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. JD_PM

    Average electric field over a spherical surface

    Homework Statement I was working out problem 4, chapter 3 of Introduction to Electrodynamics by Griffiths: a) Show that the average electric field over a spherical surface, due to charges outside the sphere, is the same as the field at the centre. b) What is the average due to charges inside...
  2. A

    -qEx for a vertical spring in a constant Electric field

    A massless spring of spring constant k = 13 Newtons per meter hangs purely vertically. A 20 Newton, 5(10-3) Coulombs charged particle is attached to the spring and released from rest. Besides all this, there is also a constant, external Electric Field of 9000 Newtons per Coulomb pointing...
  3. Q

    Maximum Horizontal Force of Relativistic Point Charge

    Homework Statement A charge q1 is at rest at the origin, and a charge q2 moves with speed βc in the x-direction, along the line z = b. For what angle θ shown in the figure will the horizontal component of the force on q1 be maximum? What is θ in the β ≈ 1 and β ≈ 0 limits? (see image) Homework...
  4. Taxi1337

    Sphere-with-non-uniform-charge-density ρ= k/r

    I am working on the same problem as a previous post, but he already marked it as answered and did not post a solution. https://www.physicsforums.com/threads/sphere-with-non-uniform-charge-density.938117/ I am curious as to a method of finding the ##k## and substituting into the electric...
  5. L

    What Is the Magnitude of the Electric Field Between Parallel Plates?

    Homework Statement An electron is projected with an initial speed v0 = 4.65×106 m/s into the uniform field between the parallel plates in (Figure 1). The direction of the field is vertically downward, and the field is zero except in the space between the two plates. The electron enters the...
  6. D

    Dependence of an electric field on distance

    Homework Statement A proton located several proton diameters away from a small charged object carrying charge q is subject to an electric field of magnitude E. As the proton moves a distance d along the x-axis away from the object, the electric field magnitude drops to E/4. If the charged...
  7. martinbandung

    Calculating Electric Field at Point A from Uniformly Charged Arc

    Homework Statement Find electric field at Point A its an arc with uniform density= lamda https://drive.google.com/file/d/14cBqE2dMe_w0nb9LtPG0h1cUOrzGWt6g/view?usp=sharing the problem Homework Equations E=intergal dq/r^2 The Attempt at a Solution I've tried using wolfram and cosine rule to...
  8. Zack K

    Final potential difference of a 2 capacitor system

    Homework Statement An isolated parallel-plate capacitor of area ##A_1## with an air gap of length ##s_1## is charged up to a potential difference ##\Delta V_1## A second parallel-plate capacitor, initially uncharged, has an area ##A_2## and a gap of length ##s_2## filled with plastic whose...
  9. Zack K

    Potential at center of sphere of radius R and charge -Q

    Homework Statement What is the potential at the center of the sphere relative to infinity? The sphere is dielectric with uniform - charge on the surface of the sphere. Homework Equations ##k=\frac {1}{4\pi\epsilon_0}## ##V=\frac {KQ}{r}## The Attempt at a Solution If the distance r=0 it would...
  10. J

    Batteries and the electric field inside a wire

    I have a question what does create a electric filed inside coducting wire? And is it the same field trought the whole wire? Thanx for answers.
  11. Mutatis

    Find the electric field at an arbitrary point

    Homework Statement A distribution of charge with spherical symmetry has volumetric density given by: $$ \rho(r) = \rho_0 e^{ \frac {-r} {a} }, \left( 0 \leq r < \infty \right); $$ where ##\rho_0## and ##a## is constant. a) Find the total charge b) Find ##\vec E## in an arbitrary point...
  12. ino

    Find the electric field at the point P on a right triangle

    Homework Statement https://www.physicsforums.com/threads/find-the-electric-field-in-the-point-p-of-a-right-triangle.965285/#post-6125768 knowing that the three charges are equal and that the angles of the triangle are 90°, 45°, 45°. Homework Equations The Attempt at a Solution I tried...
  13. L

    Flux Through a Cube's Face with our Point Charge at a Corner

    Homework Statement A charge q is placed at one corner of a cube. What is the value of the flux of the charge's electric field through one of its faces? Homework Equations The flux surface integral of an electric field is equal to the value of the charge enclosed divided by the epsilon_naught...
  14. Zack K

    What Is the Electric Field of a Curved Rod at the Origin?

