What is Electrostatics: Definition and 679 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. P

    A question in Electrostatics

    the question is about the uniqueness theorem (right now I am reading in griffiths book). the first uniqueness theorem state's that "the solution to laplace's equation in some volume is uniquely determined if the potential is specified on the boundary surface ". I understand that this gives us...
  2. C

    Gauss' law electrostatics problem involving charge densities

    Homework Statement A nonconducting spherical shell has a thickness b-a, where b is the outer radius and a the inner radius has a volume charge density \rho=\frac{A}{r}, r\in[a,b]. If there is a charge +q located at the center, what must A be in order for the electric field to be uniform in the...
  3. J

    Electrostatics - hollow charged sphere

    So we have a cross sectoin of a sphere that is charged with Q (refer to attachment). electrostatics say the electric field within a charged conductor is 0, and the electric field is perpendicular to the surface. But for a hollow charged sphere (like in the attachment), does the hollow area...
  4. abhishek99087

    Help with an electrostatics problem

    question: A positive charge exists in free space.Now, the charge is enclosed by a spherical shell of finite thickness.What effect does it have on the field lines emanating from the charge...
  5. O

    Electrostatics problem - accelerations of charged beads

    Electrostatics problem -- accelerations of charged beads Hi everyone Im reworking my MP homework and I can't seem to get the right answer for this problem(26.32). The set up says: A 1.5g plastic bead charged to -3.9nC and a 3.8g glass bead charged to 17.6nC are 2.2 cm apart(center to...
  6. C

    Magnitude of Force of two point charges on a third (electrostatics)

    Two point charges are placed on the x-axis as follows: charge q1 = 4.01nC is located at x= 0.201m , and charge q2 = 5.00nC is at x= -0.301m. What is the magnitude of the total force exerted by these two charges on a negative point charge q3 = -6.03nC that is placed at the origin? I know I...
  7. G

    Electrostatics: Equilibrium distance & Acceleration

    Homework Statement As indicated in the diagram, consider a rail inclined at an angle θ relative to the horizontal axis. A sphere (A) with a charge +q is fixed at the bottom of the rail. A second sphere (B) with a charge +2q and a mass (m) is free to move along the rail. The sphere (C)...
  8. V

    Choice of reference potential in electrostatics

    Homework Statement While solving problems in electrostatics we assign zero of potential to infinity .But we also assign zero to ground as well. Now there are electrostatics problems where we use both ground and infinity as zero potential .How is that we have two zero potentials within a same...
  9. T

    Electrostatics net force question

    Homework Statement I am having a problem with 8.4. I get an answer but it does not match the answer in the memo which I think is wrong. Homework Equations The Attempt at a Solution 8.1) T to P (Could someone explain why?) 8.2) Q = (3*10^-9)-(6*10^-9)/2 = -1.5*10^-9 (This is...
  10. Z

    Electrostatics- spheres leaking charge

    Electrostatics-- spheres leaking charge Homework Statement Two small equally charged spheres, each of mass m, are suspended from the same point by silk threads of length d. The distance between the spheres x << d. Find the rate dq / dt with which the charge leaks off each sphere if their...
  11. I

    Electric field Vector The Hub Of Electrostatics 1

    Hey I cought out a pattern in Electrostatics and i created it in my revision notes. I have uploaded it please Suggest if any correction required
  12. M

    Curl of the Polarization (Electrostatics)

    I've been reading Griffith's "Introduction to Electrodynamics" and I've got to this part where it says: "When you are asked to compute the electric displacement, first look for symmetry. If the problem exhibits spherical, cylindrical, or plane symmetry, then you can get \vec{D}directly from...
  13. B

    Electrostatics & Quadric Surfaces

    Hey guys, I'm in some serious trouble - I don't know how to solve a lot of problems in electrostatics. The main reason is that once I seen that you had to be able to find electric fields & electric potentials due to charge distributions on quadric surfaces I panicked & gave up - I was still...
  14. C

    Electrostatics - Metal Shell Question

    Homework Statement Consider a thick metal shell with inner radius a = 2cm and b = 4cm. The shell carries no net charge. A point charge of q = 3nC is placed at the centre of the shell. Find the total charged induced on the inner boundary of the shell. Find the total charge induced on the outer...
  15. B

    Uniformly Charged Circular Sector problem (Electrostatics)

    Homework Statement Hi, I am having problems trying to solve an electrostatics question. Basically there are two circular sectors of radius R and with angle 2β. Both of these sectors have their vertices at the same point in the xy plane (ie at the origin) but have a separation d in the z...
  16. P

    Electrostatics, finding velocity of proton

    1. A moving proton has 6.4 x 10-16 J of kinetic energy. The proton is accelerated by a potential difference of 5 000 V between parallel plates. The proton emerges from the parallel plates with what speed? a) 1.3 x 106 m/s b) 8.8 x 105 m/s c)1.8 x 106 m/s d) 9.8 x 105 m/sHomework Equations...
  17. P

