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. D

    I Charged black hole - static electric field lines

    Where do the static electric field lines appear to originate from a charged black hole, non rotating, Reissner–Nordström metric? I've had a number of qualified physicists say they appear to come from the center of the black hole, but people on these forums have said that doesn't make sense...
  2. Benjamin

    Calculating Electric Field from Force on a Point Charge

    Homework Statement What is the electric field at a point when the force on a 1.20 µC charge placed at that point is = (3.0 î -5.0 ĵ) × 10-3 N? Homework Equations E = KQ/d^2 The Attempt at a Solution I'm having trouble visualizing the question. I attempted to draw it out, but its not making...
  3. G

    What is the Simplified Equation for a Uniform Electric Field?

    Homework Statement [/IMG] Homework Equations See Below The Attempt at a Solution Maybe my answer is right but not simplified enough. But if it is I am having trouble seeing the mathematical equivalency. Please help. Thanks in advance!
  4. Matt Chu

    Angle of escaping electric field lines

    Homework Statement Two charges 2q and -q are located at x = 0 and x = a respectively. There are field lines extending from the positive charge and lines going inwards to the negative charge. Some of these lines go from the positive charge to the negative, but some go off to infinity from the...
  5. Brystephor

    Electric field magnitude between two charged disks problem

    Homework Statement Consider two thin disks, of negligible thickness, of radius R oriented perpendicular to the x axis such that the x axis runs through the center of each disk. (Figure 1) The disk centered at x=0 has positive charge density η, and the disk centered at x=a has negative charge...
  6. Likith D

    Gauss' law for uniformly charged space

    the problem: Say we have the entire space uniformly charged. Then, the E field experienced by any point is zero, from symmetry.* But, it means that for any Gaussian surface, the flux though it is zero even though the charge enclosed is clearly not. Gauss' law seems to disagree with symmetry, but...
  7. M

    How Do You Calculate Electric Field Strength and Direction?

    Homework Statement The diagram is attached. What is the strength of the electric field at the position indicated by the dot in Figure 1? What is the direction of the electric field at the position? Specify the direction as an angle measured clockwise from the positive x axis. Homework...
  8. M

    Electric field vector in component form

    Homework Statement A -12nC charge is located at (x,y) = (1.0cm, 0cm). What are the electric fields at the positions (x,y) = (5.0cm, 0cm), (-5.0cm, 0cm), and (0cm, 5.0cm)? Write each electric field vector in component form. Homework Equations E=k(q/r2) The Attempt at a Solution I was able to...
  9. starstruck_

    Calculating voltage within and outside of a solid sphere

    Homework Statement A solid sphere with radius R=12 m has charge Q=3 nC distributed uniformly throughout its volume. (a) Calculate the potential difference between a location at infinity and a location on the sphere’s surface. (b) Calculate the potential difference between a location on the...
  10. L

    Finding the electric field between two parallel plates

    Homework Statement Hi everyone! This is the homework problem I'm struggling with! Initial velocity = 107 meters per second The particle is an electron, so: Charge = -1.6 x 10-19 coulombs Mass = 9.11 x 10-31 kilograms Homework Equations Kinematic formula x = vot + 1/2 at2 Newton's law...
  11. lawsonfurther

    Can there be an electric field inside an insulator?

    Just as the title asks, I wonder if there can be any electric field inside an insulator when a point change is placed near it. If so, why?
  12. S

    Find the electric field at the point 20cm above the centre

    Homework Statement Hi guys, I was hoping I could get some help on this question! The question: "Find the electric field at the point 20 cm above the center of the square made of 4 charged rods of L = 20cm and Q=1mc each. Homework Equations I believe E = (KQ)/r^2 is the only equation needed...
  13. starstruck_

    Calculating electric field strength

    Homework Statement A cylinder of radius R= cm 1.2 and length L= 51 cm has a charge Q=2.3 μC spread uniformly along its surface (and not on its flat ends). a) Calculate the electric field strength a distance d=4 mm from the cylinder’s surface (not near either end) b)Calculate the electric...
  14. ubergewehr273

    I Divergence of ##\frac {1} {r^2} \hat r##

    Basically a case where a positive charge q is placed in space which for convenience is taken as the origin. This electric field must have a large positive divergence but yet when evaluated mathematically we get 0. Also when we find divergence, we find it for a point right ? or is it possible to...
  15. R

    Electric field at the surface of a spherical shell?