    Homework Statement A rod of charged -Q is curved from the x-axis to angle ##\alpha##. The rod is a distance R from the origin (I will have a picture uploaded). What is the electric field of the charge in terms of it's x and y components at the origin? k is ##\frac {1} {4\pi \epsilon_0}##...
  15. S

    Electric field at a point problem

    Homework Statement In the figure above, charge A is -5.00 nC, charge B is 10.0 nC, and charge C is 5.00 nC. If x = 2.10 cm and y = 4.20 cm, what is the electric field at the dot? Homework Equations E = kq/r^2 The Attempt at a Solution r = distance from A to point = sqrt(x^2+y^2) Ea = kq/r^2...
  16. J

    Theoretical models of the Earth's Electric Field?

    I am doing some research into atmospheric energy harvesting. To design a proper feasibility experiment, I need to establish some theoretical baselines. I see a lot of values for the field strength for example, tossed about from various papers. However, there does not seem to be a standard...
  17. C

    Find the electric field of a point outside sphere

    Homework Statement Find the electric field of a point outside sphere without using Gauss's law. (Do not evaluate the integral) Homework Equations Coulomb's Law Spherical Co-ordinate System The Attempt at a Solution I have attached my attempt as a picture but now I am stuck, I don't know how I...
  18. C

    Exploring Electrostatics with Gauss Theorem

    Having come experimentally to an interesting electrostatic effect, I have returned, aged 47, to my old books in physics. It turns out that my books delight in using Gauss theorem etc. in rather ideal geometrical surface charge distribution, but never gave me the tools to answer to this simple...
  19. Zack K

    Change in the Electric Field Due to a Copper Wire Being Inserted

    Homework Statement A point charge of 6 × 10−9 C is located at the origin. The magnitude magnitude at ##\langle 0.6,0,0\rangle## m is 150 N/C Next, a short, straight, thin copper wire 5 mm long is placed along the x axis with its center at location ##\langle 0.3,0,0 \rangle## m. What is the...
  20. Zack K

    Approximating the force on a dipole Taylor series

    Homework Statement Show that the magnitude of the net force exerted on one dipole by the other dipole is given approximately by:$$F_{net}≈\frac {6q^2s^2k} {r^4}$$ for ##r\gg s##, where r is the distance from one dipole to the other dipole, s is the distance across one dipole. (Both dipoles are...
  21. PainterGuy

    Electric field outside a parallel plate capacitor

    Hi! Could you please help me with the queries below? Thanks a lot. Question 1: My question is about the field outside the plates of parallel plate capacitor. It is said that the field(s) between positively and negatively charged plates gets added up but the field(s) outside the plates gets...
  22. Zack K

    Distance of a Point Charge: Solving for Initial Distance Using Relativity

    Homework Statement You make repeated measurements of the electric field ##\vec E## due to a distant charge, and you find it is constant in magnitude and direction. At time ##t=0## your partner moves the charge. The electric field doesn't change for a while, but at time ##t=24## ns you observe a...
  23. Zack K

    Magnitude of an Electric Field due to a dipole

    Homework Statement A dipole is located at the origin, and is composed of charged particles with charge +e and -e, separated by a distance 2x10-10m along the x-axis. Calculate the magnitude of the electric field due to the dipole at location ##\langle 0.2\times 10^{-8}, 0, 0\rangle##m Homework...
  24. Zack K

    Location of charged particle given magnitude of position

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  25. I

    Model electron movement in an electric field (Magic Eye tube)

    Hello there, I'd like to model a simplified version of a "Magic Eye" tube (e.g. without the amplification triode, and for a start, 2 dimensions only), or the visible display behavior. What I'm talking about: https://en.wikipedia.org/wiki/Magic_eye_tube#Operation Here is a nicer depiction of...
  26. H

