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. M

    Charge & E-Field: Sum of Vectors of 3 different charge

    A positively charged particle is placed along the positive x-axis and a particle carrying a negative charge of equal magnitude is placed at equal distance from the origin along the negative x axis. A third particle carrying a positive charge is placed on the y axis. The vector sum of the forces...
  2. sunrah

    Dielectric sphere in constant E-field

    Homework Statement Given a dielectric sphere with relative permittivity = ε in a homogeneous E-field: \vec{E_{0}} = E \vec{e_{z}}. The E-field causes a homogeneous polarisation (dipole density) of \vec{p} = \frac{vec{P}}{V} with big P the dipole moment vector. The total electric field...
  3. L

    E-Field Breakdown: Realistic Values in Air & FR4

    What is the realistic break down value for E field in air. Text books say its 3*10^6 V/m But there are many websites, which go down to 1*10^6 V/m. If there is a dielectric like FR4, then the break down increases V=ε E*d ?, where ε is the dielectric constant for FR4.
  4. A

    E-field of a molecule on a point

    Homework Statement http://postimage.org/image/cky823nof/ Homework EquationsE=kq/r^2 The Attempt at a Solution I figured I would just find the electric field produced at point * by each individual charge and then add them. For example if I were to set E1 to be the top molecule the field...
  5. R

    Calculating diameter of a different type of wire with same current and e-field

    Homework Statement What diameter should the nichrome wire in the figure be in order for the electric field strength to be the same in both wires? Homework Equations σ = 1/ρ J = σ*E...I/A = σ*E...I = σ*E*A Then, equate the current equations for each wire. The Attempt at a...
  6. L

    Milikin Drop experiment change of charge with E-Field

    Homework Statement In my honours lab we are performing the Milikin drop experiment, and we've come into a slight problem, where when calculating the radius of the drops and the charge on the drops, the charge seems to vary with change in E-field. When performing the experiment we first...
  7. M

    Magnitude and Direction of E-field at a Point Due to a Charged Rod

    Homework Statement There is a non-conducting charged rod with length L=.0815(m) and linear charge density λ=-5.9x10-14(C/m). The rod is placed parallel to and on the x-axis, and at a distance a=.12(m) from the right-most end of the rod is point P. Calculate the magnitude and direction of E...
  8. jegues

    Uniformly Polarized disk on a conducting plane (E-Field)

    Homework Statement A uniformly polarized dielectric disk surrounded by air is lying at a conducting plane, as shown in the figure. The polarization vector in the is, \vec{P} = P \hat{k}, the disk radius is a, and the thickness d. Calculate the electric field intensity vector along the...
  9. C

    How Do Surface Charges Affect E-field Patterns in Prisms and Cubes?

    Please refer to the image that is attached Homework Statement For each of these prisms and cubes (a-f), state whether the surface encloses a: -net positive charge -net negative charge or - a zero net charge Homework Equations The Attempt at a Solution The E-field is...
  10. P

    Find where e-field is 0 question.

    Homework Statement Charge 1 is 8nC and is located at x=-1m. Charge 2 is 12nC and is located at x=3m. Find x where e field is equal to 0 due to the 2 charges.Homework Equations e=kq/(r^2)The Attempt at a Solution The answer is x=1.8, but I just can't seem to get anywhere near that. I know that x...
  11. A

    What is the E-field through the rod?

    Homework Statement What is the electric field within the rod? (See attached document for full question) Homework Equations emf = -d(phi)/dt= integral (E dot dl) The Attempt at a Solution The rod is moving within a uniform magnetic field. There is no change in flux through the...
  12. F

    Gauss's Law with non-uniform E-field

    Homework Statement A long insulating cylinder has radius R, length l, and a non-uniform charge density per volume \rho = e^{ar} where r is the distance from the axis of the cylinder. Find the electric field from the center of the axis for i) r < R ii) r > R The Attempt at a Solution...
  13. A

