What is Electro static: Definition and 46 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. Silver2007

    Magnetic field due to electric wire

    In my opinion, the magnetic field at point P should cancel each other, because the magnetic field caused by the two wires has the same direction, like this. but the solution does not assume that the magnetic fields cancel each other out. I don't know where I'm wrong, please help me, thanks.
  2. M

    Engineering Current density calculation in anisotropic ferromagnetic film

    Hi everyone! First time posting here, so I apologize in advance for any bad formatting. I am working on a mathematical model of an anisotropic magnetoresistive sensor. The central part of such a device is a Wheatstone bridge that consists of four current-carrying ferromagnetic (FM) films, the...
  3. 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.
  4. Harikesh_33

    I Question regarding Laplace's Equation for regions with charges

    Why doesn't the **Laplace's equation**(#\nabla^2V=0#) hold in the region within the sphere when there is a charge inside it ? Is it because #ρ \ne 0# within the sphere and it becomes a **poisson equation**($\nabla^2V=\dfrac{-ρ}{ε_0}$) and changes the characteristics of **Harmonic Solution**...
  5. 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...
  6. H

    Bound charges of a block (top and bottom surface)

    From what I think, to find the bound charges of a block on the top and bottom surface I have to find the electric field or the displacement (D). However, I'm not sure how to proceed with a cube. For example, with a sphere ##E = \frac{Q}{4\pi \epsilon_0 r^2}## since r is constant. For a cube, it...
  7. H

    The polarization charge density ##\rho##p in a charged dialectric

    Hi, I have a dialectric cube and inside the center of the cube I have a part where we have Introduced evenly electrons. I have to find the polarization charge density in the 3 regions. I know outside the cube is the vacuum, thus ##\vec{P} = 0## and inside the dialectric (non charged part)...
  8. H

    Show that ##\int \frac{d\vec{a}}{d} = \frac{4}{3}\pi \vec{r}##

    Hey! I have to show that the integral of the area of a sphere ##\int \frac{d\vec{a}}{d} = \frac{4}{3}\pi \vec{r}##, with ##d = |\vec{r} - \vec{R}|## and ##\vec{r} = r \hat{z}## This is what I did. ##d\vec{a} = R^2sin\theta d\theta d\phi \hat{r}##, ##\hat{r} = sin \theta cos \phi \hat{x} + sin...
  9. rudransh verma

    Studying Regarding learning from Griffiths

    I am a undergraduate student and have done some studying from Resnik book (principles of physics). I have also got Feynman lectures vol1 which I am planning to study with Resnik. I think it will give me a solid grasp on theory. I am getting bored now after doing some chapters from...
  10. rudransh verma

    B Why Are Electric Fields Perpendicular on a Charged Conductor's Surface?

    If there is a spherical conductor like this with excess charges on its surface then this is the field it sets up. Each e- would have there own radial field of lines. And all the e-s would exert a force on each charge and the net field on each charge and thus net force would be zero. All the e-s...
  11. bboo123

    I Exploring the Impact of Dielectrics on Electric Flux Density

    In the 7th edition of the book "Elements of Electromagnetics by Matthew N. O. Sadiku" On page 190 the author goes on to say: "We now consider the case in which the dielectric region contains free charge. If ##\rho_v## is the volume density of free charge, the total volume charge density...
  12. rudransh verma

    I What is Electric Flux and How is it Calculated?

    Gauss law relates between E at some point on guassian surface with the net charge enclosed by that surface. Using gauss law is like being able to tell what (ie charge)is inside a gift box by just looking at the wrapper(electric field). There are two types of problem. Sometimes we know the charge...
  13. jiajie

    Finding the capacitance of two separated hemispheres

    like the picture, two adjacent hemispheres(radius R, distance d, assume the charge is ±Q of each side(assume evenly distributed), can we calculate its capacitance?
  14. Narayanan KR

    At least One Faraday Tube Between Every Two Unlike Charges in the Universe

    By Classic Coulomb's Law there exists negligible yet non zero force of attraction between two unlike charges in-spite of the distance. However for electrostatic attraction to work we need at-least one Faraday Tube(Lines of Forces) between the attracting charges, does that means...
  15. Z

    Boundary Value and Separation of Variables.

    If the boundary condition is not provided in the form of electric potential, how do we solve such problem? In this case, I want to use ##V = - \int \vec{E} \cdot{d\vec{l}}##, but I don't know how to choose an appropriate reference point.
  16. Z

    Question about the classic Image Problem

    I am studying the classic image problem (griffins, p. 124) Suppose a point charge ##q## is held a distance ##d## above an infinite grounded conducting plane. Question: What is the potential in the region above the plane? boundary conditions: 1. V = 0 when z = 0 (since the conducting plane is...
  17. Data Base Erased

    Electrostatic energy of concentric shells

    I know the energy is ##\frac{q²}{ 8 \pi \epsilon_{0}}( \frac{1}{a} - \frac{1}{b})##, but I can't get this result using the second equation. What I did: ##W = \frac{1}{2} \int \rho V d \tau ## ##\rho = \frac{q}{ \frac{4}{3} \pi r³}, a < r < b ## ##V = \frac{q}{4 \pi \epsilon_{0} r}## ## W =...
  18. O

    How to create a uniformly charged sphere?

