Electrostatic Definition and 883 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. KnightTheConqueror

    B Is Newton's third law getting violated here?

    Suppose a charge is moving towards another charge at rest. At a given instant of time, The electrostatic force applied by either charge on the other is same, but only one is applying magnetic force on the other. Doesn't this violate Newton's third law?
  2. BuggyWungos

    Solving for potential using surface charge density of a sphere

    surfafce area = 0.502 E = -q/A2(en) = 3800 -q = 3800*(A2(en)) -q = 1.68*10^(-8) -q = 3.37*10^(-8) V = kq/r V = (9.0*10^9)(-3.37*10^(-8))/0.2 V = -1519 V
  3. tellmesomething

    Please help with this suggested solution involving electrostatic press

    My teacher gave us this idea: He told us that the contact force due to one halve on the other halve and the electrostatic force will balance each other. Therefore they'll be same in magnitude so use the former to get the answer However i do not understand how they will be equal. Intuitively it...
  4. tellmesomething

    Why is the superposition principle valid here?

    This is a discussion for (r<R). Assuming a gaussian surface at x=r from the center we get $$E(r) = \frac{Ze} {4π\epsilon_0} ( \frac{1} {r²} - \frac{r} {R^3} )$$ However we get the same result if we consider a wholly negatively charged solid sphere and find the field at a distance r inside...
  5. P

    I Problem with one of the premises in electrostatic pressure theory

    I have the video linked with the time stamp. . Isn't Electric Field anywhere inside the conductor zero. So there will be no electric field inside the thickness of the conductor. But he managed to integrate it somehow? he considered electric field to be changing inside the conductor that has...
  6. L

    I Work to move a point charge from infinity to the centre of a charge distribution

    Electrostatic potential $$ \Phi(\vec{r})=k \int \mathrm{d}^{3} r \frac{\rho\left(\vec{r}^{\prime}\right)}{\left|\vec{r}-\vec{r}^{\prime}\right|} (i) $$ with $$ k=\frac{1}{4\pi\epsilon_{0}} $$ in SI units. What work is required to move a point charge q from infinity to the center of the through...
  7. Z

    Syntax Error? x and y components of E field in unit vector form

    I am trying to work through the MIT free coursework to study Physics before next semester and I am having a heck of a time with the strict answer syntax, or I am having a fundamental issue with the physics, of course. The problem is from "Week 1: Electrostatics Problem Solving Practice 1 W1PS4...
  8. PhysicsRock

    Dipole moment of given charge distribution

    I have come up with a solution, however, I'm not sure whether I'm correct. A fellow student of mine has a different result. I'm gonna show my solution, and hopefully one of you can confirm my result or tell me what I did wrong. $$ \begin{align} p_z &= \int d^3x z \rho(\vec{x}) \notag \\ &=...
  9. G

    I When to properly use "voltage"

    Hi. I'm confused about the usage of "voltage". Some scripts I read introduce it in electrostatic as potential difference (where there's only the scalar potential), but continue using it when changing magnetic fields are present ("induced voltage"). Others make a clear distinction and introduce...
  10. mangofan

    I Electrostatic force exerted on an electron inside a nucleus

    This is SAMPLE PROBLEM 25-7 from "Physics" by Resnik, Halliday, and Krane, in the chapter "Electric Field and Coulomb's Law". After describing the behavior of uniformly charged spherical shells: follows a sample problem: The solution to (a) goes to say that the volume inside R/2 is 1/8 of the...
  11. V

    Equipotential surface (test questions)

    The answer to the first question should be a sphere since for very large distances the multiple charges will act as a point charge. 1(a) is correct answer. For the second question, I find it slightly vague. How can equipotential surface be zero, may be it's asking for the potential of...
  12. milkism

    Multipole expansions, calculating the various moments of point charges

    Problem: Solution: This was quite simple, are my solutions correct?
  13. milkism