    Electrostatics, finding velocity of electron

    1. An electron orbits the nucleus of an atom with velocity v. If this electron were to orbit the same nucleus with twice the previous orbital radius, its orbital velocity would now be a) \frac{v}{2} b) v c) 2v d) \frac{v}{√2} Homework Equations \DeltaEk + \DeltaEp = 0 ? The Attempt at a...
  18. P

    Electrostatics, parallel plates

    1. A proton with kinetic energy of 2.1 x 10-17 J is moving into a region of charged parallel plates. The proton will be stopped momentarily in what region (attached diagram)? a) Region K b) Region L c) Region N d) Region M Homework Equations \DeltaEk + \DeltaEp = 0 The Attempt at a Solution...
  19. B

    Calculus-based relationships in electrostatics

    Homework Statement I know for example that a=dv/dt and v=dx/dt. I was wondering whether there are similar relationships for things in electrostatics. I have to internalize all of these formulas (for electrostatics), so I was hoping to understand them in a calculus-based sense in order to...
  20. U

    Prove this result Electrostatics

    Homework Statement A ball of mass m1 and charge q1 is projected at an angle ? in a uniform electric field for some time T. The direction of the velocity of the ball changes by 60° and the magnitude of velocity is reduced to half. After removing this ball second ball of mass m2 and charge q2 is...
  21. I

    Electrostatics and the superposition principle.

    what is the whole concept of the superposition principle?
  22. H

    Calculating Electrostatic Force on a Charged Particle Near a Flat Surface

    Homework Statement A particle of charge +q is a distance r away from a charged flat surface and experiences a force of magnitude F pulling it toward the surface. What is the magnitude of the force exerted on a particle of charge +q that is a distance 2r from the surface? Homework...
  23. P

    What are Some Unresolved Questions in Electrostatics?

    I have a few questions pertaining to some concepts in electrostatics, I'd be grateful if someone would help me out. 1) When we place a positive point charge inside a hollow conducting sphere, at its center, field lines emerge uniformly from the sphere. Okay, easy enough. Now, if we place the...
  24. B

    Work equation for electrostatics and electricity

    I have a question about the equation for work as it pertains to electrostatics and electricity. One book I read says equation for work done by electric field is W=qV, but another book says W=-PE. However, when I try both equations for the following problem I get different answer. Could someone...
  25. D

    Electrostatics in RC\DC Circuits-feedback process

    Hello, I've always had problems conceptualizing the physics behind circuits, and it always felt like information is hidden from me. Lately I've been trying to analyze circuits in the microscopic and electrostatic way, as i think it is crucial for real understanding of circuit concepts. I've...
  26. H

    Electrostatics question, involving mass?

    Homework Statement One electron has a mass of 9.11x10^-31 KG. Find the force 1.0 gram of electrons would exert on another 1.0g of electrons from 1.0 kilometer away F = ? Melectron = 9.11x10^-31 kg --> (0.01kg of electron = 9.11x10^-33 kg) Electron Coloumb = 1.6x10^-19 C (ignoring the negative...
  27. J

    What happens when the angle changes?

    Hey, I can't get through this problem from electrostatics. Here's my attempt ##F=-eE## It travels from point A ##(a,0)## to the point B, given by coordinates ##(2a,d)## For it to travel along that path, the electron needs to travel at an angle ##tan(θ) = d/a## (got the slope from the...
  28. Sunil Simha

    Electrostatics problem: Find charges on the surface of the dielectric

    Homework Statement An arbitrarily-shaped object is given a charge q and is then surrounded by a dielectric of permittivity ε as shown in the figure below Find the charges induced in the inner and outer surface of the dielectric. Homework Equations I'm not sure but Gauss's law may...
  29. U

    Can a charged sheet attract uncharged objects?

    Homework Statement A large conducting sheet M is given a uniform charge density. Two uncharged small metal rods A and B are placed near the sheet on one side. Then a)M attracts A b)M attracts B c)A attracts B d)B attracts A Homework Equations The Attempt at a Solution An...
  30. E

    Electrostatics - probably a standard question

    Q) A solid non-conducting sphere of radius R carries non-uniform charge distribution with charge density ρ = ρs(r/R), where ρs is a constant. Show that (a) the total charge on the sphere is Q = ∏ρsR3, and (b) find the electric field inside the sphere. Now first part (a) is fairly easy, assumed...
  31. E

    Electrostatics - find the work done

    A certain charge 'Q' is to be divided into two parts, q and Q-q. What is the relationship of 'Q' to 'q' if the two parts, placed at a given distance 'r' apart, are to have maximum Coulombic repulsion? What is the work done in reducing the distance between them to half its value? It went easy...
  32. diegzumillo