    What is the value of electric field at the surface of a spherical shell?
  16. C

    Electric field between two cylinders in a vial

    Homework Statement Hello everyone, I am writing here regarding a doubt I have about electric fields. Our set up consists on two rod shape electrodes in a cylindrical glass vessel separated by 6 mm from each other, with one of the electrodes grounded (electrodes dimensions: 0.5 mm diameter and...
  17. F

    Which creates an electric field -- charge or a charged particle?

    wich creates an electric field charge or a charged particle (electron)
  18. F

    The difference between electric field and electrical charge

    what is difference between electric field and electrical charge?
  19. lawsonfurther

    Electric Field Lines: Midpoint Between 2 Charges

    I notice from the classic electric field line diagram of two positive charges that there is no field line going along the line segment joining those two charges. So I wonder whether that is true or it's just a way that you can't show all the field lines in the diagram but it actually exists. (I...
  20. B

    Electric field in a capacitor with multiple dielectrics

    Hi, I am trying to understand capacitors and have come across the example in the attached image. What I would like to understand is how to calculate the electric field at some distance x within the capacitor. With x>>R , x<R and x=R . The image is of two circular disks as the...
  21. C

    Can an axisymmetric electric field be created without charges?

    That is, a field that accelerates charges in opposite directions on each side of an axis. I was thinking about interference of similarly polarized waves traveling in opposite directions (so that electric field peaks and valleys overlap but magnetic field adds constructively) - would there be an...
  22. H

    Can We Create an Electric Field Blocking Material Like Mu-Metal?

    Is it possible to create a material that will block an electric field like mu-metal blocks magnetic fields?
  23. Pushoam

    What is the relationship between induced emf and induced electric field?

    Homework Statement Homework EquationsThe Attempt at a SolutionThe emf gets induced due to the changing flux. The flux through the rod remains 0. So, there is no induced emf. I don’t know how to calculate induced electric field. But as there is no induced emf, so there is no induced...
  24. J

    Electric field intensity at a distance

    Homework Statement Homework EquationsThe Attempt at a Solution The radiations from the bulb spread radially outwards such that "Power at a distance r" = Power radiated/4πr2 . If distance is unchanged and power halved then the intensity should also be halved . From this I get E' = E/2 ...
  25. J

    Electric field varying with distance

    [Moderator note: moved from general physics, no template.] This is a solved example given in the book . Could someone help me understand how amplitude of electric field has an inverse relationship with distance ? Only the very basics of EM waves are covered in the book so I would appreciate...
  26. sergiokapone

    Electric field lines of a sphere in a uniform electric field

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  27. B

    Resistance of a semicircular conductor with a rectangular cross section

    Homework Statement There is a conductor with the square-shaped area. the Radii are r1 , r2 with width b and resistivity ## \rho_R##. Find the resistance R between A and B 2. Homework Equations ##I = \iint_A\vec J \cdot d \vec A## ## \vec J = \kappa \vec E ## ## \vec E = \rho \vec J## ## V =...
  28. BryanDorais

    What is the polarization of the following wave?

    What is the polarization of the following wave? E = (x 20∠0 + y 20∠90°)e-j3z, where x and y are unit vectors I haven't been able to make an attempt because i have no idea how to start and none of the equations i got in class seem to apply. I know that polarization refers to the direction that...
  29. M

    Electric field of two conducting concentric spheres

    Homework Statement Two conducting hollow spheres are are placed concentrically, the inner sphere have a radius ra = 5 cm and the outer sphere have a radius rb = 15 cm. The charge on the inner sphere is qa = 4 · 10−7 C and qb = −4 · 10−7 on the outer sphere. (a) Use Gauss’s law to find the...
  30. Tom MS

    Why Does Diatomic Hydrogen Form Despite Zero Net Electric Field?

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  31. T

    Electric Field between two flat metal plates

    Homework Statement Two large, flat metal plates are held parallel to each other and separated by a distance d.· They are connected together at their edge by a metal strip. A thirt plastic sheet carrying a surface charge \sigma per unit area is placed between the plates at a distance 1/3*d from...
  32. T

    Find the x component of the Electric Field

    Homework Statement Find the general formula for the x component of the electric field if the charge density p varies only with x throughout all space. Homework EquationsThe Attempt at a Solution I started using the poisson equation \bigtriangledown \bullet \bar{E} = \frac{p}{\varepsilon_{0}}...
  33. R

    Particle motion + electric field when voltage varies

    Homework Statement Two parallel plates located at a distance "L" from each other they maintain a potential difference "V" because of a battery (as shown in the picture). Through a small hole, made in bottom plate, electrons get into system (with mass "m" and charge "-e"), with velocity "v" and...
  34. F

    Electric field of a current carrying conductor along its sur

    Homework Statement I am trying to figur out whether there is or isn t an Electric Field along the surface of a cylindrical current carrying wire With radius r and length L, current I and resistance R. I was trying to see if someone already asked this and i found one discussion, however where a...
  35. Fibonacci Vonacci

    Magnetic Field of an AA Battery 'Immersed' in a Conductor

    If an AA battery were placed in some kind of ideal conducting 'ether': 1) Would current flow, and if so, what would the flow of electrons look like? 2) How would the magnetic field look? (I imagine that if there was an electric current flowing, that the magnetic field would look a little like...
  36. E

    Why is the electric field in an ideal wire zero?