    Method of Images, combination of an infinite plane and a hemisphere

    Problem: I have done part a) in spherical polar coordinates. For part b) I thought it would be just: $$\sigma = -\epsilon_0 \frac{\partial V}{\partial r}$$ But I got confused by "You may want to use different coordinate systems .." So I assume partial derivative w.r.t to r is the spherical...
  14. rokiboxofficial Ref

    Surface density of the charges induced on the bases of the cylinder

    The correct answer to this problem is: ##\sigma = \varepsilon_0E\frac{\varepsilon-1}{\varepsilon}## Here is my attempt to solve it, please tell me what is my mistake? ##E_{in} = E_{out} - E_{ind}## ##E_{ind} = E_{out} - E_{in}## ##E_{in} = \frac{E_{out}}{\varepsilon}## ##E_{ind} = E_{out} -...
  15. V

    Force between point charges at the center of two spherical shells

    If these point charges were placed in vacuum without any spherical shells in the picture, then the force between these charges would be ##F =\dfrac { k q_1 q_2} {d^2}##. But, I am unable to reason how spherical shells would alter the force between them. I do know that if charges were on the...
  16. V

    Discontinuity in an Electric line of force

    This is a tricky and difficult question for me. I know from reading various textbooks that electric lines of force are always continuous without breaks, but cannot pinpoint a reason for this. The only reason I can come up is that an electric line of force must always begin and end on charges...
  17. M

    Electrostatic equilibrium problem

    For this problem, I don't understand why this is impossible. Can someone please help? Many thanks!
  18. cwill53

    Calculation of Electrostatic Potential Given a Volume Charge Density

    Part (a) was simple, after applying $$Q=\int_{\mathbb{R}^3}^{}\rho \, d^3\mathbf{r}$$ I found that the total charge of the configuration was zero. Part (b) is where the difficulties arise for me. I applied $$V(\mathbf{r})=\frac{1}{4\pi \epsilon _0}\int_{\Gamma }^{}\frac{\rho...
  19. R

    Use Gauss' Law to calculate the electrostatic potential for this cylinder

    I solved laplacian equation. and got the solution of V(r, phi) = a. +b.lnr + (summation) an r^n sin(n phi +alpha n ) + (summation) bn r ^-n sin( n phi +beta n)
  20. V

    How does the electroscope lose electrons to the Earth?

    I get step 1, in which due to electrostatic induction the top part of electroscope gets positively charged while the leaves of electroscope become negatively charged. Now if we Earth the positively charged end of electroscope as shown in step 2, then electrons must flow from Earth to...
  21. Ahmed1029

    I Helmholtz's theorem and charge density

    According to Helmholtz’s theorem, if electric charge density goes to to zero as r goes to infinity faster than 1/r^2 I'm able to construct an electrostatic potential function using the usual integral over the source, yet I don't understand how this applies to a chunk of charge in some region of...
  22. T

    A Is Gravity Just the Electrostatic Force?

    I read this paper and this is iindeed a very interesting hypothesis. The implications of this theory if true are enormous! Please comment! Is Gravity Just the Electrostatic Force? <crackpot link deleted>
  23. smiddleton26

    Misc. Expand balloon with static electricity

    The idea is to wrap a balloon in several layers of material, similar to that used in electrostatic adhesion wall climbing robots, and run power through the layers. The electrostatic charge on the layers outside the balloon will build up and the air inside the balloon will begin to become...
  24. Ahmed1029

    I Average electrostatic field over a spherical volume

    this formula in the picture is the average electrostatic field over a spherical volume of radius R. It is the same expression of the electrostatic field, at the (position) of the point charge, of a volume of charge of uniform density whole entire charge is equal to (negative)q. My question is...
  25. Ahmed1029

    I Exact electrostatic potential of a pure dipole using multipole expansion

    If I have a physical dipole with dipole moment p. Now, this formula for potential (V) is a good approximation when r is much larger than both r1 and r2 in the picture below. It's however said that for a pure dipole for which the separation between charges goes to zero and q goes to infinity, the...
  26. V

    B How is capacitor energy the same as electrostatic potential energy?

