Electrostatics Definition and 684 Threads

Electrostatics is a branch of physics that studies electric charges at rest.
Since classical physics, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber, ήλεκτρον, or electron, was thus the source of the word 'electricity'. Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described by Coulomb's law.
Even though electrostatically induced forces seem to be rather weak, some electrostatic forces such as the one between an electron and a proton, that together make up a hydrogen atom, is about 36 orders of magnitude stronger than the gravitational force acting between them.
There are many examples of electrostatic phenomena, from those as simple as the attraction of the plastic wrap to one's hand after it is removed from a package to the apparently spontaneous explosion of grain silos, the damage of electronic components during manufacturing, and photocopier & laser printer operation. Electrostatics involves the buildup of charge on the surface of objects due to contact with other surfaces. Although charge exchange happens whenever any two surfaces contact and separate, the effects of charge exchange are usually only noticed when at least one of the surfaces has a high resistance to electrical flow. This is because the charges that transfer are trapped there for a time long enough for their effects to be observed. These charges then remain on the object until they either bleed off to ground or are quickly neutralized by a discharge: e.g., the familiar phenomenon of a static "shock" is caused by the neutralization of charge built up in the body from contact with insulated surfaces.

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  1. M

    System of non-linear partial differential eqs from electrostatics

    I have an electrostatics problem (shown here: https://www.physicsforums.com/showthread.php?t=654877) which leads to the following system of differential equations: \frac{\partial E_z}{\partial z}=\frac{\rho}{\epsilon_0} (1) Z_i E_r \frac{\partial \rho}{\partial r}+(u_g+ Z_i E_z)...
  2. J

    Electrostatics: Surface charge density-numerical solution

    Hi, I'm very new here, 10min old, but the problem with my knowledge, or better, lack there of, at this time is very hard, so I need help. I am trying to numerically calculate a certain electrostatic problem (attached an image "prob.jpg" to clarify). I have a disk at potential V0, and with this...
  3. I

    Several questions on an experiment on electrostatics

    Move a can without touching it 1. Place an empty aluminium can on a table so that it can roll freely. 2. Rub an inflated rubber balloon on your hair. 3. Hold the rubbed balloon several centimetres away from the can and move it away from the can slowly. 4. Put the balloon on the opposite side and...
  4. S

    How is the rubber comb and wool example a demonstration of electrostatics?

    i have read an example on electrostatics that if anyone rub a rubber comb and wool , the rubber comb acquires the ability to attract small pieces of paper . this is due to the comb becomes negetively charged and wool becomes positively charged . now the book tells that some electrons of the...
  5. R

    Electrostatics (Gauss’s law for sphere)

    Homework Statement I have some difficulty understanding a part of the following solved problem: Use Gauss's law to find the electric field inside a uniformly charged sphere (charge density ##\rho##). Answer: ##\oint E.da = E.4 \pi r^2 = \frac{1}{\epsilon_0} Q_{enc} = \frac{1}{\epsilon_0}...
  6. X

    What principles does a photostat machine use to operate?

    What is the Application of xerography ? I mean on what principals does the photostat machine works...
  7. P

    Electrostatics question. just need a bit direction.

    I was trying to solve this one, but couldn't come up with any way to start. In 1959 Lyttleton and Bondi suggested that the expansion of the Universe could be explained if matter carried a net charge. Suppose that the Universe is made up of hydrogen atoms with a number density N, which is...
  8. S

    Electrostatics questions, parallel plates, force, field

    Homework Statement 1. A 2*10^-6C charged object is .40m left of an another 2*10^-6C charged object, with a 3*10^-6C charged object .40m to the right of the centre object, creating three charged objects in a line. Calculate the magnitude of the net electric force on the centre charge due to...
  9. F

    Electrostatics balancing gravitational, coulomb forces and tension

    Homework Statement Hi, I'm on the first part of this question and I've got to the end but I have an extra factor of two which I can't seem to explain! Any insight would be much appreciated, thank you! Homework Equations The Attempt at a Solution I resolved the forces around one ball and came...
  10. D

    Electrostatics: Using a conducting string suspension.

