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. NiendorfPhysics

    Find A Such that the Electric Field is Constant

    Homework Statement The Spherical region a<r<b carries a charge per unit volume of $$\frac{A}{r}$$, where A is constant. At the center there is a point charge q. Find A such that the Electric field in a<r<b is constant. Homework Equations Law of superposition and $$E=\frac{kq}{r^2}$$ The...
  2. Tazerfish

    Phase difference between magnetic and electric field

    When solving the differential equations for an electromagnetic wave you get out that the electric and magnetic field oscillate in phase. But when considering a oscillating dipole, the electric and magnetic field at a point close to the dipole are a quater period out of phase. Can someone please...
  3. G

    How can voltage drop be zero if E-field isn't?

    Hi. I learned that in an ideal conductor in a circuit, the voltage drop is zero. But how does this agree with the basic definition of voltage $$U_{AB}=\int_A^B \vec{E}\cdot d\vec{s}\enspace ?$$ The electric field inside a conductor only vanishes in static conditions, but in an electric circuit...
  4. T

    Electrostatics/Electric Field Question

    Homework Statement What is the magnitude E of the electric field at point P? Throughout this part, express your answers in terms of the constant k, defined by k = 1/(4πE0) To solve this question, I am trying to walk through the hint process. Question 1: Find the magnitude dE of the electric...
  5. Narayanan KR

    Will capacitors react to external electric field

    1. Passage of current via coil creates magnetic field (fig a), similarly external magnetic field linked to coil when changed created electric current in the circuit connected ( Faraday's em induction fig b). 2. Charging of capacitor using voltage source creates electric field in the capacitor...
  6. T

    Weird thinking of electric field inside a hollow cylinder.

    While I was studying with electric field about cylinder, I learned that for a very long cylinder, the electric field in the hollow of cylinder will be zero. http://physics.stackexchange.com/questions/156789/electric-field-of-hollow-cylinder However, I couldn't accept this intuitively, and...
  7. G

    Does a lightning rod also avoid lightning?

    Hi. I understand a lightning rod reroutes the current of a lightning around an object, e.g. building. The lightning will preferably strike the rod because the electric field is strong at sharp points and the air is more likely to be ionized there. But does it also avoid lightning by giving off...
  8. N

    Finding the Electric field at the Origin

    Homework Statement I'm trying to find the electric field at the origin <0, 0, 0> due to a quarter of a ring with +Q charges on it. The quarter of the ring lies on the +y-axis. Due to symmetry, the x-components of the electric field will cancel out, leaving only the y-component of the electric...
  9. W

    Electric field inside and outside a sphere (Not Gauss)

    Find E(r) inside and outside a uniformly charged spherical volume by superposing the electric fields produced by a collection of uniformly charged disks. a+b) Given equations, sketch of problem This is the equation in the handbook for a disk (but in the exercises the z becomes x, without loss of...
  10. S

    Electric field strength with distance

    Consider Gauss's law in ##1## space and ##1## time dimension. In this case, ##\int\ \vec{E}\cdot{d\vec{A}}=\displaystyle{\frac{Q}{\epsilon_{0}}} \implies 2 E =\displaystyle{\frac{Q}{\epsilon_{0}}} \implies E =\displaystyle{\frac{Q}{2\epsilon_{0}}}##, where the factor of ##2## comes from the...
  11. Jabbar

    Electric field due to a charged rod

    Homework Statement https://gyazo.com/d502fb408d6224ffa70700cf047bad20 (link to problem: #4). [moderator edit: Image inserted for clarity] A total charge Q is distributed uniformly over rod length L. The rod is aligned on the x-axis, with one end at the origin and the other at point x=L. a)...
  12. A

    Understanding Electric Field Screening in Materials

    Can anyone explain in simple terms what the term screening means? My intuition is that a metal is a good screener because in the presence of an external electric field its free electrons will rearrange themselves such that the electric field is zero inside the metal. But I am having a hard time...
  13. arpon

    Electric field outside conductor

    Homework Statement A long metal pipe of square cross-section is grounded on three sides, while the fourth (which is insulated from the rest) is maintained at constant potential ##V_0##. What is the electric field just outside the section opposite to ##V_0##? Homework EquationsThe Attempt at a...
  14. Blockade

    Is the total electric field of two opposite charges 0?