    The energy stored in a capacitor is derived by integrated the work needed to move charge dQ from one plate to another. I'm confused on how this energy is the same as electrostatic potential energy, the energy needed to assemble this configuration from infinity. In the case of capacitor energy...
  27. C

    I Where to find this uniqueness theorem of electrostatics?

    There is a nice uniqueness theorem of electrostatics, which I have found only after googling hours, and deep inside some academic site, in the lecture notes of Dr Vadim Kaplunovsky: Notice that the important thing here is that only the NET charges on the conductors are specified, not their...
  28. S

    Exploring Electric Field Boundaries at a Charge Density Boundary

    Hey, I have a really short question about electrostatics. The boundary conditions are : \mathbf{E}^{\perp }_{above} - \mathbf{E}^{\perp}_{below} = -\frac{\sigma}{\varepsilon_{0}}\mathbf{\hat{n}} , \mathbf{E}^{\parallel }_{above} = \mathbf{E}^{\parallel}_{below}. My question is what is...
  29. R

    I Electrostatic Influence and Series-Connected Capacitors

    As you know, "in the classics" the charges of the capacitor plates are equal in absolute value and opposite in sign. However, let us consider a series connection of capacitors. In this case, a charge of the opposite sign is induced on every second plate of each capacitor due to electrostatic...
  30. E

    Electrostatic vs DC Conduction Simulations for E-field Analysis

    Hi, I am doing e-field simulations and have came across two types; electrostatic and dc conduction. I know that electrostatic means there is no changing field so I'm just hoping for discussion on when one is more appropriate than the other and when one definitely should or should not be used.
  31. H

    Boundary conditions (E and D) for a dielectric sphere

    Since there is no free charge ##\int_S \vec{D} \cdot d\vec{a} = 0## and ##\rho_f = 0## ##\sigma_f = 0## ##\vec{nabla} \cdot \vec{P} = 0## since P is a constant ##\rho_b = - \vec{nabla} \cdot \vec{P} = 0## For a simple surface we can find the boundary conditions for ##\vec{E}## using a Gauss'...
  32. samy4408

    I Positive Charges: Explaining Motion Despite Net Force = 0

    in a cours of electrostatic when we have a positive charge and we bring another one (also postitive)we have to do work and apply a force that equals the force of repultion over the distance which seems weird because if we do that the net force will be equal to 0 and the charge will not move can...
  33. Hamiltonian

    The Net Electric Field Inside a Dielectric

    The net Electric field(inside the dielectric): $$E_{net} = \frac{1}{4\pi \varepsilon_0 \varepsilon_r} \frac{q}{r^2}$$ $$\vec E_{net} = \vec E_{applied} - \vec p$$ where p is the polarization vector. let charge ##q_{-}## be present on the inner surface of dielectric and ##q_{+}## on the outer...
  34. V

    Force acting on a charge across a hybrid medium

    The force on charge ##q_2## will depend on the electric field in medium with dielectric ##K_2##. Electric field in this second dielectric due to ##q_1## is ##E = \dfrac {kq_1} {K_2r^2}## where r would be the distance from ##q_1##. So, the electric field at the point where charge ##q_2## is...
  35. mohammed

    Solving Electric Field Vector Problems Using Gauss's Law

    I'm preparing for exam but it seems I can't find problems similar to this on the internet. Here I will apply Gauss's law on the electric field vector to get the charge density. but the problem is that I can't find similar examples on the internet that uses direct vectors on Maxwell's equations...
  36. Ugnius

    Electrostatic potential and electric field of three charges

    So I started with b) and it there was no q2 this would seem reasonable I was wanted to ask , what effect does q2 have on potential of these two charges? Because it has to be given for a reason.
  37. A

    Unstable or stable electrostatic equilibrium?

