What is Electric field: Definition and 1000 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. D

    A (nonconservative) electric field is induced in any region in which...

    TL;DR Summary: A (nonconservative electric field is induced in any region in which) A. there is a changing magnetic flux B. there is a changing magnetic field C. the inductive time constant is large D. the electrical resistance is small E. there is electrical current there can be more than one...
  2. Idontknowhatimdoing

    Electric Field Inside Cylindrical Capacitor

    we know that flux is equal to the area integral of electric field dotted with dA and we can set this equal to charge enclosed divided by epsilon naught. Thus, in this case, the integral simplifies to E * A = (q_enclosed)/(ε_naught) when we choose a cylindrical gaussian surface with radius of r...
  3. notgoodatphysics

    Electric field of a cylinder given the electric field of a ring

  4. F

    Magnitude of the Line Charge Density of a Power Line

    Okay so I am a little confused as to where I made a mistake. I couldn't figure out how to program Latex into this website but I attached a file with the work I did and an explanation of my thought process along the way.
  5. J

    Struggling With Part C of Electric Field Calculation

    I've figured out parts A and B but I'm struggling with Part C. I used the equation V = kQ1/r1 + kQ2/r2 where Q1 = -4.4e-12C ; k = 8.98755e9 r1 = 0.026 m Q2 = 27.4e-12 and r2 = .051-.026 My answer (8.329 V) is wrong but I have no idea why. Please help if you can.
  6. V

    Why is electric field at the center of a charged disk not zero?

    The electric field strength at the center of a uniformly charged disk should be zero according to symmetry of concentric rings about the center, where each ring is contributing to the electric field at the center of the disk. For a thin ring of uniform charge distribution the formula is ##E =...
  7. Pushoam

    Electric field at a point close to the centre of a conducting plate

    Since the electric field due to a conducting plate is twice the electric field due to a plastic plate having same charge density, the electric field at the point P will be twice in case of conducting plate and hence it is 20 volt per metre. Is that correct?
  8. B

    A Energy levels shifts in a time-varying electric field

    Hello! I have 2 levels of the same parity with energies ##E_1 < E_2##, and another level of opposite parity a distance ##E## from the ##E_2##. I also have that ##E_2 - E_1 << E##. I have a laser on resonance (I am trying to scan along the resonance and find it) with the transition from ##E_2##...
  9. N

    Proving SHM for charged spring mass system in electric field

    For part (f) Solution is I don't understand why the bit highlighted in yellow is true. Would anybody be kind enough to help.
  10. C

    Electric field at surface of lead-208 nucleus

    For this problem, The solution is, However why is ## r = (208)^{1/3}(1.20 \times 10^{-15} m)## Many thanks!
  11. C

    Integrating electric field of rod

    For this problem, However, I am trying to solve this problem using an alternative method compared with the solutions. My method is: ##\vec E = k_e \int \frac {dq} {r^2} \, dx ## ##\hat r## ##\vec E = k_e \int \frac {\lambda} {x^2 + d^2} \, dx## ## \hat r## If I let ## \hat r = \frac {-x\hat i...
  12. M

    I Electric field in a rotating frame

    Hello! I have a radially pointing electric field i.e. at a given radius, R, the electric field has the same magnitude and points radially around that circle of radius R. I have a particle moving around that circle of radius R, with uniform velocity (ignore for now how it gets to move like that)...
  13. C

    Electric field due to n charges

    For this problem, The solution is, However, should they be a vertical component of the electric field for the expression circled in red? I do understand that assuming that when the nth charge is added it is placed equal distant for the other charges so that a component of the electric field...
  14. C

    Electric field due to two charges

    The problem and solution is, However, I would like to know why it cannot be solved like this: Thanks for any help!
  15. C

    A How to define ##\nabla \cdot D ## at the interface between dielectrics

    It is believed that Maxwell equations (together with other relations depending on the materials) are sufficient to account for any electromagnetic macroscopic effect. The problem is that, for a Maxwell equation to hold, it must at least be defined. Consider for example the case of two...
  16. noowutah

    Find the electric field of a long line charge at a radial distance

    TL;DR Summary: Find the electric field of a long line charge at a radial distance where the potential is 24V higher than at a radial distance r_1=3m where E=4V/m. Answer: 29.5V/m. Never mind: I retract this question. The integral apparently is supposed to diverge! I apologize for not reading...
  17. C

    Symmetry behind charged spring-mass system in Electric field

    For this problem, If we assume that x = 0 is where the spring connects to the wall, then the rest position of the mass-spring-electric field position is x = EQ/k and the max position is x = 2EQ/k. Is there a reason for the symmetry between the rest position and max position? (The symmetry...
  18. C

    No Limits of Integration for Electric Field Integral?