    Let's say you have two particles that are the same in magnitude but have opposite charges like the equation down below: E1 = -q*k/r^2 E2 = q*k/r^2 ETotal = q*k/r^2 + -q*k/r^2 = 0 Does this mean that the electric field of both these charges cancel out each other? Then what is the electric...
  15. E

    Force against electric field

    Hi, I found this on http://farside.ph.utexas.edu/teaching/302l/lectures/node32.html "Consider a charge placed in a uniform electric field (e.g., the field between two oppositely charged, parallel conducting plates). Suppose that we very slowly displace the charge by a vector displacement in...
  16. T

    Electric field inside and outside a charged cylinder

    Homework Statement WITHOUT using Gauss's law calculate the electric field at all points outside and inside an infinite cylinder with circular cross section of radius b and charge density ρ Hint: Use cylindrical coordinates and place the target charge on the x axis..Homework Equations E =...
  17. S

    Electric field in an arbitrary number of dimensions

    I am looking to use Gauss's law to find the electric field in ##1+1## dimensional spacetime: ##\int \vec{E}\cdot d\vec{A}=\frac{Q}{\epsilon_{0}}## Now, for a point charge in ##1+1## dimensional spacetime, the Gaussian surface is the two endpoints (a distance ##r## away from the point charge)...
  18. S

    Time-Varying Electric Field in Parallel Plate Capacitor

    Hi, A time-varying (sinusoidal) voltage source is applied to a parallel plate capacitor of length d. Then the E field will vary according to E(t) = V(t)/d. However, this suggests that, for any given time, the E field is constant with respect to spatial coordinates. Therefore, the curl of E is...
  19. M

    Where is the net electric field zero?

    Homework Statement Particle 1 of charge +4.0 μC and particle 2 of charge +1.0 μC are held at separation L=10.0 cm on an x axis. Particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero. In the included figure, particle 1 is...
  20. M

    Name For (Limit) Points In An Electric Field Plot ....

    Homework Statement I'm looking at an electric field plot around four (4) + and - point charges in free space. There are several points where the electric fields come together and make right-angled turns (in the limit). Is there a name for these points? Especially is there a traditional name for...
  21. G

    I Ontology of wavefunction vs. ontology of electric field

    Hi. Different interpretations of QM have different opinions about the ontology of the wavefunction, i.e. if it really, physically exists or if it is "just" a mathematical tool needed to calculate the outcome of measurements. The QM interpretations comparison table on Wikipedia summarises the...
  22. I

    What is the strength of the electric field 0.1 mm above the

    Homework Statement [/B] A thin, horizontal, 11-cm-diameter copper plate is charged to 4.3 nC . Assume that the electrons are uniformly distributed on the surface. What is the strength of the electric field 0.1 mm above the center of the top surface of the plate?Homework Equations [/B] E=...
  23. N

    Calculating Electric Field from a Dipole: Is This Equation Accurate?

    Is this the correct equation to find the electric field at point p from a dipole?
  24. G

    What do electric field lines look like for two metal plates?

