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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What is charge actually? How to define it? [closed]

Is charge of something for (e.g.) an electron related to electromagnetic space if it exists due to energy, due to which it may have mass? I don't know about quantum mechanics or advanced particle ...
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970 views

Why is the electric field of an infinite insulated plane of charge perpendicular to the plane?

I'm studying Gauss' Law, and I came across a section where we're supposed to find the electric field of various shapes (like an infinite line of charges, etc), and for an infinite plane with a uniform ...
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986 views

Divergence of a field and its interpretation

The divergence of an electric field due to a point charge (according to Coulomb's law) is zero. In literature the divergence of a field indicates presence/absence of a sink/source for the field. ...
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908 views

Why is surface charge distribution uniform for a conducting sphere? Can't it be arbitrary?

If the charge $q_1$ has to repel the charge $q_2$, the electric field has to go inside the conductor which contradicts the fact that electric field inside conductors is zero. Then why do the charges ...
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How does electricity flow in conductor when potential difference is applied?

Electrons move from higher potential to lower potential. When a conductor is connected to battery, electron move from negative terminal to positive terminal. But the battery itself forms a Electric ...
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Capacitor with different charges on each plate

I am confused as to whether/how capacitance changes when each plate has a different charge. For example, consider a coaxial cable and put $20Q$ on the outer cable, and $-Q$ on the inner. Or how about ...
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461 views

Gauss' law and an external charge

Gauss' law states that the net outward normal electric flux through a closed surface is equal to $q_{total, inside}/\epsilon_0$. However, I'm a bit confused of why the presence of an external charge ...
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490 views

Change in attraction of charged bodies

If I insert a piece of glass between two objects carrying different charges, would they still attract? If they attract, does the piece of glass affect the force of attraction and is there any formula ...
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813 views

Sign of Work and potential energy in electrostatics

Conceptual question: Suppose we have a configuration of point charges. If the potential of the energy of the system is negative, this means work is positive. I'm kind of rusty with my mechanics, ...
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If we charge a capacitor can we discharge it into a battery?

I have read that we can charge a capacitor using a battery, but can the vice versa happen? My project needs to show a battery being charged through a fully charged capacitor.
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366 views

2D Gauss law vs residue theorem

I used to have a vague feeling that the residue theorem is a close analogy to 2D electrostatics in which the residues themselves play a role of point charges. However, the equations don't seem to add ...
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Using the image charges method to find the electric field

The following is a question from a tutorial in my Physics 2 course about conductors and the Method of image charges. We are given two infinite perpendicular and grounded plains. The first ...
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371 views

Do inner shell electrons feel the electric field/force from an outer shell electron in an atom?

We just finished studying Gauss’ law and were puzzled by this thought. If I look at a copper atom and focus on the 29th electron in the 4th shell, according to Gauss’ law, I can draw a Gaussian ...
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862 views

Meaning of the phrase “dipole moment of the combination”

Here is a question I came across in a book: Three point charges $-q$,$-q$ and $2q$ are placed on the vertices of an equilateral triangle of side length $d$ units.What is the dipole moment of the ...
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Infinitely charged wire and Differential form of Gauss' Law

I have tried calculating the potential of a charged wire the direct way. If lambda is the charge density of the wire, then I get $$\phi(r) = \frac{\lambda}{4 \pi \epsilon_0 r} \int_{-\infty}^\infty ...
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Why can you make two repelling positively charged rods touch? Shouldn't the Coulomb force become infinite?

For a physics lab on the Triboelectric effect, we rubbed two rods with fur which gave both of them a positive charge. We then brought them close together, and they obviously repelled. We then held ...
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Is the Earth negatively or positively charged?

The Earth carries a negative electric charge of roughly 500 thousand Coulombs. Does that mean the Earth is negatively charged?
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What are electromagnetic fields made of?

I am trying to understand electromagnetic fields so I have two question related to them. What is a electromagnetic field made of? Is it made of photons / virtual photons? How about a static electric ...
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Why we cannot use Gauss's Law to find the Electric Field of a finite-length charged wire?

One of my physics books has a nice example on how to use Gauss's Law to find the electric field of a long (infinite) charged wire. However, at the very end of the example, the author ends by saying ...
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520 views

Sparks from van de graff generator

I was at a lecture yesterday and there was a demo of a van de graff generator. He held the smaller metal globe which is attached by a wire, about 4cm from the main globe. This created a spark between ...
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306 views

Couch shocks everything!

How do I get rid of the static charge I get from my microfiber couches? Every time I get up and touch something it zaps me... I'm mostly worried about my laptop getting fried.
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What restores balance to a repulsive electric force on an electroscope?

I am an amateur physics enthusiast (during the day I am a police officer), and recently, I learned how to build an electroscope. I regret that I am learning how wonderful our universe is so late in my ...
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1answer
138 views

Integrating Radial Vector Fields

Given a integral $$\int_vd^3{r} \;\vec{r}\;\rho(r)$$ and How do you convert it to spherical coordinate system, noting that $\rho(r)$ is indeed as it is without vector, i.e. it is spherically symmetric ...
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Will there be any force of attraction or repulsion between an electrified body and a non-electrified body?