    For this problem, The solution is, However, why have they not included limits of integration? I think this is because all the small charge elements dq across the ring add up to Q. However, how would you solve this problem with limits of integration? Many thanks!
  19. C

    Finding Area of Ring Segment to Find Electric Field of Disk

    Hi! For this problem, Why is the area of each ring segment dA equal to (2π)(r)(dr)? However, according to google the area of a ring segment (Annulus) is, Many thanks!
  20. C

    Electric Field of a Uniform Ring of Charge

    Hi! For this problem, The solution is, However, why did they not include constants of integration in their working shown in red? Many thanks!
  21. livio

    Estimates of voltage drop with distance in weak electric field

    If I resolve the equation in 0, imposing a voltage value of 5 mV, it gives a non real solution, therefore I cannot resolve it for R=1 because I do not know which voltage value to impose. I am sure this is simpler than I am putting it :) thanks for any advice!
  22. C

    Why Does Positive Charge Exert Elec. Field Beyond Neg. Charge?

    I wonder how it is possible that a positive charge can exert el. field beyond negative charge? Shouldn't they "connect" and therefore positive charge should stop to have el. field beyond neg. charge? I mean, I am obviously wrong about that, but can someone please explain why/how el. field from...
  23. cwill53

    Average Electric Field over a Spherical Surface

    The picture above shows the integral that needs to be evaluated, and the associated picture ## \cos\alpha ## can be obtained via the law of cosines. I'm simply confused as to where the ##\cos\alpha ## comes from in the first place. I just don't see why ##\cos\alpha ## is necessary in this...
  24. N

    Find the Electric field at point p

    Since q3=q4 and they are opposite to each others they cancel out But as soon as I try to find the electric field of one of the charges, I need the radius which is not given. By isolating the electric field for radius E=(kq)/r^2 I now have two unknowns
  25. Povel

    A Exploring the Electric Field of a Moving Charged Spherical Shell

    The electric field inside a charged spherical shell moving inertially is, per Gauss's law, zero. If the spherical shell is accelerated, the field inside is not zero anymore, but it gains a non-null component along the direction of the acceleration, as mentioned, for example, in this paper. The...
  26. Y

    Electric field of charged rod

    hello i would like to understand to something. here is the drew now for my question: i was able to find Ey and here is my correct answer: when i try to find Ex i didnt understand something, i found the correct answer but i need to put minus before and i want to know why? here is my solution...
  27. H

    I Why is the electric field in y direction in a TE guided wave?

    Hi, I have a fairly simple question, but the answer is probably not as simple. I'm not sure to understand why in a guided wave (TE), the electric field is in the y direction. I know ##E_z = 0##, but why ##E_x = 0, B_y = 0##?
  28. N

    I Questions about a Conductor in an Electric Field

    Dear PF, I have a question regarding a conductor in electric filed. I have formulated my question in attached PDF file ... would please be so kind and advise me please... Thanks you in advance ...
  29. S

    I Brownian motion of charged particles?

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  30. P

    Engineering Electric field in spherical shell - trying to understand the location

    Nevermind.
  31. H

    Why Does the Electric Field Sum Instead of Cancel with Opposite Charges?

    If there are two charges positive and negative and their electric field point in the same direction then the total electric field would be their sum of magnitudes. Why don't we consider the sign of the charges? For example, a parallel plate capacitor is inside the region where both the positive...
  32. ermia

    Electric field needed to tear a conducting sphere

    ..
  33. josephsanders

    I Tangential electric force at a surface

    Suppose you have an infinite plane of charge. If the surface charge density is uniform, would the tangential electric force always be zero, even if it is not a conductor nor static? My thought process for this is that if you look at each point charge and draw the electric field lines, then at...
  34. ermia

    Electric field of a part of a hemisphere

    I tried gauss law. And the fact that if alpha is less than pi/2 we can say that we have two parts with angle alpha and one other part which has a normal field at the center. But non of them helped me answer. The problem's solution says that we can use the fact that our section has longitudinal...
  35. Ahmed1029

    I How do I find the Direction of an induced electric field?