    Homework Statement This is a lab question. Basically what the lab entails is we have two spheres. One is suspended from a string and another is attached to a non-conducting rod. We inductively charge the sphere attached to the rod. Then we bring it close to the other sphere that is being...
  11. B

    Electrostatics: force calculation

    Homework Statement Is there a way to nicely compute the force between two configurations of point charges ? Here is an example. Two "squares" of charges (each separated by a rigid insulator of length a) are separated by a distance d, measured with respect to their centers. Instead of taking a...
  12. H

    Calculating Work and Energy in Electrostatic Systems

    Homework Statement I decide to use electric charges to move a 1000 kg box up a 30 degree frictionless ramp. I decide to put equal and opposite charges on the box and at the top of the 5.9 meter ramp. Basically there is a right triangle with a box at the bottom with +q written next to it. The...
  13. J

    Cambridge Physics Problems: Electrostatics

    Before I go about trying to futilly solve the question, is this thing beyond a CIE A-Lv physics student's reach or not? Any comments on the difficulty of the question, and perhaps the reading material which you would recommend before I attempt the question? Thank you.
  14. L

    How Many Electrons are Needed to Create a Force of 10^-19 N Between Two Spheres?

    1. Homework Statement : the excess(equal in number) of electrons that must be placed on each of two small spheres spaced 3 cm apart, with force of repulsion between the spheres to be 10^-19N, is...? 3. The Attempt at a Solution : since, f=kq^2/r^2. ive calculated q from here which is...
  15. Saitama

    Electrostatics and velocity question

    Homework Statement Electric field given by the vector \vec{E}=x\hat{i}+y\hat{j} is present in xy plane. A small ring carrying charge +Q, which can freely slide on a smooth non conducting rod, is projected along the rod from point (0,L) such that it can reach the other end of the rod. What...
  16. P

    Physics electrostatics question

    i just can't seem to figure out what is the effect of temprature on dielectric constant of a medium. since, K=ε/ε0, therefore according to me there is no effect of temperature as temperature is not in the formula. Please help.
  17. N

    Help with electrostatics : Charging and reconnecting a capacitor .

    Homework Statement So I came by this question yesterday which was in Solved examples part of my Textbook . I looked at the Solution and was not able to figure out how ? The Question says . A 5uF capacitor is first charged by applying a Potential Difference of 24 V . a different...
  18. M

    Work and Energy Loss; Electrostatics

    Griffith's Problem 2.40 (a) and (b) Suppose the plates of a parallel-plate capacitor move closer together by an infinitesimal distance ε, as a result of their mutual attraction. a) Use P= \frac{\epsilon_0}{2}E^2 to express the amount of work done by the electrostatic forces, in terms of...
  19. D

    Role of mass in this problem on electrostatics

    Homework Statement Positive charge Q is distributed uniformly over a circular ring of radius R.A particle with mass 'm' and a negative charge 'q' is placed on the axis at a distance 'x' from the centre.Find the force on the particle.Assuming x<<R, find the time period of oscillation of the...
  20. fluidistic

    Electrostatics, force applied on a charge

    Homework Statement First of all, in order to avoid any confusion, let me precise that I use Gaussian units. I.e. k=1 rather than \frac{1}{4\pi \varepsilon _0}. An infinite conductor plane is kept at a potential worth 0. A point-like charge can be found at a distance d from the plane. Using the...
  21. T

    Proof of symmetries in electrostatics

    I need a mathematical proof that should indicate the following: The direction of the electric field must be radial, for a spherical charge distribution to remain invariant after applying a rotation matrix to its field. Analogously how can we prove that the electric field of a infinite...
  22. D

    Calculating Repulsive Force between Two Charges at Different Distances

    Homework Statement two equal charges repel one another with a f = 4.0x 10^-4N when they are 10cm apart. If they are moved until the separation is 5.0 cm, the repulsive force is... Homework Equations f= kq1q2/r^2 The Attempt at a Solution I already calculated and I just would like someone...
  23. fluidistic

    Electrostatics, conductor infinite sheets

    Homework Statement Two infinite plane lattices (conductor) of uniform thickness t1 and t2 respectively, are placed parallely to each other with their adjacent faces separated by a distance L. The first lattice has a total charge by unit of area (the sum of surface densities of each sides of...
  24. H