    Calculate Net Electric Field at Point P | Two Charges 42cm Apart

    Homework Statement Two charges, one of 3.2 x 10 ^ -9 C, the other one of -6.4x10^-9 C are 42 cm apart. Calculate the net electric field at point P, 15 cm from the postie charge, on the line connecting the charges (+) -------------(Point)---------------------- (-) 15cm...
  27. Shivang kohlii

    Amplitude of a mass joined to a spring in the presence of an E-field

    Homework Statement A block of mass m having charge q placed on smooth horizontal table and is connected to a wall thorough an unstretched spring of constant k . A horizontal electric field E parallel to spring is switched on. Find the ampliture of the shm by the block. Homework Equations kx=...
  28. Haddon

    Calculating the magnitude of an electric field

    Homework Statement An electron enters the lower left side of a parallel plate capacitor and exits precisely at the upper right side (just clearing the upper plate). The initial velocity of the electron is 7*10^6m/s parallel to the plates. The capacitor is 2cm long and its plates are separated...
  29. T

    Electric field of a non-conducting sphere

    Homework Statement A solid non-conducting sphere of radius R carries a uniform charge density. At a radial distance r1= R/4 the electric field has a magnitude Eo. What is the magnitude of the electric field at a radial distance r2=2R? Homework Equations Gauss's Law: ∫EdA=Qencl / ε0 Charge...
  30. A

    Time-varying electric field measurement using dipole

    Hello, I am trying to measure the time-varying electric field of a parallel plate capacitor using short dipole antenna, but my numbers are off by almost 100 times. I have a parallel plate capacitor, A=23cmx11cm, d=10cm. I apply 10sin(2pi*1KHz) and 10sin((2pi*1KHz)+180deg) to each plate. I am...
  31. N

    Why is there a voltage drop in a metal with no electric field present?

    Metals are highly effective at screening electric fields. If we place two contacts reasonably far away from each other on a piece of metal and apply a voltage bias, the charge carriers in the section that is far enough from both the contacts should be unaffected by the electric field. Why then...
  32. H

    Calculating the final velocity of a simple electric train

    I am currently in grade 12, and for a physics project (a huge project, which gets assigned to you at the start of the semester and needs to be completed just before exams. You think up your project, make a proposal for it and you prove your hypothesis to be right after a presentation and lab...
  33. Adesh

    How to prove that electric field propagates like a wave?

    I was studying Feynman Lectures on Physics Volume 1 chapter 29. In there he proves that electric field propagates like a wave. Here is my attempt (in image), please tell me my mistake. Thank you
  34. H

    Voltage and electric field in capacitor

    1. We've been given a spherical capacitor with radius of 1 cm for inside electrode and 2 cm for outside electrode. Voltage between electrodes is 360 V and the task is to find largest and smalles electric field strength in capacitor.2. I'm not sure how voltage given in capacitor works and how to...
  35. P

    Wire surrounded by a linear dielectric in a uniform E field

    Homework Statement We have an uncharged, conducting wire with radius a. We surround it by a linear dielectric material, εr, which goes out to radius b. We place this in an external electric field, Eo. Homework Equations We have electric potential inside (a < s < b) Vinbetween=Acosφ +...
  36. Clara Chung

    Metal sphere in an electric field

    Homework Statement The question is exactly the same as this question https://physics.stackexchange.com/questions/250297/metal-sphere-in-a-uniform-electric-field However, it says "Then by symmetry the entire xy plane is at potential zero" in the book. I don't understand this. Homework...
  37. Ivan Hu

    Electric Field due to dipole - solution check

    Homework Statement Hi guys, my exam is in four days and my tutor for the electromagnetic module is neither very active nor very competent, so I would like you guys to check my solution for this question. I am afraid I might have messed up some signs or some linear algebra. Homework Equations...
  38. G

    Ratio of the Electric field to the Magnetic field

    Dear all. I would like to know the general expression of the ratio of the electric field strength E to the magnetic flux density B. I know E/B = c, where c is the speed of light, for a vacuum, but I want to know if this is stil valid for any material where the electric and magnetic fields are...
  39. thariya

    A Quantization of the electric field inside a box

    Hello all, The second quantization of a general electromagnetic field assumes the energy density integration to be performed inside a box in 3D space. Someone mentioned to me recently that the physical significance of the actual volume used is that it should be chosen based on the detector used...
  40. Akash47

    What is the Electric Field at a Point Surrounded by Infinite Charged Particles?

