# Tagged Questions

Electrostatics is concerned with the electrical fields and scalar potentials of stationary electrical charges and charge distributions. Use this for questions about electromagnetic situations in which currents and magnetic fields are absent, otherwise use [tag:electromagnetism] and/or [tag:magnetic-...

213 views

### Two charged spheres connected with a conductor

I have a problem with a electrostatics problem: there are two spheres, each one of the same size carrying the same amount of charge, but of different sign. They are connected by a conducting wire, ...
303 views

### electric charges of metals in electrostatics

In electrostatics does metal gain electrons to be an ion or it conduct electrons in form of gaining them to have a negative electric charge
725 views

### Force per unit length between two long parallel wires, one of which is insulated

Suppose we have two very long parallel wires of radius $a$ and distance between their axes $d$ ($d>>a$). The first wire if is carrying charge of linear charge density $\alpha$ and is insulated ...
45 views

Given $N$ equally charged points lying on the unit sphere ("electrons"), the Thomson problem consists of finding the configuration of these points such that the electrostatic potential energy $$U=... 4answers 671 views ### How would you define electrostatics and magnetostatics starting from Maxwell's equations? I'm reading Griffith's text, and he starts by defining Electrostatics as requiring the source charges don't move. I've seen a few slightly different definitions of electrostatics and magnetostatics. ... 1answer 80 views ### Disturbing a line of infinite alternating charges Consider a line of infinite number of alternating charges. All are point charges having charge of same magnitude and are placed in a line. Neglect the effect of gravity here. Consider one of the ... 1answer 182 views ### Finding the potential between two spherical shells [closed] How to find the potential in region a<r<b I know that the general solution for Laplace's equation is$$V(r,\theta)=\sum_{l=0} \left[A_l r^l +\frac{B_l}{r^{l+1}} \right]P_l(\cos{\theta}).$$... 1answer 51 views ### Why an undoped heterojunction causes potential barrier? In this image (source) a potential double-barrier was created using GaAs and AlAs lattices (undoped). Why would any potential barrier be formed, if all the bonds are electrostatically balanced (i.e. ... 1answer 120 views ### Charge density on a plate of a realistic capacitor Suppose we have a realistic capacitor,connected to a constant voltage source, with plates at some distance d and a varying charge density across plate due to edge effects. Is it correct to assume ... 1answer 3k views ### Capacitance of two non parallel plates What is the formula for capacitance of two non parallel plates at an angle with each other?If the plates were parallel then the value can be calculated as (PermittivityX area of one plate)/distance ... 1answer 287 views ### Want to know about divergence [duplicate] Can anyone please explain how to know whether a vector field has divergence or not by seeing its diagram? I have read that a vector field must change for having divergence but why is divergence zero ... 6answers 730 views ### What keeps electrons on a negatively-charged conductor from leaving? Imagine a negatively charged conductor in a vacuum. The excess electrons will be spread out over the surface such that the net electric field inside the conductor is zero. What keeps these extra ... 1answer 945 views ### Energy of a charge inside spherical conducting shell A point charge q is at the center of an uncharged conducting spherical shell of finite thickness, with inner and outer radii a and b respectively. Find the work done on the system when q is ... 1answer 227 views ### Electric Potential-can anyone give the concept behind this? Three points A, B and C lie in a uniform electric field (E) of 5 x 103 NC-1 as shown in the figure. Find the potential difference between A and C. I think there is some trick? How can the pd ... 1answer 19 views ### Electrostatic Potential-I tried many times ,but failed A positive charge Q is placed at point O. Is the potential difference (Va-Vb) positive,negative,or zero,if Q is (i)positive,(ii)negative? Can anyone give the concept behind this? 3answers 199 views ### Is the charge distribution for an electric field unique? If the electric field and boundary conditions are known exactly for a region of space, is it true that there exists only one charge distribution in that region of space that could have produced it? ... 