What is Electric fields: Definition and 506 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. G

    Conductors in large electric fields

    You place a conductor in an electric field. The charges inside the conductor will relocate, to form an opposing electric field which cancels the outside field, making the field inside the conductor zero. However, surely there's a limit to how big an opposing field the charges in the...
  2. I

    Quick question about electric fields in capacitors.

    Homework Statement At which location will the electric field between the two parallel plates of a charged capacitor be the strongest in magnitude? a. near the positive plate b. near the negative plate c. midway between the two plates at their ends d. midway between the two plates nearest...
  3. F

    Electric fields through parallelepiped

    I have taken my Gauss surface as the front of the shape, with E_1 coming through uniformly. I get the right answer for the charge inside the shape, but I'm unsure about b. I imagine a situation that I've drawn could be possible, but I've never seen it before, so I do not know. I'm thinking that...
  4. E

    Gauss's Law and Electric fields

    It is asked to find the electric flux through a "gaussian" sphere which has a point charge (-3 microcoloumbs) enclosed with the radius of 0.2 m ... I can shortcut this and use Flux= q Enclosed / e0.. However, i want the other approach using the formula Flux = ∫ E da... I know that E is constant...
  5. B

    Electric Fields Cancelling Out?

    Homework Statement An example problem I am reading is about the electric field of a uniform ring of charge. I attached the diagram provided in the problem. What confuses me is that the electric field lines in the y-direction cancel out. Wouldn't the fields have to cross, if they were to...
  6. S

    Magnitude and Direction of Electric Fields

    Hey yall. This is a question from my homework but it's so basic that it's just to help with the concept for me. So the question is this: A small object A, electrically charged, creates an electric field. At a point P located 0.250 directly north of A, the field has a value of 40.0 directed to...
  7. M

    Two problems on Electric Fields and Electric Potential

    Homework Statement 1st Problem (a) Consider the electric potential V = C . r, where C is a constant vector. Find the electric field E(r). (b) For a given uniform electric field E = E(0)z^, using part (a) find the electric potential for this electric field...
  8. M

    Attempting to find tension force with electric fields

    Homework Statement A small conducting sphere of mass 5.0x10^-3 kg attached to a string of length 20 cm, is at rest in a uniform electric field E. There is a charge of -5.0x10^-6 coulomb on the sphere. The string makes an angle of 30° with the vertical. Calculate the tension in the string...
  9. V

    Total energy stored in the electric fields, exess energy

    Homework Statement one capacitor is charged until its stored energy is 4.0 J, the charging battery then being removed. a second uncharged capacitor is then connected to it in parallel. if the charge distributes equally what is now the total energy stored in the electric fields? where the...
  10. J

    Electric Fields and excess charge vs charge

    Hello, I have a few questions (with regards to conducting hollow spheres) . 1: What is the difference between a charge in the sphere and an excess charge coming out of the sphere or the charge resting on the outside of a sphere? 2: Image a conducting sphere that has a shell of a small...
  11. B

    Where Do Electric Fields Cancel Out Between Two Charged Particles?

    Homework Statement In the figure below, determine the point (other than infinity) at which the electric field is zero. (Let q1 = -2.45 µC and q2 = 6.50 µC.) Homework Equations The Attempt at a Solution Here is a little commentary my author gives on this problem: Each...
  12. R

    What instruments did gauss use to measure flux / electric fields?

    Gauss equations state that the flux of a gaussian surface is equal to the sum of all the electric field times the surface area. Although he stated this in theory, how was he able to prove it possible. What measuring device do people use to prove that this theory is correct?
  13. Q

    Particle motion + electric fields

    Homework Statement see attachment for question wording. a) find acceleration b) find horizontal displacement c) find final velocity vx=4.0*10^6m/s ε=4.0*10^2 N/C Δdy=0.02m mass of electron = me = 9.11*10^-31kg charge of electron = qe = -1.6*10^-19 C Homework Equations suvat...
  14. N

    How do you find the electric fields of regions between parallel infinite sheets.