    Electrostatics - method of conformal mapping (from Landau)

    I'm studying Landau's Electordynamics of continuous media and, although I like how succinct it is, sometimes it is too succinct! I'm having trouble with a particular passage, so I'll just try to summarize the section up until the part I don't understand. The topic at hand is electrostatic field...
  33. C

    Boit's experiment on electrostatics

    Hello. On the web address http://etc.usf.edu/clipart/35600/35631/boit_35631.htm there is an apparatus allegedly used by a scientist named Boit. However, I can find no reference elsewhere on the web regarding any scientist with such a name, or even to such experiment. Can someone tell me who was...
  34. J

    Electrostatics not on the same axis

    Homework Statement https://docs.google.com/viewer?pid=sites&srcid=ZGVmYXVsdGRvbWFpbnxtcnRyYXNrc3BoeXNpY3N8Z3g6NzBjNzQxNzIzNDM4Y2M4MQ&docid=236f6ec6993ab970f48b7263eadc4898%7Ca7825efe08310846ea2fbce00fd8bb0b&a=bi&pagenumber=14&w=791 #39. Homework Equations Ep=KQ1Q2/R The...
  35. P

    Electrostatics, capacitor question

    1. Probably a stupid question, but what are the +'s? Are they just representing the fact that there is a lack of electrons on that plate, or are those actually some positively charged particles that rearrange themselves like that? 2. Do they actually rearrange themselves like that? Does the...
  36. Sunil Simha

    Electrostatics problem with pith balls hung using threads

    Homework Statement Please open the attachment for the question Homework Equations 1)coulomb's law The Attempt at a Solution I'm at a loss regarding what to do. Upon reading the question (ignoring the figure), I assumed that the charges will form a square and thus the angle between...
  37. fluidistic

    Div D, div E. What rho is it. (electrostatics)

    I know that the D field has to do with free charges. So when we write Maxwell's equation ##\vec \nabla \cdot \vec D = \rho## we mean rho as the free charge density which does not include the bound charges also known as polarized charges. I know that the E field has to do with both the free...
  38. fluidistic

    Neumann's problem, electrostatics, proof

    Homework Statement In the Neumann's problem ##\begin{cases} \triangle \Phi =-4\pi \rho \\ \frac{\partial \Phi }{\partial n}=g \end{cases}##, what condition must g satisfy?Homework Equations I'm given the answer, it's ##\int _ \Omega \rho dV=-\int _{\partial \Omega } g dS##.The Attempt at a...
  39. J

    A second order nonlinear ode in an electrostatics problem

    I encountered the following second order nonlinear ODE while solving a problem in electrostatics. The ODE is: \frac{d^{2}V}{dx^{2}} = CV^{-1/2} How can I solve this? Regards. Homework Statement Homework Equations The Attempt at a Solution
  40. P

    Electrostatics and Coulumb's law, potentials and test charges

    I am given 4 potential charges, 1V, 3V, -6V, and 5V, all arranged randomly around each other. There is a test charge located at infinity. No distances are given between the potentials.1. Where will a test charge of 2*10^-6 C travel? 2. What is its kinetic energy? 3. Find the capatinance of a...
  41. D

    Equation for speed of charges (electrostatics)?

    I am trying to do an exercise but there's no equation in the book that links speed and charges. Can anyone help? This is the exercise: Homework Statement There is a particle with mass = 20 grams and charge = 6 x 10^(-6) C, and another particle with mass = 50 grams and charge = -4 x 10^(-6) C...
  42. M

    Taylor expansion of an electrostatics problem

    Homework Statement The problem has six charges that are at the corners of a regular hexagon in the xy plane, each charge a distance a from the origin. I have already solved for the electric fields in the x and y direction and now am trying to apply an approximation for the field on the x-axis...
  43. A

    Earnshaw's Theorem and electrostatics

    Homework Statement 14: a: It is impossible to have a stable equilibrium in electrostatics. This idea is known as Earnshaw’s Theorem. Let’s prove this fact. Assume that at a particular point P that a charge Q is in a stable equilibrium. Think about the direction of E⃗ necessary for the...
  44. D

    PN junction: basic electrostatics

    Hi, I'm stuck with the electrostatics of the PN junction. I just can't see why the electric field has to be negative in the depletion regio. The two equations give positive values for the Electric field in the intervals, so how can it be negative?? In the equation for the n regio, there are...
  45. V

    A thought experiment on relativistic Electrostatics

    Here is a thought experiment on Special Relativity involving charges which are rest with respect to each other. Consider a configuration of charges as shown in the image. Four identical charges (q) are placed at the corners of a square with an opposite charge at the centre (Q). The value of...
  46. 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)...
  47. 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...
  48. 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...
  49. 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...
  50. 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}...
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