What is Electrostatics: Definition and 675 Discussions

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. T

    Method of Images in Electrostatics

    Homework Statement A point charge q is held a distance d > a below the centre of a large spherical conductor of radius a. Show that, if the spherical conductor is earthed, the potential outside the sphere may be found by placing an image charge at a distance c=a2/d from the centre of the...
  2. S

    Triangle Electrostatics Problem

    Homework Statement Three positive particles of charges +7.0 uC are located at the corners of an equilateral triangle of side 20 cm. Calculate the magnitude and direction of the net force on each particle. Answer: 19.0 N [AWAY FROM THE CENTRE] Homework Equations F = (kQ1Q2)/(r^2)...
  3. C

    Electrostatics Problems (all with worked out answers but wrong)

    Homework Statement 1. A thin rod bent in the shape of a semicircle of radius 20 cm is uniformly charged along its length with a total charge of 8.0 microC. What is the electric field at the center of the semicircle? a. 7.3 x 10^4 N/C b. 8.4 x 10^4 c. 5.7 x 10^4 d. 3.9 x 10^4 e. None...
  4. S

    Numericals On Electrostatics (including Coloumbs Law)

    1. In hydrogen atom the distance between electron(e=1.6*10^-19 C)(Mass of electron=9.1*10^-31 kg) & proton(Mass Of proton=1.7*10^23 C) is 5.3*10^-11 m. 2. Calculate the electrical and gravitational forces between 2 particles 3. Can't do the problem... Please help!
  5. U

    Calculating Potential Difference in a Uniform Electric Field

    Homework Statement A force of 4.30\cdot10^{-2} Newtons is needed to move a charge of 56 microCoulombs a distance of 20 cm in the direction of a uniform electric field. What is the potentioal difference that will provide this force Homework Equations Im trying to find one that would work The...
  6. R

    Electrostatics problem (Spherical surface)

    Homework Statement Find the electric field a distance z above the center of a spherical surface of radius R, which carries a uniform charge density "sigma" Treat the case z<R(inside) as well z>R (outside). express your answers in terms of the total charge q on the sphere.[hint:use the law of...
  7. B

    Solving Laplace equations, electrostatics

    Homework Statement a) Consider a conducting sphere of radius R whose surface is maintained at a potential \Phi(R)=\Phi_0cos\theta. Assuming that there are no charges present (inside or outside), what is the potential inside and outside the sphere? b) Consider a cylindrical conducting can of...
  8. T

    Why do the plates attract in Rene's experiment?

    Hi all I'm new to this forum, and this is my first post. I have a question related to a claim by Ralph Rene, and his 'disproof' of Coulomb's law. Rene was a prominent moon hoax believer and called himself the 'Last Sceptic of Science'. Amongst his claims were his reduction of relativity to...
  9. O

    Fourier Transform Applied to Electrostatics

    Homework Statement How would you solve the one-dimensional Poisson's equation: $\nabla ^2 \phi = \frac{\rho}{\epsilon_0}$ Using Fourier Transforms? $\phi (x) = \int ^{+\infty}_{-\infty} G(k) e^{-i k x} dk$ $G(k) = \int^{+\infty}_{-\infty} \phi (x) dx$ I've been trying to understand Fourier...
  10. B

    Electrostatics: work moving point dipole

    Homework Statement Two electrical dipoles with dipole moments \vec{p}_0=p_0\hat{y} and \vec{p}_1=p_1\hat{y} are located in the xy-plane. \vec{p}_0 i located at the origin and \vec{p}_1 is initially in (x,y)=(a,0). What work is required to move \vec{p}_1 (with unhanged directon) to the point...
  11. B

    Electrostatics: spherical shell

    Electrostatics: spherical shell [SOLVED] Homework Statement A point charge Q_1 is located in the centre of a spherical conducting shell with inner radius a and outer radius b. The shell has total charge Q_2. Determine the electrostatic field \vec{E} and the potential \phi everywhere in...
  12. G

    Electrostatics - infinite plates

    Homework Statement Consider two infinite conducting plates of some thickness with charge 2q and -q. The system is in equilibrium, which means there's no charged particles in motion. Find the charge distribution on the surfaces of each plate. (designated as q1 q2 q3 and q4) Homework...
  13. B

    Another electrostatics question.