    I’ve looked at the answers given to the previous times this question has been asked, but I still don’t seem to understand how this holds in the case of a closed circuit. Here’s an explanation given before: “Think of the wire as a horizontal cylinder. If you apply an electric field pointing to...
  37. Fraser MacDonald

    What is the electrostatic force field?

    I have just covered the electricity unit in my advanced higher physics course, and have happily accepted that a force is created between charged particles. I understand that coulombs law can be used to calculate this force, but here is my question. What actually is this force between the charged...
  38. G

    What about the electric field in a circuit with resistors?

    Hi. I am having some trouble understanding what is the voltage drop in a system with resistors in series. If there is a difference of electric potential between two points in space, since electric potential is electric potential energy per charge, there is a difference in the electric...
  39. Mary1995

    Equilibrium Stability: Finding Charge Stability

    Homework Statement The equation x^2+3x-0.45=0 has two solutions x1=0.14 and x2=-3.14, these are supposed to be the locations at which the electric charge is in equilibrium with two other charges, should I use the first derivative to see at which location the charge will be stable? Homework...
  40. R

    Ratio of electric field to applied magnetic field

    Homework Statement A metal rod of mass M and length L is pivoted about a hinge at point O as shown in Figure P32.80 (I have attached this to this post) The axis of rotation passes through O into the page. Find the ratio of the maximum electric field inside the rod to the applied magnetic field...
  41. G

    Electric field due to semi-circular wire at a distance

    Homework Statement A semi-circular wire containing a total charge Q which is uniformly distribute over the wire in the x-y plane. the semi-circle has a radius a and the origin is the center of the circle. Now I want to calculate the electric field at a point located on at distance h on the...
  42. G

    Electric field in a capacitor with a dielectric

    Homework Statement A parallel plate capacitor has 2 square plates of side l, separated by a distance d (l is a lot bigger than d). Between the plates, there is a linear and non-homogeneous dielectric with constant $$\epsilon_R=1+ay$$ with $$a$$a positive constant. Calculate the electric field...
  43. K

    Electric Field and Kinematic Equations for Acceleration and Time Calculations

    Homework Statement Homework Equations F=qe, a= qe/ma, x= vit + 1/2t^2 The Attempt at a Solution (a) i used the formula a= qe/ma to calculate the acceleration and then substituted in this kinematic equation x= vit + 1/2t^2 then i solved for t taking the initial velocity as zero. (b) i used...
  44. rocdoc

    About the first-order electric field correlation function.

    For a fixed point in space, the first-order electric field correlation function may be given as (Possibly incorrectly, see my "second" post to this thread)! $$\langle\vec E^*(t)\vec E(t+\tau)\rangle = {\frac {1} {T}} \int_T\vec E^*(t)\vec E(t+\tau)dt~~~~~(1)$$ Where T is a very large time and *...
  45. K

    Electric field model using a cylindrical capacitor

    Homework Statement In a lab experiment we measured the potential at different points within a cylindrical capacitor electric field modeling plate thing (apparently that's the best I could do to translate that into English). The positive electrode was connected in the middle and the negative...
  46. S

    Small oscillations and a time dependent electric field

    Homework Statement [/B] Here's the problem from the homework. I've called the initial positions in order as 0, l, and 2l. Homework Equations The most important equation here would have to be |V - w2*M| = 0, where V is the matrix detailing the potential of the system and M as the "masses" of...
  47. P

    The electric field in an expanding, statically-charged tube

    Imagine that I have a straight, statically-charged, cylinder-shaped tube with arbitrary (ideally infinite) extent. The charge is distributed evenly over the tube such that the field inside the tube is zero. For convenience, let's line up the tube centered along the x-axis such that the...
  48. E

    How to find electric field given points of electric potentia

    I have what at first seems like a very simple problem, yet I have no clue how to solve it. There is 1 point defined to have 0V, and another point has exactly 1V. Assume there is nothing else in the universe. https://i.imgur.com/iv9oL5j.png How do I find the electric potential and field at any...
  49. P

    Induced Electric Field In Circuit With Varying Resistance

    Homework Statement This is irodov's problem #310 in electrodynamics A long solenoid of cross-sectional radius a has a thin insulated wire ring tightly put on its winding; one half of the ring has the resistance ## \beta ## times that of the other half. The magnetic induction produced by the...
  50. maxelcat

    Field between two parallel postive plate different voltages

    Homework Statement This was a one mark question on an AS paper. [/B]Homework Equations [/B]The Attempt at a Solution Mark scheme says straight lines, equally spaced lines pointing down and starting/ending on the plates. (which I totally get if one plate was 0V or negative) However, if you...
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