    There are infinite number of charges each with charge q along a straight line at a distance of 1,2,4,8,16,… … … unit from a point. What is the electric field at this point? No idea about it.Please help me out.
  41. G

    Net Electric field due to 3 charges

    Homework Statement There is a 3nC charge at (-3,0), -6nC at (0,2) and 5nC at (1,0). What is the electric field at the origin (0,0)? Homework Equations ##E = \frac{Q}{4 \pi \epsilon_0 r^2}## The Attempt at a Solution i think its ##(\frac{1}{4 \pi \epsilon_0})(-\frac{14}{3} i - \frac{3}{2} j)##...
  42. B

    Dipole problem with electric fields

    Dipole problem (which is solved through mirror imaging) has been troubling me with its solution. I understand everything except how the dipole moment's coordinates came to be, since when converted into x-y axis, its doesn't make sense. (problem 4.6) The screenshot contains the solution which...
  43. B

    Electric field of "half" an infinite charged sheet

    Homework Statement A charged sheet with charge density ##\sigma## is described by ##-\infty<x<0,-\infty<y<\infty, z = 0##. Find the electric field at ##(0,0,z)##. Homework Equations Electric field of continuous density charged body from the Coulomb law: $$E = \frac{1}{4\pi...
  44. B

    Calculating the Electric Field outside a dielectric

    In the textbook (Introduction to Electrodynamics by Griffiths), the problem in the attached image asks to find the electric field ##E## outside a dielectric. The problem consists of dividing the electric field into the one produced by the negative charges in the dielectric and another by the...
  45. B

    Electric Field and Potential in a conductor

    So in my textbook (Introduction to Electrodynamics by Griffiths) it said that inside a conductor, the electric field E would have to zero, since if it wasn't the free charges would move accordingly and create a electric field that cancels the original field. But in a question that soon followed...
  46. archaic

    Force of one distribution of charge on another

    Homework Statement I need help on solving this exercise : We have a ring of radius = ##a## uniformly charged (total charge = ##Q##) and on its axis a segment ##OA## (length = ##a## also) of uniformly distributed positive electric charges with the charge density ##\lambda'## and of total charge...
  47. YMMMA

    What causes electric field/ magnetic field?

    Homework Statement What causes electric field? What causes magnetic field? (I) stationary electric fields (II) moving electric charges (III) a changing magnetic field IV) a current-carrying wire Homework Equations E=F/q B=μI/2πr E electric field F elecric force Q charge B magnetic field I...
  48. Silentwhale

    Electricity and magnetism: Electric Field for Two Long Charged Lines

    Homework Statement Given two very long lines each is charged with linear density +lambda Coulombs/meter. The two lines are separated by a distance of d metres. A) show the electric field E, at any point along one of the lines due to the other line is E = lambda/(2 (pi)(epsolon o)(d)) (Note...
  49. J

    Design a Handheld Electric Field Meter with Arduino

    Hello, I want to create a handheld electric field meter to measure the strength at a certain point with an arduino. I have seen various ideas online but I am still not sure what kind of design to use. Is the right concept to use two antennas. Measure the voltage on each and then calculate the...
  50. YMMMA

    Where is the electric field greatest in magnitude?

    Homework Statement In the file Homework Equations No equations needed The Attempt at a Solution I answered it C. Since I learned that at the tip there are most of the charges. Therefore, it’s the point of the greatest E field magnitude. But another tutor told me that it is a circle, and...
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