    There's no problem as such here, just a bit of confusion I'm having regarding finding the electric field. On the following page, second example, is the equation for finding the electric field above a charged disc http://hyperphysics.phy-astr.gsu.edu/Hbase/electric/elelin.html#c2". I understand...
  14. H

    Why Does Expanding a Charged Spherical Shell Require Work?

    Homework Statement A spherical shell of radius R with uniform charge Q is expanded to a radius H.find the work done by electric forces during the shell expansion given answer is 1/(8pi epsilon) *Q^2(1/R-1/H) my attempt work=-change in P E =Q(V1-V2) =1/(4pi epsilon)...
  15. T

    Electrostatics (conduction) and polarization.

    Homework Statement Describe how a metal sphere on an insulating stand is charged if a positively-charged rod were to touch the sphere. (This is a 5 mark problem, so at least 5 major points should be included in the answer. I am not sure whether I have fully answered the problem.) Homework...
  16. J

    Electrostatics: Moving Charge (comprehension problem)

    I already know what the answer to this problem should be, however I do not understand why that is the case. Homework Statement The negative charge (= -1 micro Coulombs) in the figure below goes from y = -5 to y = 5 and is made to follow the dashed line in the vicinity of two equal positive...
  17. T

    Simple Electrostatics Lab: Clarification

    So I have to do a lab, where I rank common household materials based on electronegativity. I am told to acquire two plastic combs and two pieces of string with which to hang them freely off a table. Besides that, I am to acquire common household materials such as rubber, wool, cotton, glass...
  18. R

    How Do You Calculate Charges in Electrostatic Force Problems?

    Homework Statement Two identical conducting spheres, fixed in place, attract each other with an electrostatic force of 0.0898 N when their center-to-center separation is 39.6 cm. The spheres are then connected by a thin conducting wire. When the wire is removed, the spheres repel each other...
  19. R

    Solve Electrostatics MCQ with Explanation

    Friends, Can anyone solve this mcq on electrostatics with proper explanation If a net charge is given to a solid insulating sphere then: a. it must be distributed uniformly in it's volume b. it may be distributed uniformly in it's volume c. must be distributed uniformly...
  20. R

    How do I determine the energy of a charge at infinity?

    Friends, I am not being able to solve the following problem i would be grateful if anyone could help me out. here is the problem: eight equal point charges each of charge q and mass m are placed at eight corners of a cube of side a. if keeping all other charges fixed a...
  21. L

    Solve -3C, 8C, 4C Electrostatics Problem

    Homework Statement three small identical balls have charges -3C,8C and 4C respectively. they are brought in contact and separated. calculate charge on each ball? Homework Equations q=(q1+q2+q3)/3 The Attempt at a Solution what is the need for dividing by 3. why not simply add the...
  22. N

    Principle of Least Action in Electrostatics

    In Feynman's lecture on the principle of least action, he show that you can describe electrostatics by saying that a certain integral is a minimum or maximum. He states the integral, and goes on to show how it can be used to approximate the capacitance of a coaxial line. I've been able to...
  23. D

    Conductor shielding in electrostatics

    Homework Statement Use Gauss' theorem (and the fact that the line integral of the electric field around a closed loop is zero, if necessary) to prove that a closed, hollow conductor shields its interior from fields due to charges outside. (This is 1.1b in Jackson, and it's not really homework...
  24. W

    Volume enclosed by isosurfaces in electrostatics

    Imagine that you have N points scattered in the plane. Each point is charged and contributes to the total potential the same Coulomb potential proportional to 1/r. Now consider some equipotential line of the total electrostatic potential. Is there an analytical expression for the surface...
  25. A

    Electrostatics - parallel plate capacitor

    Two parallel uniform charged circular conducting metal disks contains a charge of +Q and -Q on the inner surfaces, and little amounts of charge +q and -q on the outer surfaces. The detail is shown in the diagram. Each plate has a radius R and thickness t. The separation of the plates is d...
  26. S

