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 ...

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Gauss's law giving incorrect answer

Let's consider two concentric spherical shells, one of radius $R$ and one of radius $R - \Delta R$. The outer shell is negatively charged and the inner shell positively, but both the shells have net ...
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Flux through side of a cube

I am looking at Griffiths introduction to Electrodynamics 3rd ED. Problem 2.10 asks for the flux of $E$ through the right face of the cube, when a charge $q$ is in the back left corner of the cube. ...
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139 views

Electrostatics and two electric charges

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?
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1answer
38 views

Why is it true that Laplace's equation does not hold within the sphere in this case?

Find the average potential over a spherical surface of radius $R$ due to a point charge $q$ located inside. (In this case Laplace's equation does not hold within the sphere) This is a question ...
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Do electric and magnetic lines of force physically exist?

As per my imagination any thing can't impose force on the other by not giving even a touch(i,e action at a distance). So I thought there must be some physical existence of lines of force. Although ...
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58 views

Calculating the amount of work done to assemble a net charge on a sphere

I've been reviewing electrostatics using an old exam and I stumbled upon this question: Calculate the amount of work required to assemble a net charge of $+Q$ on a spherical conductor of radius ...
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1answer
83 views

Distribution of surface charges in an electric circuit

I'm reading Sherwood and Chabay's brilliant textbook Matter and Interactions, in particular the section that deals with how the surface charges in an electric circuit distribute themselves to generate ...
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1answer
166 views

Method of image charge for cylindrical conductor

I am simply puzzled that only for spherical and planar conducting surfaces the method of images is applied. Is it (really) impossible to find image charge or charge distribution which can simulate the ...
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9k views

Why is the electric field perpendicular to every point on the surface of a conductor?

I am reading Berkeley Physics Course, Volume 2 (Electricity and Magnetism by Edward M. Purcell). I am in chapter $3$, page $92$, and the book discusses conductors. The following is from the book: ...
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14 views

Would a previously poled piezoelectric material experience a force aligning it with an external electric field?

I'm wondering if it would possible to crush a poled PZT object, disperse the powder into a thermoplastic (with a melt temperature below the Curie temperature of PZT) and align the 'crystal shards' ...
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1answer
42 views

Electric Field Due To Parallel Charges Metal Plate System At Outside Point [closed]

In parallel metal plate configurations the facing sides of metal plates should have equal and opposite charges.But I came across a problem today on the net like this.In this problem below how ...
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1answer
40 views

Applying Kirchoff voltage law to a short circuit

If you consider an ideal wire with no resistance that shorts an ideal battery, the only voltage drop that exists is the emf of the battery, with nothing to balance it. Obviously in the real world ...
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1answer
43 views

E field of parallel plates with metal inside

I was asked to determine the electric field in the spaces between the copper bar and the plates. The voltage across the plates was 30 V, so naturally I’d use $E=\Delta V/d$ to determine the field. ...
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Description of transparency of a Faraday cage to different frequencies?

A Faraday cage within a static electric field leaves an internal electric field equal to $\vec{0}$ (as long as there are enough mobile electrons in the conductor to counteract the external $\vec{E}$). ...
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34 views

Can a floor made of copper pennies produce a static electric shock?

A friend is going to install thousands of pennies in a mosaic layout to be used as flooring in his home. Can this floor produce a static electric shock when walking on it? Is it possible to ...
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31 views

Screening of electrostatic potential at the interface between two dielectrics

The motivation of my question: Calculating the dispersion relation of plasmons in a graphene layer embedded between two dielectrics with different dielectric constants. Addressing my question: I ...
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28 views

Explanation on Electrostatics

If we rub a plastic scale repeatedly with our dry hair,then the hair stand up and separate from each other. Why does this happen?
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41 views

Ionization of human molecules

Can the molecules human body be positively charged and can the body process the electrons through exercise if retained and not discharged? Example asked by commentator: When you rub your feet on ...
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1answer
68 views

Regarding the proof of Gauss's law

I know that this question has already been asked multiple times but I´m still not getting on the mathematical details behind the answers... So I hope that this question doesn´t get closed. First I ...
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1answer
123 views

Why is the force on the charge at the tip of a cone infinite?

Imagine a charge $q$ that is located at the top of a hollow cone with a surface charge density $\sigma.$ The slant height is $L$ and the charge $q$ sits at the vertex of angle $2\theta$. We are ...
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32 views

Spherical charge distribution [closed]

I have a pretty simple exercise but i can't get it right using both integration and divergence of potential. I first did the field inside the sphere: $$\vec{E} = ...
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4answers
669 views

Why is there an electric field in a wire even though it is a conductor?

If you take a perfect conductor, there cannot be a field across it since if there were, the particles would arrange themselves in a way to cancel out the field right? Yet, why does the same not hold ...
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1answer
120 views

Minima & maxima of Laplace's equation

I don't get the following sentence from David J. Griffiths' Introduction to Electrodynamics (the ambiguous sentence is in bold) Laplace's equation tolerates no local maxima or minima; extreme ...
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0answers
48 views

Laplace equation in parabolic coordinates [closed]

I'm stuck on a seemingly simple 2D electrostatics problem which doesn't allow for straightforward solution by separation of variables: A parabolic interface, with its axis parallel to the $x$ axis, ...
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1answer
59 views

Number of electric field lines and intensity of electric field

I´m currently studying electrostatics and I´m having a hard time understanding why do the number of electric field lines is proportional to the intensity of electric field? I just don´t see it. Can ...
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2answers
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Why two objects get charged by rubbing?