    Homework Statement How do you find the electric fields of regions between parallel infinite sheets of charge? The set up: 3 parallel infinite sheets of charge a,b,c from left to right. Region 1 is to the left sheet a. Region 2 is between sheets a and b. Region 3 is between sheets b and c...
  15. D

    Uniform Electric Fields: Understanding Coulomb's Law and Field Intensity

    Coulomb's Law F = kqq/r^2 Why does the intensity of a uniform electric field not get weaker in the middle? I would understand this if the intensity over distance was a linear function, but it isn't. The force near one of the plates would approach infinity, because r^2 is so small... but in...
  16. mishima

    Impossible electric fields examples?

    I was trying to think of more impossible electric fields than my book has. I understand it is anything that breaks the rule that the path integral is zero. One example is a circular field. I was trying to picture some more complicated 3d examples. Are all magnetic fields an impossible...
  17. M

    Electric fields in an Inductor

    En and Ec are the non-conservative and conservative electric field respectively. I've quoted this from the textbook I'm using (University Physics by Young and Freedman 12th edition). Now, it seems to me that the author just invoked the assumption that the inductor have negligible resistance...
  18. H

    Feynman: Relativity of Magnetic and Electric Fields

    The diagrams aren't coming through on my system, but the text is readable: http://books.google.com/books?id=hlRhwGK40fgC&pg=SA13-PA6&lpg=SA13-PA6&#v=onepage&q&f=false First off, I'm pretty sure he re-uses ##\rho_\omicron## to mean different things at different points in the discussion...
  19. N

    Electric fields and gravitational fields

    Homework Statement for electric fields i know total flux through a closed surface is proportional to tot. charge enclosed..goes ssame for gravt. fields. total gravitational flux through a closed surface is proportional to total mass enclosed. Now there's the next equation that says if a...
  20. nukeman

    General questions about Electric fields and how to manipulate/produce them.

    If my question is lacking something in terms of its validity, please let me know (I am not too seasoned in electric fields) :) Here is the source of my question: http://phys.org/news198350025.html Ok... The brain produces it own electric field, by firing neurons and the chemicals that produce...
  21. M

    Exploring Electric Fields from a Charge Distribution

    1. Homework Statement [/b] Positive charge Q is distributed uniformly along the x-axis from x=0 to x=a. A positive point charge q is located on the positive x-axis at x=a+r , a distance to the right of the end of Q. Observe the figure below My goal is to try to explain the...
  22. N

    Point Charges, Maginitudes and Electric Fields.

    Homework Statement Point charge 2.5 microC is located at x = 0, y = 0.30 m, point charge -2.5 microC is located at x = 0 y = -0.30 m. What are (a)the magnitude and (b)direction of the total electric force that these charges exert on a third point charge Q = 4.5 microC at x = 0.40 m, y = 0...
  23. C

    Electric Field at the Center of a Square with Four Charges

    Homework Statement What is the electric field in the middle of the square in magnitude and direction? four charges are arranged at the outer corners of the square in order from left to right , then top top to bottom respectively +q,-2q,-q,+2q.Homework Equations The Attempt at a Solution...
  24. A

    Quantam Vacuum - Strong Electric fields.

    Hello, I am not yet well-versed in quantum theory of the vacuum, but I certainly have encountered it everywhere I have turned in my studies. Since my electron paper is unwieldy I want to run by folks my thoughts of percolations in the vacuum. So many people have spoken of "electrons and...
  25. K

    Electric Fields and Protons: Solving for Time, Velocity, and Distance

    Homework Statement Two protons that has a 'm' mass and '+q' charge appears suddenly at the time t=0 as the picture shows. The distance from A to B is 'd0'. They start there motion from 0 velocity and move towards B. 1. What are the t1 and t2 times that are taken by the two masses to get to...
  26. E

    Are the directions of electric fields lines affected by Gravity?