    COMSOL electrostatics question

    Hello, I am trying to use the electrostatics module in COMSOL ( I just started a few days ago). The other day, I was able to create a 2D box, apply a charge at one side (via boundary condition), and ground the other sides. I solved, and got a neat output, that I suspect is correct. Then...
  27. T

    Electrostatics: Two charged balls with attraction

    Hi, I have an exam coming up soon. But I thought I would clear my doubts ahead of time. 1. A fixed conducting ball has charge q1= 3X10^-6C. An identical ball with charge q2 is held at a distance x away from q1. The two balls attract each other with a force of 13.5N. The balls are then...
  28. S

    Exploring the Differences in Electrostatics between 3D and 2D Dimensions

    I have asked this question before in another section of the forum but I still don’t have an answer so I thought I would try here. Ok…here goes.. In three dimensions, Poissons equation can be used to model an electrostatic problem in which there is a single point charge at the origin. The...
  29. S

    Physics of Spring with Electrostatics

    Homework Statement Consider a simple 3-body problem in one dimension. One body (the projectile) has mass m. The second body (the target) is made up of two "atoms" each of mass M/2 (total mass = M). Assume an internal spring holds the two atoms together. If the projectile is sent toward the...
  30. K

    What is the Electric Field at the Center of a Square with Four Charges?

    Homework Statement Hello, 4 charges of equal magnitude are placed on the corners of a square of length a. The two charges at the top of the square are negative, while the two charges at the bottom of the square are positive. what is the magnitude of electric field at the centre of the...
  31. P

    A question about electrostatics / Gauss's law

    Homework Statement Suppose a conducting spherical shell carries a charge of 3.00 nC and that a charge of -2 nC is at the center of the sphere. If the distance from the center to the inner shell is 2.00 m, and the distance from the center to the outer shell is 2.40 m, find the electric field...
  32. Saladsamurai

    Simple Electrostatics Problem (Conceptual)

    Part C The answer is zero. But I am not sure what I am missing. I am using a Pentagon to do the analysis (I don't feel like drawing a 13-sided object). It seems like I need to know a little more about the geometry of a Pentagon. How is the center of an odd-number-of-sides polygon...
  33. J

    Van de Graff Generator: Electrostatics, why do objects repel the generator

    Homework Statement a) Why do pie pans fly off the Van de Graff Generator when turned on? b) When foam peanut are placed inside a pie pan with the Generator turned on, what causes the foam peanuts to fly out? c) Why does a person's hair stand up when they touch the generator...
  34. W

    Symmetry and Electrostatics

    Homework Statement Past exam question: Briefly explain the roles of symmetry, uniqueness and superposition in solving electrostatics problems. Homework Equations N/A The Attempt at a Solution I know the definition of these words and could cobble together an answer from that - but...
  35. L

    Very stuck on electrostatics question

    State Gauss' Law A spherical volume carries a uniform charge density \rho_0. A particle of mass m and charge -q is placed inside the sphere at radial distance r. (This additional charge does not distort the field arising from the \rho_0 charge density.) Show that the particle oscillates...
  36. L

    (Electrostatics) Energy of a configuration

    Homework Statement For a given configuration i found the scalar potential \phi(r)-->(as you can see its a function only of r) My question is about calculating the energy of the system. Homework Equations W=-\dfrac{\varepsilon_0}{2}\int |\nabla \phi|^2 d^{3}x =\dfrac{1}{2}\int...
  37. L

    Why doesn't my method for finding electric flux through a cube work?

    A point charge Q is placed at the centre of a cube. What is the electric flux through each face of the cube. ok so the answer is to say that since the cube is a closed surface, Gauss' Law tells us that the total flux through the cube is \frac{Q}{\epsilon_0} and then from symmetry 1/6 of that...
  38. U

    Electrostatics and infinately charged plate question driving me nuts

    Homework Statement An electron is released from rest 2.0 cm from an infinite charged plane. It accelerates toward the plane and collides with a speed of 1.0x10^7m/s. What is the surface charge density of the plane?The answer is 2.52×10−7 C/m^2 ! Homework Equations v=d/t, d=0.5at^2...
  39. T

    An interesting problem in electrostatics.