It is always told as a fact without explaining the reason. Why do two objects get charged by rubbing? Why one object get negative charge and other get positive charge?
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Question about Cavendish experiment

I got a question. In Cavendish experiment was used lead in both of spheres. Can we repeat that experiment with balls made from stone or anything else. Because lead could be a byproduct of radioactive ...
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2answers
77 views

Physical meaning of electric dipole moment [closed]

I am reading about the electric dipole moment. What I can't understand, and seems that no one cares to explain, is what is the physical meaning of it. To my understanding everytime that dipoles are ...
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1answer
45 views

determining electrostatic field using only symmetries

As an exercise, I'm trying to (rigorously) determine as much as possible about the electrostatic field due to a infinite line of charge (along the z-axis) without using Maxwell's equations or any of ...
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31 views

Rearrangement of oil due to high voltage electric field

I've been working on a problem for some time now and I can't figure out why exactly this happens, and I've been looking for some insight. The phenomenon can be seen in this video. We can see that the ...
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1answer
144 views

Earnshaw Theorem for ionic solids

Is a single molecule of sodium chloride (say) or a cluster of molecules of NaCl unstable, although macroscopically NaCl is in fact, stable? How can I reason this based on Earnshaw's theorem?
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1answer
47 views

Charges on a tree

Can anyone tell me why is the tree in this photo charged with a positive charge although I thought it must be neutral.
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1answer
22 views

Electrostatic Shielding

suppose there is a solid conducting body with arbitrarily shaped cavity inside. Now a charge is placed inside the cavity.Now the entire setup is placed in an uniform electric field. Will the ...
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20 views

Can we lock electric charges in dielectric cells?

Suppose next. We using Wimshurst machine and gathering charges in dielectric cells such as mica .Before discharge we put whole machine in vacuum chamber.Question is next. Can we storage those charges ...
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31 views

The Equi-Potential Lines of Two Like Charges

Motivation Consider two Like charges $+q$ and $+q$ located on the $x$-axis with $x=-1$ and $x=+1$. Now, the potential inside the $xy$ plane will be $$V(x,y)=kq \left( ...
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59 views

What would be the capacitance of an unequal charged capacitor?

I searched for this question but I cannot get satisfactory answer. Say if we have a parallel plate or cylindrical capacitor and if I supply unequal charge to it how could I find its Capacitance. We ...
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Electric field in a sphere embedded in a medium

Consider a system where a sphere of conductivity $\sigma_i$ is embedded in a large medium of conductivity $\sigma_e$. An electric field $E_0$ is applied and the question is, what is the electric field ...
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55 views

Electric field due to charged disc, on the plane of the disc [closed]

A standard problem in finding the field is that of a uniformly charged disc, on its axis, but for this problem I'm supposed to find the potential and the field on the edge of the disc, i.e. in the ...
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1answer
39 views

How does electric potential relate to charge density in a wire?

Lets say we are talking about a wire with resistance connected to a battery. How is the charge density, taking into account bound and free charges, at two points connected to the electric potential ...
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56 views

What are the reasons for accepting Coulomb's law? [duplicate]

I read the Coulomb's first memoir on Electricity and Magnetism (Louis L. Bucciarelli english translated version), and found it to contain only three trials (as complained by many) to reach the ...
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2answers
57 views

where has the energy gone when the test charge turned away?

Consider an insulated ball with some charge $q_1$ inside it.Now we take a small area over that ball uninsulated i.e we had cut a small portion. Now when we bring a test charge from infinity near that ...
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1answer
49 views

Why is electric flux zero if my point charge is outside of a sphere? [duplicate]

I am currently studying Gauss Law and Electric flux , during one of my exercises they ask me to find the electric flux of a sphere with radius 5 cm and my point charge is 10 cm to the left of the ...
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2answers
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What are the advantages of multipole expansion of potentials?

When I see the equations of multipolar expansions they "look" to me harder than the original expressions. For example: Multipole expansion - spherical form, in Wikipedia I bet that this is not ...
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62 views

Electric field of a Uniformly charged sphere with a cavity [closed]

I have the following question: Consider a sphere of radius $R$, uniformly charged with a volume density $\rho$. The sphere has a spherical hole of radius $R/4$ at a distance $R/2$ from the ...
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29 views

Induced charges, electric potential

Consider a solid spherical conductor with charge Q on it, a charge q is placed at a distance r from the centre of sphere. Find the electric potential at the centre of sphere due to induced charges on ...
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14 views

Angular current in torus

I'm trying to find the magnetic field due to a torus anywhere in space. I'm approximating it as a circular current loop. What I'm having a hard time with is the current in the theta direction, that ...
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1answer
22 views

Electrostatic induction, induced charges

Is it true that If a conducting object is not grounded, the nearby charge will induce equal and opposite charges in the conducting object? It is mentioned in Wikipedia(electrostatic induction) but it ...
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3answers
44 views

How much energy does an electron have when it is situated right next to a negative point charge?

The formula for potential energy regarding point charges is $E=kQq/r$. If $r=0$, then will the energy be approaching infinity? But what about an electron in a parallel-plates situation where it is ...
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1answer
59 views

Laser-induced electrical discharge

Attracting lightning with an ion beam has been done in a lab but how strong of a laser is needed to reach the clouds to redirect the lightning bolt?
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29 views

How to find the polarization of a dielectric sphere with charged shell surrounding it?

A shell with negligible thickness has a given charge density as a function of theta, and is filled with a dielectric material with a given electric susceptibility. Using lovely legendre polynomials ...