    Electrostatics - point charges and work

    Electrostatics -- point charges and work Homework Statement A 3.0 μC point charge and a 9.0 μC point charge are initially infinitely far apart. How much work does it take to bring the 3.0 μC point charge to x = 3.0 mm, y = 0.0 mm and the 9.0 μC point charge to x = -3.0 mm, y = 0.0 mm? (The...
  25. jinksys

    Electrostatics - Coulomb's Law

    I'm doing example 2.1 in Griffith's Electrodynamics book. Can someone explain where the cos(theta) comes from in the formula for dE? The formula is on the first image: Here.
  26. S

    Electrostatics: Creating Charged Objects

    An iron arrowhead has an initial charge of 2.100e-6 C. How many electrons are required to give it a charge of −2.82 μC? I know that e (the elementary charge) = +/- 1.602E-19 C And N is the number (or excess charge) I tried solving this problem 2 ways. The first way: (2.100E-6 -...
  27. A

    Electrostatics -Electric Field and Potential

    Homework Statement A 30 cm diameter metal sphere hangs from a thread in the middle of a very large room. So its surroundings are essentially at infinity. If the electric field at tis surface is equal to the break down strength of air 3MV/m, what is the absolute potential at the center of the...
  28. D

    Electrostatics and Coulomb's law

    Homework Statement +2μC -2μC 0------------0 | | | | | | 0------------0 +2μC -2μC This is a square Each side in .2 (no units) Find the magnitude and direction of the electric field at the center of the square...
  29. U

    Magnetism seems absolute despite being relativistic effect of electrostatics

    I know that magnetic force due to a current carrying wire on a test charge moving w.r.t the wire(along the wire), can be interpreted as the electrostatic force if we use the first order relativistic corrections for Time Dilation or Length contraction of the charges of the wire, in the frame of...
  30. S

    Is the Electric Field Inside a Nonconducting Charged Hollow Sphere Zero?

    What is the electrical field inside a nonconducting charged hollow sphere? My Explanation: In both cases, conducting and nonconducting hollow sphere, the flux inside is zero because there is no charge inside However in conducting sphere electrical field is zero anywhere inside due to...
  31. G

    Electrostatics problem: solve for where E=0 given a configuration of charges

    Hey everyone, thanks for taking a look at this. I was hoping you could look over this to make sure I solved this correctly. Thanks for you time. Homework Statement ---- "+" ---- "+" ---- "-" ---- Given this configuration of charges where the plus and minus indicate the magnitude of...
  32. F

    Electrostatics - Electron passing through charged plates

    Homework Statement http://img716.imageshack.us/img716/7692/picture8sj.png Homework Equations ΔEp=QV Ek=0.5mv2The Attempt at a Solution I'm making sure I understand what's going on here. Please bare with me. ΔEp = Ek .5mv2 = Q(1200+V) Solving for V, I get -642V. In a nutshell, is this what...
  33. V

    Understanding Green functions in electrostatics

    Hey guys! So I'm reading Jackson's Classical Electrodynamics, and I'm trying to get a sense of what Green Functions really are. The book says that "the potential due to a unit source and its image(s), chosen to satisfy homogeneous boundary conditions, is just the Green function appropriate for...
  34. U

    A two conducting balls electrostatics problem

    Suppose there are two conducting balls of the same radius and the balls are separated by some distance. If both balls are at the same nonzero potential and the potential at infinity is zero, does a closed form formula for the potential exist? Since I can't find the problem solved anywhere I...
  35. F

    Electrostatics [Electric Field]

    Homework Statement (Please see attachment) Point P is 5.00 cm from the origin and each charge is 20.0 cm from the origin. Q1= -50.0 nC (20.0 cm from the origin on the -x axis) Q2= +30.0 nC (20.0 cm from the origin on the +x axis) Point P is 5.00 cm from the origin (in the +x axis)...
  36. Telemachus

    Electrostatics, potential between and outside concentric spheres

    Hi there. I have this problem which I was trying to solve, but I couldn't fit the boundary conditions. The exercise says: Two conducting spherical shells with radii a and b are concentrically disposed and charged at potentials φa and φb respectively. If rb>ra, find the potential between the...
  37. V

    Electrostatics, sphere question.