    There is a cunducting hollow sphere. We know if we charge it all the charges will stay at the outer surface. But if we drill a hole of radius r(say) then what fraction of the charge will remain inside and outside surface I think it is logical to think that less charge will stay in the...
  40. U

    Method of Images (Electrostatics)

    Homework Statement A grounded spherical shell has inner radius of 1m. and outer radius of 2m. Q1=1 Coul. is located at x=0.5m and Q2=-2 Coul. is located at x=4m, respectively. Homework Equations Find the charge system to find the potential outside the shell. Find the charge system to find...
  41. D

    How Does the Electric Field Vary at Point Z in a Dipole Setup?

    given a dipole as in the diagram (http://picasaweb.google.com/devanlevin/DropBox?authkey=Gv1sRgCL_4l4PpvP_YsQE#5311991019489958690 ) with charges of +q and -q placed a distance of "d" from one another. a) what is the electric field at point z, on a line 90 degrees to the middle of the dipole...
  42. D

    Electrostatics, coulomb force between 2 charges

    in a mass of 12g of carbon there are NA= 6.02215x1023 atoms, each atom has 6 electrons, 6 protons and 6 neutrons. each electron has a charge of -1.6x10-19C and each proton has a charge of 1.6x10-19C, each neutron has no charge. if all the electrons were at the north pole and all the protons at...
  43. D

    Electrostatics 1st year engineering

    at each corner of a rhobus , made of rods, each with a length of B, there are electric charges of "Q" and "q" so that each q charge is opposite a q charge and each Q charge opposite a Q charge. what does the ratio of Q/q need to be so that the angle (alpha) is a)90 degrees b)60 degrees c)45...
  44. N

    Electrostatics - Compute the electric charge

    Homework Statement three point charges q1,q2&q3 are place at the vertices of triangle as shown in the diagram charge q1 has been given 4.5 X 10^13 extra electrons, charge q2 given 9.0 X10^13 extra electrons and q3 has had 9.0 X 10^13 electrons taken from it. Calculate the electric charge of...
  45. K

    Electrostatics problem inslator and a conductor problem

    Homework Statement A. Two infinite thin sheets of charge are placed perpendicular to the x axis. The surface charge densities of the two plates are (SC density 1 = 8.5 C/M2) and (SC density 2 = 1.5 C/M2. Placed near plate 2 is a think conducting metal plate with a (SC density of -3.0 C/M) Find...
  46. H

    Electrostatics of conductors

    "In a static situation, the electric field of a conductor can have no component parallel to the surface coz this would violate the condition that the charges on the surface are at rest." would this statement be valid for electric field at the surface of an insulator? Explain your answer...
  47. Peeter

    Fourier transform solution to electrostatics Poisson equation?

    Am just playing around, and following examples of Fourier transform solutions of the heat equation, tried the same thing for the electrostatics Poisson equation \nabla^2 \phi &= -\rho/\epsilon_0 \\ With Fourier transform pairs \begin{align*} \hat{f}(\mathbf{k}) &= \frac{1}{(\sqrt{2\pi})^3}...
  48. 9

    Charging by Contact: Calculating Charge on a Sphere after Multiple Contacts

    Electrostatics question, need help urgent! Homework Statement A small metal sphere carrying a charge of -2Q is first brought into contact with sphere R Which has a charge of +Q, and then into contact with sphere S which has a charge of +2Q, and finally into contact with sphere T which has a...
  49. S

    Coulomb's Law - Electrostatics

    Hey. I only just started this unit at school (after coming back from holidays and forgetting everything!) and I'm having trouble with the following problem: Homework Statement "Four point charges A, B, C and D are arranged on the corners of a square of side 25cm. If A and B each have...
  50. A

    One-dimensional lattice (electrostatics)

    Homework Statement Hey guys. So, I got this question in the pic. First of all, I drew what I think to be a one-dimensional lattice (in the green box) but I'm not sure, is it right? Second of all, I don't really understand the question, I mean I know that a potential energy of charge q is...
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