    Hello. I'm now taking accelerator physics class and the lectures said in the thermionic electron gun, anode metal mesh should be grounded in order to prevent electrons which traveled beyond the mesh from coming back due to the electric field lines. Without grounding of the anode, I believe...
  25. A

    Electron released into an electric field from rest

    Homework Statement An electron is released from rest in a weak electric field given by = -2.70 10-10 N/C [PLAIN]http://www.webassign.net/images/lowercase/jhatbold.svg. After the electron has traveled a vertical distance of 1.4µm, what is its speed? (Do not neglect the gravitational force on...
  26. O

    Calculate net charge with nonuniform electric field

    Homework Statement In a cubical volume, 1.05 m on a side, the electric field is given by the formula below, where E0 = 1.25 N/C and a = 1.05 m. = E0(1 + z/a) i + E0(z/a) j The cube has its sides parallel to the coordinate axes, see the figure. Determine the net charge within the cube...
  27. O

    Nonconducting spherical shell with uniform charge

    Homework Statement Suppose the nonconducting sphere of Example 22-4 has a spherical cavity of radius r1 centered at the sphere's center (see the figure). Assuming the charge Q is distributed uniformly in the "shell" (between r = r1 and r = r0), determine the electric field as a function of r...
  28. O

    Electrons moving in an electric field

    Homework Statement Suppose electrons enter the electric field midway between two plates at an angle θ0 to the horizontal, as shown in the figure, where L = 5.1 cm and H = 1.1 cm. The path is symmetrical, so they leave at the same angle θ0 and just barely miss the top plate. What is θ0? Ignore...
  29. Frankenstein19

    Question about electric field of a point figure in book

    I'm studying for my physics exam and there is a figure on the book physics for scientists and engineers 4th edition by giancoli that i just don't understand. I know that the electric field of a negative charge points toward it and the electric field of a positive charge points away from it Also...
  30. twist.1995

    Electric field discontinuity in a spherical shell?

    Homework Statement Lets say, there is a non-uniform charge distribution, given as in a spherical shell that has a cavity with radius a and the radius b to the outer surface. I am wondering if the field is discontinuous just on the surface of this sphere. Homework Equations...
  31. RJLiberator

    Semi-circle linear charge Electric Field

    Homework Statement A semi-circle of radius R has a charge Q uniformly distributed over its length, which provides a line charge density λ. Determine E at the origin. Homework EquationsThe Attempt at a Solution https://www.physicsforums.com/attachments/105239 I can tell by argument of...
  32. dumbdumNotSmart

    Electric Field in a cavity of a charged sphere

    NOTE: Other threads suggest solving it with Gauss' Law. I'd like to see an approach through direct integration, no full followthrough necessary.. 1. Homework Statement Consider a sphere with a uniform distribution of charge ρ (ro). Inside the sphere is a cavity (spherical). Calculate the...
  33. M

    Electric Field of Plate to a Point

    Homework Statement [/B] A square plate of side-length L, charged with uniform surface charge density η. It is centred at x = y = z = 0 and orientated in the z = 0 plane. The task is to determine the z-component of the electric field at the point r(x, y, z) = r(x, 0, d), offset along the...
  34. J

    Infinitely charged wire and moving charge

    Homework Statement There's a uniform infinite line charge with the charge density λ. A point particle with charge q moves with a velocity v parellel to infinite line. What is force exerted on point particle? What is magnetic field seen in ths moving frame(particle frame)? Homework Equations...
  35. G

    Uniform E field for spherical shell.

    Homework Statement In the figure a nonconducting spherical shell of inner radius a = 2.07 cm and outer radius b = 2.51 cm has (within its thickness) a positive volume charge density ρ = A/r, where A is a constant and r is the distance from the center of the shell. In addition, a small ball of...
  36. J

    How to calculate the Electric Field due to Capacitors?

    I have a problem that I have encountered during research. The setup for this scenario is that I am placing two contacts on top of a piece of diamond. What I need to be able to do is calculate the Electric Field at a point within the diamond when I apply a voltage to the contact. The point of...
  37. The Bill

    I Visualizations of a hydrogen atom in an external electric field

    I'd like to see some 3D visualizations of what the wave functions of the electron and proton in a hydrogen atom would look like in different applied electric fields. Say, have a reference image at 0V, then images at various voltages where the wave functions look interesting or just illustrative...
  38. O

    Why does a voltmeter measure a voltage across inductor?