    Can we create at least any one of the following in laboratory? How? 1. A uniformly charged spherical shell of finite thickness 2. A uniformly charged sphere 3. A radially symmetrically charged spherical shell of finite thickness 4. A radially symmetrically charged sphere
  19. Z

    Electric field direction on a grounded conducting sphere

    I am required to find the direction of the electric field on the surface of a grounded conducting sphere in the proximity of a point charge ##+q##. The distance between the center of the sphere and the point charge is ##d## and using the method of images we find that the charge of the sphere is...
  20. torito_verdejo

    Electrostatics: sign of the potential

    The final result will only differ in its sign, but this is crucial. Having a positively, radially oriented electric field ##\textbf{E}##, I understand that the sign of the integral should be positive (## - (- A) = A##), but it is not! How and why is this the case? A line integral where the...
  21. navneet9431

    The Effect of Conductors on Electric Field Lines

    What is true is that the field due to the point charge outside of the conductor will not be able to penetrate the shell i.e. there will be no field due to the external point charge anywhere within the conductor nor in the cavity: the field will be **killed off*& by the charges on the outer...
  22. Hawkingo

    Why there is a negative sign in the formula of calculating work done?

    $$W = - \int _ { a } ^ { b } \vec { F } \cdot d \vec { r }$$ ( The Force here is referring to the applied force, When moving a positive charge towards another positive charge(stationary) / field In this formula why there is a negative sign in the formula? I am not asking the sign of the total...
  23. Mutatis

    Find the electric field at an arbitrary point

    Homework Statement A distribution of charge with spherical symmetry has volumetric density given by: $$ \rho(r) = \rho_0 e^{ \frac {-r} {a} }, \left( 0 \leq r < \infty \right); $$ where ##\rho_0## and ##a## is constant. a) Find the total charge b) Find ##\vec E## in an arbitrary point...
  24. C

    Floating potential of a conductor in an electrical field

    I'm interested in the following general question: Assume x,y,z is an axes system, and that the y-z plane is occupied by a conductive plate at a known potential V with respect to the earth. Now, a conductive material M of neutral global electrical charge is placed at some distance of the plate...
  25. A

    Confusion with constant voltage and dielectric

    Homework Statement Consider a conducting sphere with radius ##R## connected to a voltage source of ##V_0## volts. If the sphere is then covered by a dielectric spherical layer of radius ##9R## calculated the relative permitivitty ##\varepsilon_0## needed so that the field in the empty zone...
  26. Manolisjam

    Non-conductve sphere with cavity -- find Electric field

    I have a non conducting sphere with a charge ρ=A/r per uni vollume A is constant. suppose there is a cavity in the centre and within a particle of charge q. i want to find the E inside the sphere in respect with r. Homework EquationsThe Attempt at a Solution for radius equal of the cavity i get...
  27. L

    Three parallel plates -- find the electric field

    Homework Statement Find the field at A. Homework Equations ##\oint E\cdot dA = Q_{enclosed}/\epsilon_0## The Attempt at a Solution My first intuition was to do a Gaussian cylinder from A to the middle of the bottom plate. My logic is that the field inside the bottom plate is 0, so I'd have...
  28. Marcus95

    Finding Total Charge from E-field

    Homework Statement A static charge distribution has a radial electric field of magnitude ##E = \alpha \frac{e^{-\lambda r}}{r} ## where λ and α are positive constants. Calculate the total charge of the distribution. Homework Equations Gauss's law ##Q/\epsilon_0 = \int \vec{E} \cdot d\vec{S}##...
  29. Alettix

    Capacitor filled with two conducting materials

    Homework Statement a) State the boundary conditions for the electric field strength E and electric flux density D at a planar interface separating two media with dielectric constants ε1 and ε2. b) A parallel plate capacitor with a plate separation d is filled with two layers of different...
  30. VSayantan

    Electrostatics, Neutral Points

    Statement Four point charges, Q, -Q, Q, -Q, are placed at the four ends of a horizontal square of side a as shown in the figure above. What are the neutral points? The attempt at a solution The square is not exactly aligned parallel in its plane, say XY. So, the center is not a neutral point...
  31. G

    Electric field due to semi-circular wire at a distance

    Homework Statement A semi-circular wire containing a total charge Q which is uniformly distribute over the wire in the x-y plane. the semi-circle has a radius a and the origin is the center of the circle. Now I want to calculate the electric field at a point located on at distance h on the...
  32. S