    I recall that the path of light itself can be altered by gravity, then, being part of the electromagnetic force, then is it safe to assume that the paths of electric fields lines can also be warped? I would imagine that the consequences would be enormous for electric flux in curved space...
  27. R

    Detecting induced electric fields in the ocean

    Hi everyone: Since there are many ions in ocean water, and these ions are carried by ocean currents, and they are moving through the Earth's magnetic field, by the electromagnetic induction laws, wouldn't there be a induced electric field in the ocean? if i want to detect this electric field...
  28. W

    Finding magnitude of new electric fields

    Homework Statement In Fig. 22-31 the four particles are fixed in place and have charges q1 = q2 = 3e, q3 = 2e, and q4 = -10e. Distance d = 5.42 μm. What is the magnitude of the net electric field at point P due to the particles? Homework Equations E=1/(4πε0) x [ q4/2d^2-q3/d^2] j...
  29. G

    Solving for Magnetic Fields from time varying Electric fields

    Hi all, new to the forums. Anyways I had a day off and decided to try something quirky with maxwells equations. Using the Ampere-Maxwell equation, I tried to solve for the magnetic field that would be created by a <0,0,t> Electric field. (No current and no magnetic materials) ∇ x B = εμ(∂E/∂t)...
  30. S

    Electric Fields , Finding final velocity. NEED HELP

    Homework Statement Mass= 15g Q1= 8.0uC Q2= 25 uC (stationary) Q1 is released from a point 12cm from Q2. How fast will Q1 be moving when the separation is 20cm. Homework Equations F=ma F=qe F=kQq/r2 E=kQ/r2 Ke=mv2/2 W=FD vf2=vi2+2ad The Attempt at a Solution...
  31. N

    Why Do Electric Field Lines Never Cross?

    (1)Which of the following statements about electric field lines is false? a) They are perpendicular to the surface of an isolated conductor b) They never intersect c) They indicate the path along which a test charge moves d) More indicate a stronger field e) They can be either straight or...
  32. S

    Does electric field obey superposition?

    Does electric field vary with distance? For example, When I fix an electron along an axis and then fix another electron let's say 5m along the x-axis from the first, the first electron has an electric field that is creating a force on the other electron. If I free the second electron to move...
  33. S

    Spherical capacitor and electric fields

    A spherical capacitor contains: Region1: solid spherical conductor (radius=0.5mm, Q=7.4 micro coulombs) Region2: surrounded by a dielectric material (er=1.8, radius extends to 1.2mm, Region3: outer spherical non-conducting shell (variable charge per unit volume p = 5r, outer radius=2.0 mm)...
  34. L

    Capacitors & Electric Fields and how they change relative to each other

    1. I have a capacitor that has been fully charged with a 10v source, then that source is removed. If I increase the distance between the plates, does the electric field stay the same, and the voltage increase, or does the voltage stay the same, and the field decrease? Or is it something that...
  35. T

    Physics Faraday's Law and Induced Electric Fields

    Homework Statement A wire loop with area 8.00 cm2 is placed inside a 20.0 cm long solenoid with 5.00×10^4 turns that carries a current of 1.10 A. The loop is concentric with the solenoid. If the length of the solenoid is stretched so that its length increases at a rate of 8.000e-2 m/s, with...
  36. D

    Question on capacitance and electric fields

    Consider a thin parallel plate capacitor of an area of of 2.0x10^-4 metres squared, with a thickness of 1.2x10^-4 metres. The top and bottom thirds of the capacitor are filled with a dielectric material with a relative dielectric permittivity εr1=4, and the central third, with another material...
  37. F

    How Do Charge Distributions Affect Electric Fields in Capacitors?

