at a Solution Let ##\theta## be...
  12. J

    Electric Field and Potential Scenario

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  13. P

    Electric Field of Uniformly Charged Rod at bisector

    Homework Statement (Taken from Serway and Jewett Chapter 23, Q44, 9th Edition) A thin rod of length ## l ## and uniform charge per unit length ##λ## lies along the x-axis as shown in the image attached. (a) Show that the electric field at P, a distance d from the rod along its perpendicular...
  14. P

    Electric field of a moving charge?

    I have a moving charge in a generic motion, and I pick a point p, how do I get the electric field caused by the charge on point p, at any time? Can I use the coulomb definition of electric field that relates it's strenght with the Distance? Or does that law works only when the charge is static...
  15. Nabin kalauni

    Is electric field always 0 if potential at a point is 0?

    I understand that if electric field at any point is 0, it implies that potential is constant not necessarily 0. But what if the potential at a point is 0? Does it imply that electric field is 0? Me and my friend had an argument and I am in the favour of electric field not being 0. Do I win guys...
  16. 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...
  17. 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.
  18. 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...
  19. 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...
  20. 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...
  21. 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...
  22. C

    Charge density required to create an electric field

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  23. 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
  24. P

    I The Electric field of a moving charge according to Purcell

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  25. A

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  26. R

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

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  27. Berker

    Motion of 4 charges positioned in a square shape

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  28. Arman777

    Electric Potential Difference and Position Vectors: Finding Vba

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  29. 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'| =...
  30. 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...
  31. P

    Thermal motion of an ionised gas molecule in an electric field

    What I want to discuss here is what happens to the thermal velocity when an ionised gas molecule has been put into an electric field. Due to the charge (e) and potential difference (V), how much velocity has been gained by the ion can be calculated easily.eV = ½mv2 Where e is the charge of the...
  32. 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...
  33. Arman777

    Dipole Oscillation İn Electric Field

    Homework Statement Electric Dipole makes small oscillation is electric field find its ##ω## Homework Equations ##τ=pEsinθ## ##τ=I∝## The Attempt at a Solution ##τ=pEsinθ## ##τ=I∝## so ##pEsinθ=I∝## which that's...
  34. 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...
  35. Ian Baughman

    Understanding Electromagnetic Waves

    So I know that EM waves travel perpendicular to the electric and magnetic fields which are also perpendicular to each other. What I'm having difficulty understanding is since light is an EM wave and can travel through the vacuum of space, does that imply that everywhere in the universe there is...
  36. 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...
  37. 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...
  38. FallenApple

    I Thinking about the static electric field in terms of QFT

    So according to classical electrodynamics, an electron would produce an electric field that is a physical entity in and of itself. This field has momentum so when a test charge is placed within this vicinity, it would be affected by the field itself, not the electron. But what about the QFT way...
  39. F

    Finding magnitude and direction of an electric field

    Homework Statement A spaceship encounters a single plane of charged particles, with the charge per unit area equal to σ. The electric field a short distance above the plane has magnitude _____ and is directed _____ to the plane. a) σ/2∈0, parallel b) σ/2∈0, perpendicular c) σ/∈0, parallel...
  40. D

    Calculating Electric Field Strength and Direction for a Negative Charge

    I think I have this correct, could someone please verify? I compared answers with a friend who got 2.0 x 106 N/C to the left, and I can't figure out how they got that answer, so I'm hoping mine is right... 1. Homework Statement A negative charge of 3.5 × 10–8 C experiences a force of 0.070 N...
  41. 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...
  42. E

    I Hall Effect: Electric Field Direction at Equilibrium

    I have a good understanding on the hall effect. However, I was told by my tutor that the electric field direction at equilibrium remains pointing in the negative side of the conducting material and the force it generated is canceled out. But further reading online text, the electric field...
  43. 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...
  44. 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...
  45. 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...
  46. 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...
  47. 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...
  48. 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...
  49. 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...
  50. 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...
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