What is E-field: Definition and 188 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. R

    Find B-Field from E-Field: Correct Answer Revealed

    Homework Statement E = 20 cos(\omegat-50x) \widehat{y} find H in free space? Homework Equations I used (\nabla X E ) = -dB/dt , and then integrated that expression with respect to t , for some reason I am getting an incorrect answer ?! The Attempt at a Solution the correct answer is H =...
  2. G

    Ampere's law, Biot-Savart law and E-field questions

    Hi, 1. Generally when using Gauss's law to e-field, I'm aware that the the surface you chose must be symmetrical and E-field is constant therefore you would only use Gauss's law for infinite sheets of charge, spherical distribution of charge and infinite line charge am i right? 2. Regarding...
  3. D

    Determining Work from E-field Graph

    Homework Statement http://img413.imageshack.us/img413/8307/prob01a.gif Determine the work done on a 0.5 µC charge moved from A to B. Homework Equations delta V= -integral(E*dl), aka the area under the curve on an E-field graph from A to B equals the potential difference. (Sorry...
  4. A

    How Do You Calculate Electric Field and Potential Between Two Charges?

    A Charge of 3.2x10-6 sits .025 m from a charge of -1.6x-6 a. Calculate the magnitude and direction of the E-filed at a point directly between the 2 charges b. calculate the electric potential (relative to V = 0 at infinity) at the point directly between the two charges c. Calculate the...
  5. X

    E-field for a rectangle of charge

    The Problem is finding the E-field at a point P that is h distance from the center of a rectangle (along a line normal to its surface) with Length L and width W with a constant charge density sigma. This is for an intro E&M class that is supposed to use up through calculus 2, and we have not...
  6. S

    E-Field in Hollow Polarized Dielectric

    Homework Statement Determine the electric field intensity at the center of a small spherical cavity cut out of a large block of dielectric in which a polarization P exists. The Attempt at a Solution charge densitysurface = P(dot)n --> charge densitysurface = P(dot)r This is about as far as...
  7. L

    E-field from Time Varying B-field of Current Loop

    I am trying to calculate the E-field from a varying B-field. The B-field is from a current loop. \vec{B}(\vec{r},t)=\vec{B_{0}}(\vec{r})Sin(\omega t) where \vec{B_{0}}= http://www.netdenizen.com/emagnet/offaxis/iloopoffaxis.htm" Now since B is varying with time there should be an electric...
  8. E

    Getting E-Field from magnetic field intensity, H

    Homework Statement Given the magnetic field intensity, H, find E. H=\hat{y}6cos(2z)sin((2x10^7)t - 0.1x) Homework Equations \nabla \times E = \frac{- \partial B}{\partial t} The Attempt at a Solution Since we have H, we can use the relationship that \muH = B and then take the...
  9. U

    E-field strong enough to rip all electrons from copper atoms

    Not just free electrons, ALL electrons. How strong would that be?
  10. N

    E, FDAC Solving E-Field with Charges

    [SOLVED] E-field with charges I've tried this 8 times and have 2 tries left, Looking for some hints Homework Statement The figure shows the E-field in the plane of two point charges. (Give ALL correct answers, i.e., B, AC, BCD...) A) Q1 is positive. B) A - charge placed at `a' would move...
  11. T

    What is the electric field at the center of curvature of an arc?

    Homework Statement Determine the field at the center of curvature of an arc of arbitary angle \alpha (\alpha is with the x-axis) Homework Equations E=\frac{kQ}{R^2}\widehat{r} S=R\alpha \lambda=\frac{Q}{S} The Attempt at a Solution I divide the arc into small pieces ds...
  12. J

    How Does Gauss's Law Apply to Electric Fields at Points P2 and P3?