    Correction to the field energy due to the existence of discrete charges

    In the classical electromagnetic field theory, the field density of energy is given by: $$u = (\epsilon/2)E^2 + (\mu/2)H^2$$ One of the differences between the classical electromagnetic theory and the real world is that in classical EM all charge and current density, (ρ(r), J(r)), is...
  33. Turbotanten

    Find the ionization energy of a simple model atom

    1. Homework Statement A simple model atom is composed of a point-like nucleus with charge ##+Q## and an electron charge distribution $$ \rho(\vec{r})=-\dfrac{\left|Q\right|}{\pi a^2 r}exp(-2r/a) $$ where ##a## is a constant. Show that the ionization energy (the energy to remove the electron to...
  34. Marcus95

    Change in electrostatic energy on two spheres

    Homework Statement We have a spehere of radius ##r_1## and on of ##r_2## far away from each other. The first sphere has a charge ##Q##. What is the change in electro static energy when they are connected together? Homework Equations Potential of a charged sphere: ## V = \frac{Q}{4\pi\epsilon_0...
  35. NicolasPan

    Find the electric field of a uniformly polarized sphere

    Homework Statement We want to calculate the field of a uniformly polarized sphere of radius=R Homework Equations V(\vec{r}) = \frac{1}{4 \pi\epsilon_{0}} \oint_{S} \frac{\sigma_{b}}{r} da' + \int_{V} \frac{\rho_{b}}{r} d\tau' The Attempt at a Solution i)I know that \sigma_{b} = P...
  36. Narayanan KR

    What is the estimated conductivity of Earth according to the USGS?

    1. In above image an insulated metal plate has been placed inside Earth (soil), and an voltage is applied between plate and Earth groung what will be the capacitance here?? 2. one plate is the metal and the other plate is entire earth, so it is a big assymetrical Capacitor or What? all...
  37. V

    A Problem In Electromagnetic Phenomena

    Homework Statement [/B] In a thin rectangular metallic strip a constant current I flows along the positive x-direction, as shown in the figure. The length, width and thickness of the strip are l,w and d, respectively. A uniform magnetic field B is applied on the strip along the positive...
  38. A

    Heat energy from a charged configuration

    Homework Statement [/B] I have two spherical metallic shells with radius ##3a## and ##a##, the little one is placed inside the larger so that the center of the little one is at a distance of ##a## from the center of the larger. The outer one has a charge ##3Q## and the one inside has a charge...
  39. annoyingdude666

    Why infinite conducting rod - Gauss's Law , uses lambda?

    hi, i still don't understand why infinite thin-walled cylindrical shell or conducting rod use lambda rather than sigma ? lambda = C/m ,,, sigma = C/m^2 i mean when we look at conducting rod, the charges inside the conductor is zero, so the charges spread on the surface of conducting rod(have...
  40. P

    Electrical Potential Energy of three quark system

    Homework Statement A proton is composed of three quarks: two "up" quarks, each having charge +2e/3, and one "down" quark, having charge -e/3. Suppose that the three quarks are equidistant from one another. Take the distance to be 3×10-15 m and calculate the potential energy of the subsystem of...
  41. Gh778

    Does this device give a magnetic field?

    Hello, It's a theoretical question. I take 2 electrostatic particules fixed in a circle. I turn the circle. Is there a magnetic field ? I suppose the angular velocity very high and I suppose the particules are fixed in the circle. The diameter of the circle is very small. I don't want the...
  42. marcophys

    Create a dust attracting piece of paper

    I'm looking at equipment that scans an image through a feeder... evidently dust build up could be a problem. Thinking of a piece of paper, that might attract dust, that could be run through it (I saw a vid of a piece of cleaning paper run through a system - I'm presuming it is 'dust...
  43. O

    Trying to compute electro static field

    Homework Statement i tried to compute the electrostatic field of a charged ring at a point not in the center i have problem with transforming from xy to polar system what do you think about this try? Homework Equations The Attempt at a Solution
  44. J

    Can a Third Charge Achieve Zero Potential Between Two Unequal Charges?

    Homework Statement If you bring 2 charges, Q_1 (=+6 micro Coulombs) and Q_2 (= -2 micro Coulombs), from infinity to positions on the x-axis of x = -4 cm and 4 cm, respectively, is it possible to bring a 3rd charge Q_3 ( = +3 micro Coulombs) from infinity to a point on the x-axis between the...
  45. W

    Links Between Electromagnetic, Electro Static and Gravitational Fields?

    When Studying the properties of matter, I came across the properties of Gravity, electromagnetism and electro static fields I'm Wondering: As Gravity and Magnetic Fields a alike and some formulas for finding out the gravity are the same could the three have the same properties. (I have not...
  46. L

    How do electrostatic forces follow the principle of superposition?

    about electro static waves what is meant by the statement that "electro static waves follow the principle of super position"