    Calculating Work and E-field from and equipotential contour graph

    Homework Statement A) Calculate the work performed by an external agent to move a charge of -0.59x10-12 C from `i' to `b'. B) Calculate the magnitude of the electric field at `k' Homework Equations W = q∆V Where ∆V is the potential difference between the two potential lines...
  14. A

    Finding the E-field between two infinite plane charged sheets

    Homework Statement Two infinite-plane non-conducting, thin sheets of uniform surface charge p1 = 13.35 uC/m2 and p2 = -8.65 uC/m2) are parallel to each other and d = 0.245 m apart. (As shown in the diagram below.) What is the electric field between the sheets? (Note: the field is positive if...
  15. A

    Finding the E-field of a mass hanging from a string

    9. [1pt] As shown in the figure above, a ball of mass 0.480 g and positive charge q =32.7microC is suspended on a string of negligible mass in a uniform electric field. We observe that the ball hangs at an angle of theta=15.0o from the vertical. What is the magnitude of the electric field...
  16. B

    Maxwell's Equations: B-field induced from changing E-field

    Homework Statement Parallel plate capacitor with circular plates with radius of 26mm and a plate separation of 6mm. A sinusiodal potential difference is applied across the capacitors plates with Vmax = 170V at a frequency of 60Hz. 170sin(2*pi*60Hz*t) Homework Equations V = ∫E∙dl = El (l...
  17. Q

    Why Does a Dipole in E-Field Point in a Certain Direction?

    does anyone know why the forces point in such a direction? basically, its a dipole (y-orient) in an E-field but why do the forces on the +q and -q slant as such? thanks
  18. F

    Why is E-field 0 outside of this sphere?

    Homework Statement http://img825.imageshack.us/img825/5992/gauss.th.png Uploaded with ImageShack.us 2. Solutions For b) - iv They say the E-field is 0 for r > c Why? Also for part c), they say the answer should be the integral from r = a to r = b. My question is, why...
  19. D

    Find E-field due to an arbitrary finite line of charge at arb point

    Homework Statement Hi everyone. This isn't homework.. I've been out of school for almost a decade; but rather this is for an opengl simulator I'm building. The integrals for the E and B fields of a finite line of moving-charge are well known and can be found in textbooks and online--even on...
  20. G

    Internal E-field of dielectric cylinder immersed in static E-field

    I am having trouble with a homework problem assigned by my physics professor. An infinitely long cylinder of radius a and relative dielectric constant Er is immersed in a static electric field E=Eox where x is supposed to denote a unit vector in the x direction. The cylinder is alligned on the...
  21. F

    How exactly do we know the direction of the E-field here?

    Homework Statement http://plato.stvincent.edu/physics/past/ph112/2008/exam1/s3.pdf How do we know the E-field is radially? And not through the top and bottom?
  22. Y

    E-Field in a Ring: Homework Solutions

    Homework Statement a) What is the E-field at the center of a metal ring which has uniform charge density? b) Is E=0 for any other point within the circumference of the ring?2. The attempt at a solution For (a), since the ring has uniform charge density and is symmetrical, based on symmetry...
  23. Y

    Understanding Conducting Solids: Exploring the E-field Phenomenon

    pardon me for asking such silly question. Why is it that the E-field in the interior of a conducting solid zero? even when the conducting solid have excess positive (or negative) charges? and this conducting solid is placed in an external E-field, will the E-field in the conducting solid...
  24. F

    Help with E-field integral please.

    Hello, I need help solving an integral in the line charge equation for my electrodynamics class. I'm using Griffiths third edition and I understand where the components of the problem come from, but I can't seem to solve the integral, although I'm sure it's very basic. It's been awhile since I...
  25. I

    Why do the Horizontal components cancel in E-Field

    Homework Statement Plane X=0 has a uniform charge density, \rhos while plane X=a has -\rhos. Determine the electric field intensity in region X<0. Homework Equations E=\frac{Q}{4\Pi\epsilon0R2}aR The Attempt at a Solution I already know the answer to this question. What I'm...
  26. L