    I wonder if you could help me with both I'm stuck, I know that in order to see if the electrostatic equilibrium is stable or not at the center of the ring , the potential energy has to be minimum there. I was going to use Laplace eq. but it allows neither minimum nor maximum. Then I also...
  38. Anonymous243

    Electrostatic potential energy of a non-uniformly charged sphere

    Hi, I'm new here, so I don't know how to write mathematical equations, and I may not be fully aware of the rules here, so I'm sorry if I made a mistake. I know how to calculate the electrostatic potential energy of a countable number of charged particles, but I don't know how to calculate the...
  39. A

    Electrodynamics: electrostatic potential

    Hi! I tried to solve it by using the equation of the electric potential above and as we see it requires the electric field, but the electric field at the center of the ring is zero. Then I tried by using the equation [text] V = \frac{1}{4\pi\epsilon_0r} \int \lamda dl [\text] and I got [text] V...
  40. Gustav

    Electrodynamics, Electrostatic potential, electric-field

    I am unsure how to solve the problem and would appreciate any suggestens on how to start solving the problem.
  41. V

    Dipole placed in a uniform electric field

    My understanding is that the uniform electric field ##\vec E## cannot be the net electric field since the dipole creates its own electric field as shown in first diagram below, which must superimpose with the uniform electric field. So, yes, the uniform electric field ##\vec E## around the...
  42. nazmulhasanshipon

    Comparing energy lost by the battery & energy gained by the capacitor.

    Imagine the two terminal of a *parallel-plate capacitor* are connected to the two terminal of a battery with electric potential difference #V#. If the capacitance of the capacitor is #C#, and the area of each plate is $A$. In this process would the energy lost by the battery and the stored...
  43. A

    B Electrostatic charge build up in environmental electron microscopy

    Hello, If I understand it correctly, the samples are grounded inside a scanning electron microscope (SEM) to avoid charge build up through the electron beam. Also the non-conductive are coated with a conductive layer, so they can be grounded as well. However, I do not know how the charge build...
  44. MichPod

    I Calculating Force & Acceleration in Electrostatic Field (B=0)

    For a case of electrostatic field (B is equal zero), how should the force acting on a moving charge be calculated if we want to take into account all the relativistic effects? Also would it be correct to calculate the acceleration of the charge as a=F/m, or should some other formula be used? For...
  45. V

    Reason for glass rod losing electrons

    I am not sure if the explanation below is enough. This is a high school level question. When rubbing occurs between glass and silk, then heat energy is produced which provides the energy needed to free up electrons in outermost orbits of atoms in silk or glass. But silk has very tightly bound...
  46. jackiepollock

    How to picture a radial field around a 3d object?

    Hello! First off, for a), I am not too sure how to picture a radial field around a 3d object. I know that this spherical metal dome is basically a enlarged version of an atom, but since with problems on radial field around an atom, I don't have to consider its diameter, I'm not sure how the...
  47. jackiepollock

    B Problems regarding electrostatic forces in everyday levitation

    Hello! I'm reading this part of the A-level physics book and finding a few places that I couldn't wrap my head around. They are underlined. 1) When saying oxygen, is it saying that oxygen is the most abundant element in the shoe atoms? 2)I am not too sure why the force per atom is shared...
  48. F

    Kinetic and potential energy of a particle attracted by charged sphere

    Hello, I have a particle at point A with charge ##q_A##, and an unmovable sphere of radius ##R_B## at point B with a volumic charge density ##\rho##. The distance from particle A to the centre of the sphere in B is ##r##. Both objects have opposed charges, so, the particle in A, initially at...
  49. M

    Help with Coulomb's law: Net electrostatic force

    I tried just calculating the force with Coulomb's law, then calculating the forces for each vector individually and adding, but I got it wrong both ways
  50. A

    Capacitance of a parallel-plate Capacitor with non uniform dielectric

    Hey guys! I'm having trouble with the solution that I arrived at. Through boundary conditions I'm able to determine ##\vec{D}## as $$\vec{D}=-\frac{4Q}{R_0^2}\hat{e_z}$$ (In CGS units) Trough that I'm able to get the electric field as $$\vec{E}=-\frac{1}{\epsilon(r)}\frac{4Q}{R_0^2}\hat{e_z}$$...
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