1answer 102 views ### Derivation of a work done by forces on charge Feynman claims is his lectures the following statement: Suppose we have two charges q_1 and q_2 separated by the distance r_{12}. There is some energy in the system, because a certain ... 2answers 315 views ### How does the force between two charges becomes zero? In case of Coulombs law,$$ F=k\frac{q_1q_2}{d^2} $$So, if F=0, then q_1q_2 must be 0. Is this true? 1answer 171 views ### Laplace equation vs Gauss theorem Two concentric conducting spherical shells of radii a_1 and a_2 (a_2>a_1), are charged to potentials φ_1 and φ_2, respectively. Determine the electric potential and field in the ... 1answer 123 views ### Usage of Poisson's equation? I revisited electrostatics and I am now wondering what the big fuzz about Poisson's equation$$\nabla^2 \phi = -\frac{\rho}{\varepsilon_0}$$is. Wiki says One of the cornerstones of electrostatics ... 1answer 25 views ### How does the dieletric displacement change among two dieletric materials? Here's a question I am working on. "A sphere of linear dielectric material with permittivity \epsilon_1 and radius a is surrounded by an infinite region of linear permittivity \epsilon_2. In the ... 1answer 293 views ### Flashing a fluorescent light bulb with high voltage My son and I built a Wimshurst machine (our second try) over the last couple of weekends. It works -- not terribly well, as it only makes 2cm sparks with 20 cm disks (something like 60 kVolt when it ... 0answers 22 views ### electrostatic force vs gravitational force [duplicate] I have question regarding the forces caused by electrostatic charges and gravity. From the explanation here in the link just by existing an object with mass distorts space-time. Will there be a ... 1answer 63 views ### Finding energy stored in a capacitor i am given a voltage time graph for a capacitor circuit. How to find energy stored in that capacitor at various time instants? Can we just calculate by using \frac{1}{2}CV^2 We are given capacitance ... 2answers 158 views ### Relation between electric field and dipole moment I want to show the following equality$$\int_{\left|\vec{r}\right|<R}d^3r\vec{E}\left(\vec{r}\right)=-\frac{\vec{p}}{3\epsilon_0}$$where \vec{p} is the dipole moment of a charge distribution \... 1answer 226 views ### How is the electostatic field propagated by the vacuum? How does a charge feel the presence of another charge when there is NOTHING between them? Is the word "vacuum" equal to "nothing"? Imagine two charges of opposite sign, far from one another in vacuum, and moving with constant velocity - s.t. none radiates energy, none emits photons. At ... 3answers 1k views ### Polarization vector of dielectric electrostatics I know two laws for Polarization vector of a dielectric material$$\vec P = N q \vec{\Delta L}$$Where N is the number of dipoles per meter cube, \vec{\Delta L} is the vector that represents the ... 4answers 176 views ### Electrostatics and two electric charges [closed] How can two identical metallic objects have the same but opposite charges (one loses electrons and one gains electrons) when we know that metals have the ability to lose electrons only? 1answer 243 views ### Charge distribution on a doughnut shaped conductor In a spherical solid conductor the charge is always on the outer surface. Even if the sphere has a cavity, the surface of the inner cavity can not carry a charge due to Gauss's Law. What would be ... 3answers 536 views ### Explaining the current flow of the positive shunt clipper (diodes) I am currently studying clippers or parallel limiters in the Navy and I was wondering if someone could clear up a few things for me. Here is a picture that fits my description: A clipper has a ... 1answer 57 views ### Tranverse electromagnetic waves TEM waves do not exist in waveguide. Is this the correct explanation- Both curl and divergence of TEM are zero inside the waveguide and because of the boundary conditions (electric field zero at every ... 1answer 2k views ### What is the force between two charged objects when the space between them is partially filled by a dielectric medium? I am given two charged particles of same charge at a distance of r. They initially apply force F. Now an infinite dielectric (of dielectric constant 4) of width \frac{r}{2} is introduced ... 