    Homework Statement Consider a capacitor that consists of two metal plates of nonzero thickness separated by a positive distance d. When such a capacitor is connected across the terminals of a battery with emf EMF, two things happen simultaneously: Charge flows from one plate to another, and a...
  38. B

    Electric Fields and point charges

    Homework Statement A point charge −3 pC is concentric with two spherical conducting thick shells, as show in the figure below. The smaller spherical conducting shell has a net charge of 22 pC and the larger spherical conducting shell has a net charge of 18 pC. 1-4)Answer in units of...
  39. M

    Max Charge on Sphere: Calculating with Electric Fields

    Homework Statement An empty, hollow, spherical conductor with radius R = 20 cm is supported in air. Electrical breakdown occurs when the electric field at the conducting surface exceeds 3.0 × 106 V m−1. What is the maximum charge that can be placed on the sphere? Homework Equations F = k...
  40. K

    Finding Expressions for Electric Fields with Radius

    Homework Statement A solid nonconducting sphere of radius a has a has a total charge +Q uniformly distributed throughout its volume. The surface of the sphere is coated witha avery thing (negligable thickness) conducting layer of gold. A total charge of -2Q is placed on this conducting layer...
  41. O

    Advanced physics problems on electric fields.

    Homework Statement Secret Agent Jane Pond is testing out a new particle ray gun. She knows the particles in the ray have charge -2e and a mass of 50u. (u = atomic mass unit.) To determine the speed of the particles in the ray, Jane needs a region of uniform electric field. She takes...
  42. C

    Four Equidistant Particles in electric fields

    Homework Statement In Fig.22-30, the four particles form a square of edge length a = 6.50 cm and have charges q1 = 7.59 nC, q2 = -10.9 nC, q3 = 11.5 nC, and q4 = -6.06 nC. What is the magnitude of the net electric field produced by the particles at the square's center...
  43. R

    Where Should a Proton be Placed to Create an Electric Field at the Origin?

    Homework Statement You want to create an electric field = < 0, 3x10^4,0 > N/C at location < 0, 0, 0>. Where would you place a proton to produce this field at the origin? Homework Equations 1/4?? * q/r^2 = 3x10^4 N/C (if you can't see the 1/4th part of the equation it's...
  44. L

    Electric Fields in Equilateral Triangle

    Homework Statement A point charge q = +2.0 µC is placed at each corner of an equilateral triangle with sides 0.23 m in length. What is the magnitude of the electric field at the midpoint of any of the three sides of the triangle? 3. I want to know if I did this correctly, or totally...
  45. C

    Electron velocity in Electric Fields

    Homework Statement An electron with a speed of 5.57 × 108 cm/s in the positive direction of an x-axis enters an electric field of magnitude 2.72 × 103 N/C, traveling along a field line in the direction that retards its motion. (a) How far will the electron travel in the field before stopping...
  46. rhody

    Medical Bill Doyle: Treating cancer with electric fields

    TED Video: Treating cancer with electric fields I found it amazing that patients wearing the radio therapy patches were able to carry on with their daily lives and without the dangerous debilitating side effects associated with chemo and radiation. Pretty interesting watching cell division...
  47. P

    Electric Fields using Gauss' law

    Homework Statement http://i.minus.com/jbxXiQZmmiOQtS.png Homework Equations Elecric flux = Integral of closed surface of E dotted into dA = qenclosed / ε0 Rho = 50 x 10^-6 abs(z) The Attempt at a Solution Integral of closed surface of E dotted into dA will end up being EA when E is...
  48. M

    How Does Charge Distribution Affect Electric Field Inside a Hollow Sphere?

    Homework Statement A total charge Q is spread uniformly over the surface of one hemisphere of a hollow insulating spherical hull of radius R. The magnitude of the electric field at the centre of the ball(point C) will be? The Attempt at a Solution The answer was less then that KeQ/R^2, was...
  49. M

    Effect of radius changes on electric fields and potential difference?

    Hello! Okay so I understand that electric potential: V = kQ/r ...must be influenced by the radius doubling because it would make the potential energy half of what it originally was because of the proportionality law, v is proportional to 1/r. With electric fields though, how can...
  50. O

    Charges, Electric Fields, and Work?

    Homework Statement a +70µC charge is placed 50 cm from a -50µC charge. How much work would be required to move a -.5µC test charge from a point 10 cm from the +70µC charge to a point 20 cm from the -50µC charge? Homework Equations F=k(q_{1}q_{2}/r^{2}) PE=Fd ...that's all I could get...
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