    Faraday's law tell's you about the line intergal of the electric field, but you have to know the direction of the induced electric field first in order to properly apply it. How can I find its direction? Is it in the same direction as the induced current?
  36. warhammer

    B Direction of Electric Field & Field Due to a Dipole

    Hi all. I am stuck with a seemingly silly doubt all of a sudden. The direction of Electric Field is taken from Positive to Negative (because Field Lines originate from a Positive Charge and terminate at Negative Charge). We know that direction of Dipole Moment is from Negative Charge to a...
  37. P

    Calculating eletric potential using line integral of electric field

    So, I am able to calculate the electric potential in another way but I know that this way is supposed to work as well, but I don't get the correct result. I calculated the electric field at P in the previous exercise and its absolute value is $$ E = \frac {k Q} {D^2-0.25*l^2} $$ This is...
  38. warhammer

    I Electric Field & Interplay between Coordinate Systems | DJ Griffiths

    Hi. I believe I have what may be both a silly and or a weird query. In many Griffiths Problems based on Electric Field I have seen that a coordinate system other than Cartesian is being used; then using Cartesian the symmetry of the problem is worked out to deduce that the field is in (say) z...
  39. V

    I Electric field of a moving charge that's abruptly stopped

    Hello everyone, This is in reference to fig 5.19 (screen shot attached - please read the paragraph which says "Figure 5.19 shows the..."). I don't get why the field outside of the sphere of radius ct acts as though the particle would have continued its motion. Author's words : "The field...
  40. Tesla In Person

    Electric field strength at a point due to 3 charges

    I got E. 13q as the answer. That is what i did: The electric field due to +q at origin 0 should equal the electric fields of charges -3q and the new charge placed at 2x. So applying the equation above like this; k*(q) / (2^2) = -3q*k + (k*C)/ 4 solving for C the new charge added, gives 13q. I...
  41. Tesla In Person

    Flux of Electric field through sphere

    My attempt: We have 3 charges inside 2 +ve and 1 -ve so i just added them up. 4 + 5 +(-7) = 2q Then there is a -5q charge outside the sphere. I did 2q + (-5q)= -3q . The electric field flux formula is Flux= q/ E0 . So i got -3q/E0 which is obviously wrong : ) . After quick googling , I...
  42. Tesla In Person

    Electric Field Inside a Conducting Sphere: Is it Always Zero?

    Is the electric field inside a sphere always 0? Even if we have charges on the surface?
  43. HelloCthulhu

    How does an electric field create velocity in a water bridge?

    I've been researching water bridges and electrowetting to learn the effects of electric fields on water molecules but something continues to confuse me: if polar molecules can only rotate in an electric field, how is the water moving? Anyone familiar with this phenomenon? Any help is greatly...
  44. A

    Understanding Torque in a Magnetic Field with Loop

    I am confused about this, do the black arrows represent the direction of magnetic force? The torque ##\tau = -IABsin\theta##, where I = current A is area of loop and B is magnetic field strength and I am a little confused how ##\theta## here is 45 degrees when the angle between the normal for...
  45. link223

    Calculating the Electric field for a ring

    What i don't understand is why we are able to replace the ring with 'two oppositely charged superposed disks'? Just trying to understand.. So we have a uniform charge which means that this'll just be a simplification of the problem than, correct? Thanks in advance.
  46. A

    Voltage Drop in Parallel Receptacle Wiring

    I know how to solve the question but I am a bit confused about why there is a current of 3 A and a voltage of 110 V requirement for the refrigerator but the power plant only supplies 110 V. How can there be a voltage drop on the refrigerator load of 110 V, when there is also a voltage drop on...
  47. A

    Gaussian cylinder enclosing cylinder of charge

    I am confused why we don't take into account the lids of the cylinder since the Gaussian cylinder is of finite height L as shown in the image
  48. BnayaMeir

    Surface Current and Electric Field

    Hi everyone! I'm pretty new in this forum, I found the topics here very relevant to my physics course. And here is my question: Given the following drawing, two infinite sheets (in y and z axis) of ideal conductive material. their thickness is infinitesimal (dx->0). The electric field is...
  49. A

    Understanding Electric Field of Positive & Negative Plates

    I am confused with the solution. It says ##\vec E = \frac{\sigma}{\epsilon_0}##. Shouldn't E = ##2*\vec E = 2*\frac{\sigma}{\epsilon_0}##? Electric field of the positive plate and electric field of the negative plate.
  50. A

    I Electric field is zero in the center of a spherical conductor

    Electric field is 0 in the center of a spherical conductor. At a point P (black dot), I do not understand how the electric field cancels and becomes 0. Electric field is in blue.
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