1answer 65 views ### What are the consequences of connecting a non-ideal conductor to a battery in open loop? Suppose I have a battery with \Delta V=5[\mathrm{V}]. Now I connect a piece of a metal wire to the "+" side of the battery only. Let's assume that the ambient air is not conductive at all: Are ... 3answers 544 views ### Why capacitance is given as constant value in Farads, and not as max charge in Coulombs? The equation for capacitance is Q=CV or V={1\over C}Q. I don't understand what is the physical meaning of this "C": Does the charge in a system changes linearly with voltage under all ... 1answer 1k views ### Why does energy rise in a constant voltage capacitor after inserting a dielectric? For example from this link: http://te.fisica.edu.uy/fuerza_en_Capacitor.pdf we can deduce, that the work the electric field inside a constant-voltage capacitor does during the insertion of a ... 1answer 78 views ### Find quantity of electricity of two circular faces So, there are two circular conductive sheets with quantities of electricity of Q and -Q. If I know that the distance d between them is 0.002 meters and their radius is 0.1m and the voltage between ... 2answers 153 views ### Using Coulomb's law to solve for a continuous charge distribution [closed] I have been trying to evaluate this specific integral and have been completely stuck.$$\frac{1}{4\pi \epsilon_0} \int^L_0 \frac{2\lambda z}{(x^2+z^2)^\frac{3}{2}}dx.$$I am a freshman and have been ... 1answer 23 views ### discharging static Quick question, if you have a buildup of static charge causing sheets of paper to stick together, can you have a grounding foil touching the paper to dissipate the charge to prevent pages from ... 0answers 67 views ### Electric field at a point [closed] We consider a thin disk whose center is O and radius is R, which has an electric surface charge density of \sigma. We want to find the expression of the electric field \vec{E} at a point M ... 1answer 126 views ### Electric field and potential between two charges [closed] There are two point charges on the x axis and x' is a place where the potential, relative to infinity, is the biggest. Why is the electric field zero at this point? 0answers 101 views ### Electric field in a “concave” conductor I am aware that the electrons are distributed across charged conductor surface so that the areas with smaller radius of curvature have more charge per surface area. But what happens when the ... 0answers 42 views ### Addition of forces in dielectric material In this paper (page 2 of document) it is said that: Because this calculated force was comparable to the gravitational force, they assumed that the same would be true for the forces on a ... 3answers 628 views ### Calculate the flux of a point charge with Gauss's law I know from my class that to calculate the flux of a point charge with Gauss's law, I have to make a surface that intersects with all of the flux lines resulting from the charge, and then make this ... 1answer 42 views ### Finding voltage between two points in space If electric field vector is defines as : \vec{E} = \frac{V_0x^2}{a^3} \vec{i_x} + \frac{V_0y}{a^2} \vec{i_y}  where V_0  and a are known constants, \vec{i_x} and \vec{i_y} unit vectors of ... 1answer 142 views ### The “classical radius” of the electron [closed] According to one theory, the mass m of the electron arises simply as a consequence of the electrostatic energy of its electric field, through Einstein's famous expression ε=mc^2, where ε is the field ... 1answer 171 views ### Net Electric Field of Multiple Charges [closed] Question: Four charges, each of magnitude +Q are placed at the corners of a square of side a. Obtain an expression for the electric potential at the centre of the square and at the mid point of one ... 1answer 239 views ### How does EM radiation depend on the reference frame? In special relativity, magnetism is electrostatics in a different reference frame. This is how we explain the magnetic field being produced by moving charges (aka currents). Charges that move produce ... 1answer 44 views ### Show the equivalence of two electrostatic energy$$U = \frac{1}{2}\iint_{all space}^{ } \frac{\rho(1)\rho(2)}{4\pi\epsilon_{0}r_{12}}dV_{1}dV_{2} $$and$$U = \frac{\epsilon_{0}}{2}\int_{allspace}^{ } \vec{E} \cdot \vec{E} dV. In the left ...
Imagine I have an electric field $E$ created due to some free charges. Then I introduce a dielectric material somewhere. What confuses me is the polarization field $P$, which is now proportional to ...