    The potential difference across an inductor is supposed to be zero, but a voltmeter measures it to be L*dI/dt. Also, if the p.d is zero then the electric field in the wires of the coil will be zero and in that case, why should charges flow at all? What am I missing?
  39. A

    Finding the Electric Field of a Parallel Plate Capacitor

    Homework Statement An electron is launched at a 45∘ angle and a speed of Vo = 5.0×10^6 m/s from the positive plate of the parallel-plate capacitor towards the negative plate. The electron lands 4.0 cm away. Homework Equations F = ma = qE v = d/t s = vt -(1/2)at^2 x = 0.04 m The Attempt...
  40. A

    Finding the Electric Field at the Midpoint of two rings

    Homework Statement Hello, Two 10-cm-diameter charged rings face each other, 20 cm apart. The left ring is charged to -22 nC and the right ring is charged to +22 nC . What is the magnitude of the electric field E⃗ at the midpoint between the two rings? Homework Equations [/B] E = Kq/r^2 K =...
  41. A

    Calculating Electric Flux Through a Rectangle with Given Electric Field

    Homework Statement Hello, A 3.60cm x 4.50cm rectangle lies in the xy-plane. What is the electric flux through the rectangle if E=(80.0i + 50k) N/C ?Homework Equations Φ = E * A =EAcos(θ) The Attempt at a Solution My attempt: First convert the rectangle units from cm to m. 4.50cm = 0.045m...
  42. J

    Electric Field Energy Density: Plates of Q & A

    Homework Statement Two large non-conducting plates of surface area A=.025m^2 carry equal but opposite charges Q = 75microC. What is the energy density of the electric field between the two plates. Homework Equations I wrote the equations on my attempt. This was a multiple choice problem...
  43. P

    Electric Field Around A Dipole?

    http://imgur.com/48cLE6q I can't follow this. Did my teacher make a mistake? Why are all the charges 2?
  44. P

    Electric field given a time-dependent magnetic field

    I suppose that my main question is how to find the induced electric field given a time-dependent magnetic field, but i will demonstrate my question with an example: I constructed a simple magnetic field B = b*tz , permeating the whole space. The induced electric field will lie in the xy...
  45. P

    1A caused by half the charge density at twice the velocity

    In the situation consisting of a steady current of 1A in an arbitrary closed path, what would the consequences be for the electric field if the drift velocity was non-uniform along the path due to non-uniform carrier density? This would be a case of a "uniform" 1 amp, but where the charge...
  46. J

    Confused about electric potential and electric field

    I get easily confused when asked questions about electric field. One question that is bothering me is... Is it possible to have 0 electric field at a point, but at the same point have electric potential? I've read that the answer is yes, there can be a potential without a electric field, but...
  47. O

    I Finding Magnetic Field from Electric Field: A Classical Physics Problem

    Hey guys, i just came across this on my classical physics course. So, I'm given that: E(z, t) = {E_{0}}sin(wt)sin(kz)\widehat{x}, and I'm supposed to find an expression for the associated magnetic field B. Usually, i just find the propagation direction, and do it's cross product with the...
  48. Magnetic Boy

    Electric field calculated by gauss law

    Which one is correct?? 1) electric field calculated by gauss law is the field due to charges inside the closed surface. 2) the flux of the electric field through a closed surface due to all charges is equal to the flux due to charges enclosed by the surface
  49. NicolasPan

    Find the electric field of a uniformly polarized sphere

    Homework Statement We want to calculate the field of a uniformly polarized sphere of radius=R Homework Equations V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \oint_{S} \frac{\sigma_{b}}{r} da' + \int_{V} \frac{\rho_{b}}{r} d\tau' The Attempt at a Solution i)I know that \sigma_{b} = P...
  50. C

    Understanding the Direction of Electric Fields: A Question of Convention?

    Hello. I have a doubt regarding the direccion of the electric field in a point from a source charges. Let be a charge in the left of the plane. In a point to the right of the charge, the direction of the electric field vector is to the right. If the charge is negative, the direction of the...
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