    D-field -> E-field when the dielectric constant is a function of space

    Hello everyone, I am a little reluctant to post this question because it is a common problem type assigned for introductory electrodynamics courses, so I understand any level of vagueness that should be practiced with regards to answering the question so as to not make it too obvious how to do...
  27. M

    Relativistic Effects on the E-field

    I was trying to read up on the effects of the Lorentz transforms on electromagnetic fields in the stationary and moving frames and came across the following equation for the E-field: [1] E= \frac {Q}{4 \pi \epsilon_0 r^2}* \frac {1- \beta^2}{(1- \beta^2 sin^2 \theta) ^{3/2}} The first...
  28. P

    E-field of a laser pulse and Intensity

    Hi, What is the equation for a E field of a single pulse of a laser? If that laser is shined onto say a grating spectroscope (square law detector), how can I go about deriving an expression for Intensity as a function of frequency at the output of the spectroscope? I know that the square...
  29. N

    Introductory Electromagnetics: induced E-field

    Homework Statement "You have an ideal solenoid with n windings per meter, with a current I = I' sin(wt) going through it. Calculate the induced electric field inside and outside the coil. Side: compare with dipole antenna." Homework Equations Maxwell equations B = n mu I (magnetic...
  30. S

    How Do Point Charges Affect Electric Field Vectors at a Specific Location?

    Homework Statement Point charge q1= -5.00 is at the origin and point charge q2= +3.00 is on the -x axis at x= 3.00 cm. Point P is on the y-axis at y= 4.00 cm . Calculate the electric fields E1 and E2 at point P due to the charges q1 and q2. Express your results in terms of unit vectors...
  31. L

    E-field and H-field in a waveguide

    I find it a bit hard to visualize E field and H field inside a waveguide, specially in modes other than TEM. I know E and H are perpendicular to each other and to the direction of propagation. But I need to see some examples or something like a right hand rule. Basically, I am confused.
  32. K

    Complex amplitude of E-field and phase changes

    Hi, I'm looking through my notes on em waves in dielectrics and the fresnel equations and I've been stuck on this for a while. It states that if the complex amplitude = E0eiΦ is positive there is no phase change. However when the value is negative, the phase change Φ is π.. Why is that...
  33. P

    Understand Hertzian Dipole Antenna E-Field Detachment

    In my electromagnetic engineering class we were talking about Hertzian dipole antennas with an oscillating current source (transmission line) driving the antenna. As part of the description of the behavior as the two ends of the antenna have opposite charges an electric field is created from...
  34. M

    Which direction does the electrical field point in an electrical arc?

    ok, so I've got an arc between two electrodes. What is the direction of the electrical field if there is an electrical field?
  35. S

    Finding the Electric Field in a Coaxial Cable with Volumetric Charge Density

    Homework Statement Consider a coaxial cable that consists of inner/outer conductors of radii a and b, and it is filled with electron cloud with volumetric charge density of ρv = Υ/ρ [C/m3] for a < ρ < b. If outer conductor is +Vo [V] more positive than inner conductor, find E field between...
  36. S

    Distorted orbital shell when E-field applied (Dielectrics)

    Homework Statement Єr = 3.0, atomic density = 1028 atoms/m3. The mag. of the E-field is 10,000 [V/m]. Two electrons in outer orbital shell will distort with an applied E-field. If both both electrons follow some orbital path as a pair, find spacing between center of nucleus and average...
  37. S

    How do I determine the dipole moment from given E-field and point charge?

    Homework Statement E-field at (2[m], 30⁰, 90⁰) is E = 4aѳ [V/m]. Find the magnitude and direction of the dipole moment p. Homework Equations I know that I need I need to solve for the equation: p = Qd, where Q is the point charge at the given point and the distance between +Q and -Q, which...
  38. S

    E-field on a spherical shell with a hole

    A uniformly charged spherical shell with surface charge density \sigma contains a circular hole in its surface. the radius of the hole is small compared with the radius of the sphere. what is the electric field at the center of the hole? I only know this question requires superposition of the...
  39. L