    [SOLVED] Gauss and E-Field Homework Statement http://img443.imageshack.us/img443/9452/eletroof9.th.png My main problem with this problem is finding the electric field at Point 2 (P2) Homework Equations The Attempt at a Solution I derived the electric field using Gauss's Law for a...
  13. R

    E-field between insulator and conductor

    Homework Statement I have a slab of conductor on the ground with thickness, a, and it extends in all directions infinitely. Then I have a slab of insulator above the conductor of thickness, a, and it also extends infinitely in all directions. The two slabs are a distance, 2a, from each...
  14. J

    Calculating E-Field Close to a Metal Plate from an Infinite Charged Rod

    Homework Statement An infinite, thin, uniformly charged rod (charge density lamda) is situated parallel to a metal plate at a distance d above it. Calculate the E-field close to the surface of the plane as a function of perpendicular distance to the rod. The Attempt at a Solution I...
  15. P

    E-field at the center of a semicircle

    [SOLVED] E-field at the center of a semicircle Homework Statement Calculate E at center of semicircle: A uniformly charged insulating rod of length L = 12 cm is bent into the shape of a semicircle as shown. The rod has a total charge of Q = -6 nC. Find the magnitude of the electric...
  16. F

    E-field lowering of ionization potential

    When an electric field is high enough, electrons are not so easily confined to molecules or atoms. This has been the basis of field ionization for mass spectrometry. But what if the field is not enough to ionize, but close. Would it be easier to ionize the atom or molecule with less energy? Any...
  17. nicksauce

    Electric Field Above Square: Find E-Field at z Height

    Homework Statement Find the electric field a height z above a square of side length a with uniform surface charge \sigmaHomework Equations The Attempt at a Solution E=\frac{z\sigma}{4\pi\epsilon_0}\int^{a/2}_{-a/2}\int^{a/2}_{-a/2}\frac{dx dy}{(x^2+y^2+z^2)^{3/2}} (in the z direction)...
  18. C

    E-Field Calc: Hollow Cylinder E-Fields

    Can a hollow cylinder of known radius, height and charge be treated as a line of charge if one is trying to find the E-field at an arbitrary perpendicular distance from the center of the flat surface?
  19. P

    Equation for magnetic moment, E-field and B-field

    Hi! When a charge/current moves in a closed loop, a magnetic moment is generated. Is there any formula for connecting the magnetic moment to E-field and B-field? Patrick
  20. M

    How Do Charge and Mass Affect Ion Acceleration in an Electric Field?

    Homework Statement Assuming equal masses, how would the detection times of 3H+ and 3He+ compare [as they're both accelerated toward a detector in the direction of a constant E field]? A) 3H+ would have a longer flight time than 3He+. B) 3H+ would have a shorter flight time than...
  21. I

    E-field due to a large circular plane of uniform distribution

    E-field due to a large circular plane of uniform distribution! Hi Imagine i have a circular disc of radius R with uniform charge density, and a small charge x meters away from its center. The idea is to calculate the e field for this charged disc on the small charge. I can solve this problem...
  22. T

    Magnetism (Charge, E-field, potential difference, mass) - A bit confused

    Homework Statement Image: http://img.photobucket.com/albums/v696/talimtails/PP23.jpg A particle with unknown mass and charge moves with a constant speed v = 1.9 x 10^6 m/s as it passes undeflected through a pair of parallel plates, as shown above. The plates are separated by a distance d...
  23. P

    E-field of non-conducting, nonuniform shell

    Homework Statement Right have a shell that has a volym charge distribution P=(G/r^2) and with inner radius a and outer radius b. Now what is the e-field at r<a, a<r<b, r>b Homework Equations gauss's law: surfaceint[E.da]=Qenclosed/epsilon0 Qenc=volymint[PdV) The...
  24. Y

    Time varying e-field polarization

    i'm in a bit of a tizzy with an optics class question... it goes like this: under the application of a time varying electric field the induced polarization in a dielectric may be described by the equation: P = [(Ne^2)/(-m(omega)^2-im(omega)(gamma)+k)][E+(1/3(permittivity))P] where the...
  25. N

    E-field of an ununiformly-charged rod

    ballistic particle and electric field Throughout space there is a uniform electric field in the -y direction of strength E = 450 N/C. There is no gravity. At t = 0, a particle with mass m = 5 g and charge q = -11 µC is at the origin moving with a velocity v0 = 35 m/s at an angle q = 25° above...
  26. S

    Decaying E-Field: Spatially Uniform in Conductors

    We are asked to show that we can have a "spatially uniform E-field" in a conductor according to E=Eo*exp(-t/tau) where tau=ErEo/sigma where Er is the relative permittivity and sigma is the conductivity. I know we need to use curl(H) = ErEo*dE/dt + sigma*E and for some reason we say that...
  27. S

    Why Is the Potential Zero on the Surface of a Conducting Sphere in an E-Field?