    Homework Statement A spherical conductor A contains two spherical cavities. The total charge on the is itself zero. However, there is a point charge qb at the center of one cavity and qc at the center of other cavity. A considerable distance r away from the center of the spherical conductor...
  38. Telemachus

    Electrostatics, infinite concentric cylindric conductors

    Hi. I have this problem, and when I tried to solve it, some doubts and questions emerged, I need some help with this. The problem says: The figure shows two concentric cylindrical conductors with infinite length. We'll suppose that between them there's a known potential difference. a. Find an...
  39. A

    Electrostatics problem about part of a hollow sphere

    Homework Statement A hollow sphere of radius R, centre at the origin, is cut into eight equal parts by 3 mutually perpendicular planes through the origin. Only one part is retained (the other 7 are removed) and given a charge q uniformly distributed on its surface. find magnitude of...
  40. G

    Basic electrostatics (geometry help)

    Here's the problem: http://i.imgur.com/dS7ZH.jpg I don't understand why the cosine has to be there. My geometry is a bit rusty, but wouldn't it be enough without the cosine part?
  41. Telemachus

    Electrostatics, infinite charged hollowed cylinder

    Hi. I want to know if I did this on the right way. The exercise says: An infinite hollowed cylinder, with the cavity being another concentric cylinder has a uniform charge density. Find the electric field and the potential over all space. And this is how I proceeded. I've called the inner...
  42. M

    Creative ideas for electrostatics demos/labs

    I am trying to put together some demonstrations for E&M class related to the topic of conductors in electric field, particulary that the field inside is zero (something like Faraday cage) and that the field gets stronger with curvature. I have seen videos of the courses with some great...
  43. C

    General questions about conductors in electrostatics

    These are just some general questions I have about what I'm reading in my physics book. I'm really having trouble visualizing what happens to electrons in conductors (this is all for electrostatics btw). Three scenarios: (1) A solid conductor Why is the charge only on the surface of the...
  44. V

    Why Is the Calculated Charge Enclosed Within the Cube Incorrect?

    The displacement vector in a cube is defined by the relation D =(4x*xy + z)i+(4xy)j-(z)k c/m2 . Then charge enclosed within the cube of side 1m is ………….. I know that the displacement vector holds the relation ∇ . D = ρ Where ρ is the charge density. I found ∇ . D and...
  45. C

    How to prove an electrostatics concept mathematically

    "The third point charge should be placed at a location at which the forces on the third charge due to each of the other two point charges cancel. There can be no such place except on the line between the two point charges." i need to be able to prove a similar statement mathematically...
  46. I

    Electrostatics - Finding potential V(r,z) given hyperbolic boundry conditions.

    Homework Statement I'm trying to derive Equation (1) from the paper: http://idv.sinica.edu.tw/jwang/EP101/Paul-Trap/Winter%2091%20ajp%20demo%20trapping%20dust.pdf We are working with a cylindrically symmetric geometry along the z-axis. r^2 = x^2 + y^2 We have electrodes described by...
  47. T

    Electrostatics - Conducting torus and a point charge

    Homework Statement We have a metal conducting torus and a point charge that is located on the torus' axis (location on the axis is arbitrary). Calculate the (influenced) charge distribution on the torus and the electrostatic force on the point charge. Homework Equations Equation for...
  48. L

    Electrostatics problem (electron's motion in cathode ray tube)

    Homework Statement Homework Equations Fq=E*q kinematics equations... The Attempt at a Solution The problem is that in the end I get a value ABOVE the mid-axis instead of below. I don't know what I'm doing wrong. Please check my reasoning. Stage 1: While it's in between the plates where...
  49. L

    What is divergence theorem in electrostatics?

  50. F

    Electrostatics: can a positive charge induce negative potential?

    Can a charge, brought into a chargeless world filled with some geometry of conductors and dielectrics, induce a negative potential anywhere in that world? I feel the answer is no. But I cannot think of a good way to prove it, or even attack the problem. More explicitly, imagine a world...
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