    E-field at various points from two large sheets

    E-field at various points from two "large" sheets 1.You've hung two very large sheets of plastic facing each other with distance d between them, as shown in the figure . By rubbing them with wool and silk, you've managed to give one sheet a uniform surface charge density n1 = -n_o and the other...
  40. L

    Electric Field Between Two Charged Rings: Problem Solved

    1. Two 10-cm-diameter charged rings face each other, 19.0 cm apart. Both rings are charged to + 50.0 nC. What is the electric field strength: At the midpoint between the two rings? At the center of the left ring? 2. E = q/4pi*ep_o*r^2 3. The online problem says this is from a...
  41. T

    Why do the E-field and B-field have different units?

    Note this is more of a coursework theory question then a specific homework question. I am learning about E and B fields and electromagnetic waves. A common EM figure I find is the propagation of a photon where the E and B field propagate through space as seen in the following link...
  42. B

    Frequency and other properties from E-field

    Homework Statement A plane, harmonic, linearly polarized light wave has an electric field intensity given by {E}_z = {E}_0 cos pi*10^{15}*(t - x/.65c) while traveling in a piece of glass. Find (a) The frequency of the light. (b) Its wavelength. (c) The index of refraction of the...
  43. A

    Unravelling Electric Flux: Area Vector and E-Field Vector

    1. When solving for electric flux, we dot product the area vector and the e-field vector. Why does area have a vector, and why is it perpendicular to the surface? Homework Equations phi=EAThe Attempt at a Solution Isn't area scalar; Is it because we just want to simplify the calculations so we...
  44. N

    Griffiths E&M 3.33 write e-field of dipole moment in coordinate free form

    Homework Statement Show that the electric field of a "pure" dipole can be written in the coordinate-free form E_{dip}(r)=\frac{1}{4\pi\epsilon_0}\frac{1}{r^3}[3(\vec p\cdot \hat r)\hat r-\vec p]. Homework Equations Starting from E_{dip}(r)=\frac{p}{4\pi\epsilon_0r^3}(2\cos \hat r+\sin\theta...
  45. E

    Fred's Simple E-field Sensor: Seeking Suggestions

    Hello everyone, My name is Fred and I'm a newcomer to the forum. I'm designing a very simple E-field sensor. So all I did was I got two styrofoam balls, wrapped them around with a few layers of aluminum foil to serve as charge collecting surfaces. Put both "sensors" on the ends of a thin wood...
  46. Y

    What is the antigradient of the given E-field?

    Homework Statement \vec{E}=k(y^2\hat{x}+(2xy+z^2)\hat{y}+2yz\hat{z}) Here k is a constant with the appropriate units. Find the potential, using the origin as you reference point. Check our answer by computing \nabla V. [Hint: You must select a specific path to integrate along. It doesn't...
  47. L

    E-field & electric potential of a metal conductor

    A few questions about electric field here: 1. Why do charges have to be on the outer surface of the conductor? 2. Why no charge on the inner surface of a hollow conductor? 3. If charges cannot be inside the conductor, how come the electric potential is constant throughout the conductor when...
  48. V

    Proof that e-field lines don't cross

    I understand that electric field lines do not cross and a simple explanation is that it violates existence-uniqueness. I'm thinking there is a more complete explanation out there though. I think the answer lies in the realm of dynamical systems and non-linear dynamics, but it's been a whlie...
  49. F

    How Do You Calculate the E-Field of a Semi-Circle with a Uniformly Charged Line?

    A line charge of uniform density \lambda forms a semi-circle of radius R0. Determine the magnitude and direction of the electric field intensity at the center of the semi-circle. I won't bother with uploading a picture I'm pretty sure you can picture this without. My trouble with this is I'm...
  50. E

    E-Field over Uniformly Charged Disc

    Homework Statement http://scitec.uwichill.edu.bb/cmp/online/P10D/Hunte/Electric%20fields_files/image122.jpg Find the Electric Field at Point P at height z over a uniformly charged disc of radius a with uniform charge Q. Homework Equations The Attempt at a Solution I'm looking...
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