    I've solved an electrostatics problem where we have to find the surface charge density on a conducting sphere in a previously uniform E-Field, but I had to assume that V=0 on the surface of the cylinder, and I'm not sure why this is the case. I know that E=0 inside, so the potential should be...
  28. T

    Finding the E-Field between parallel plates

    I have a positive and a negative charged plate running parallel to one another. To find the Electric Field to the left of the plates, I say: E dot dA = Qenclosed / permittivity Then E times 2pi(r) = Qenclosed / Permittivity then E = Qenclosed / 2pi(r) x Permittivity and since Qenclosed...
  29. J

    What Is the Peak Value of the E-Field If the Magnetic Field Is 2 x 10^-7 T?

    Hi, My Question: If the peak value of the magnetic field of an EM wave is 2 x 10^-7 T. Calculate the peak value of the E-field. Work: C=E/B so, 3*10^8 m/s=(E)/(2*10^-7 T) (3*10^8 m/s)(2*10^-7 T)=E E= 60 N/C Is this right ? Thank You
  30. M

    Ranking the E-field from a graph alittle confused.

    Figure 24-27 gives the electric potential V as a function of x. Figure (a) Rank the five regions according to the magnitude of the x component of the electric field within them, greatest first (use only the symbols > or =, for example 2=4>1=3>5). I got the other 2 parts (b) and (c)...
  31. F

    E-Field Lines and Equipotential Surfaces

    Hey all, I'm a bit confused over an experiment in which we mapped Equipotential Surfaces to then use to draw Electric Field lines using electrodes placed into water to act as a dipole. Along with this, we also had to place a circular conductor and insulator (both uncharged) into the water as...
  32. M

    Finding E-field of 2 concentric clyinders

    Hello everyone. I'm having troubles figuring out the E-field of two long, charged, thin-walled, concentric clyinders. Its question #6 on the picutre. The image has my work, it seems my apporach was too simplistic, because the problem gives you 2 radi, but then gives u another 2 radi to find...
  33. L

    How Do Electric Fields Behave in Nested Spherical Charge Distributions?

    ok, I have an exam on Monday and I know the prof is going to give a problem where we have inner solid sphere of uniform charge density (+), and this sphere is surrounded by an outer spherical shell with a uniform surface charge density (-). He wants us to calculate the e-field "everywhere" with...
  34. L

    Understanding E-Fields and Their Applications in Physics

    ok, so I have a physics test monday, and I know the prof will make us calculate the e-fields, and voltages everywhere is space produced by various objects with uniform charge densities using Gauss's law. So, he wants us to derive a general expression that describes the e-field and voltage...
  35. F

    E-Field of non-conducting plane

    Three very large sheets are separated by equal distances of 20.0 cm (Fig. 22-42). The first and third sheets are very thin and nonconducting and have surface charge densities of +6.50 µC/m2 and -6.50 µC/m2, respectively. The middle sheet is conducting but has no net charge...
  36. L

    E-field for infinitely long cylinder

    ifthis is an infinitely long cylinder how can i derive an equation for finding the magnitude of the electric field? i have the answer which is E=2*pi*rho*K*r but i don't understand how they got it.
  37. E

    Calculating E-field of Uniformly Charged Sphere

    I need to calculate the electric field both inside and outside a sphere with a charge density p. The trick is I am required to use Coulomb's Law. I cannot appeal to Gauss' Law. My instructor suggests considering the electric field due to a ring of charge. Then to use that result to find...
  38. Z

    Solving an E-Field Question: Magnitude of Electric Field Calculation

    [SOLVED] E-field question I'm new here but hope that's not a problem. I have an e-field problem that i was wondering about. Now this is how it was presendetd to me. A charge of uniform density 4.0 nC/m is distributed along the x-axis from x=-2.0 m to x=+3.0m. What is the magnitude of...
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