Up to my knowledge an electrified (charged) body can attract a non-electrified (neutral) body. I thought this because, when we bring a charged (suppose negatively charged) body near a neutral one. ...
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1answer
178 views

Experimental relationship between linear dependence and superposition

From Griffith's Introduction to Electrodynamics The principle of superposition may seem obvious to you, but it did not have to be so simple: if the electromagnetic force were proportional to the ...
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1k views

Speakers and Static from Hands

Why is it that when you touch the a bare male end of a speaker feed that the speaker makes hissing noises? Is it just (eddy?) currents running through you?
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Why the direction of dipole moment is from negative charge to positive charge?

An electric dipole moment is defined as $p = q\times 2d$. How to understand it physically? Why the direction of the electric dipole moment is from negative charge to positive charge?
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The formula of the force exerted on an electric dipole by non-uniform electric field

When an electric dipole of moment $\mathbf{P}$ is located in a non-uniform electric field $\mathbf{E}$, there is an net force exerted on it. However, the formula of the force in some books is read ...
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Electrostatic Pressure Concept

There was a Question bothering me. I tried solving it But couldn't So I finally went up to my teacher asked him for help . He told me that there was a formula for Electrostatic pressure ...
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4answers
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In electrostatics, why the conductor is an equipotential surface?

Since the electric field inside a conductor is zero that means the potential is constant inside a conductor, which means the "inside" of a conductor is an equipotential region. Why books conclude ...
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1answer
458 views

Balloon rubbing; where do the electrons go?

If you rubbed a balloon with a towel, where would the electrons go: the balloon or the towel? Why? I'm guessing the electrons would go to the object with a larger mass, but it's just a guess. :)
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142 views

Conductors and Uniqueness Theorem

I'm working with Griffiths Electrodynamics, and he introduces a uniqueness theorem: First Uniqueness Theorem: The potential $V$ in a volume $\Omega$ is uniquely determined if (a) the charge ...
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3answers
828 views

Field due to current in a wire

Suppose a current flows in a straight cylindrical wire so that an electric field $\textbf{E}$ is maintained in the wire. Will there be an electric field just outside the wire..?
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How is Gauss' Law (integral form) arrived at from Coulomb's Law, and how is the differential form arrived at from that?

On a similar note: when using Gauss' Law, do you even begin with Coulomb's law, or does one take it as given that flux is the surface integral of the Electric field in the direction of the normal to ...
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521 views

Algorithm of Lightning Strikes? [duplicate]

Given an array of charge for a given area (2D or 3D), what algorithm would describe the path that lightning takes? An example algorithm would be from the highest charge of the cloud, find the lowest ...
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1answer
166 views

Simulate / plot electrostatic field

I have something like this: For given voltage (9 V red wire, 0 V blue wire) I want to simulate electrostatic field. I already know, for example that in the point (10.5;0) there are 10 V and etc. I ...
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1answer
325 views

Coulomb interaction as virtual particles exchange?

I've been reading about virtual particle exchanges in physics books and in Physics SA posts, where a particle interpretation of gravity and Coulomb interaction is established. The Feynman Diagram ...
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1answer
341 views

Information content of the electrostatic Maxwell equations vs Coulomb's Law vs Poisson's Equation

In electrostatics, we have Maxwell's equations: $\nabla \cdot E = \rho$ $\nabla \times E = 0$ These four equations (the second line standing for three equations) can also be written in terms of the ...
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1answer
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What are the limits of applicability of Coulomb's Law?

Coulomb's law is formally parallel to Newton's Law of Universal Gravitation, which is known to give way to General Relativity for very large masses. Does Coulomb's Law have any similar limits of ...
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500 views

Conservation of Charge and Method of Images

Consider the typical problem, "You have a conducting sphere of charge $Q$ and a point charge q a certain distance away, what is the force on the point charge?". The solution is a simple application of ...
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2answers
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How does rubbing cause the transfer of electrons from one object to the other? [duplicate]

I have just learnt about electrostatics. Why would there be a transfer of electrons? Is it because of the difference of the materials (i.e. triboelectric series)? So in the case of two different ...
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3answers
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“Find the net force the southern hemisphere of a uniformly charged sphere exerts on the northern hemisphere”

This is Griffiths, Introduction to Electrodynamics, 2.43, if you have the book. The problem states Find the net force that the southern hemisphere of a uniformly charged sphere exerts on the ...
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How to get the electric field strength of a plate as approximation of a sphere

Suppose you know that the electric field in distance $r > R$ from the center of a charged sphere with charge $Q$ and radius $R$ is given by: $$ E = \frac{1}{4\pi\epsilon_0} \frac{Q}{r^2} $$ ...
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1answer
117 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 ...
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1answer
398 views

Calculating the electrostatic energy per unit length of a cylindrical shell surrounded by a coaxial cable

Suppose an infinitely long cylindrical shell of radius $a$ carries a surface charge density $\sigma_0$ and is surrounded by a coaxial cable of inner radius $b$ and outer radius $c$ with uniform charge ...
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2answers
426 views

Electric field in a sphere with a cylindrical hole drilled through it

Suppose that you have a sphere of radius $R$ and uniform charge density $\rho$; a cylindrical hole with radius $a$ ($a\ll R$) is drilled through the center of the sphere, leaving it like a "necklace ...
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2answers
153 views

Argument for symmetry of potential

Consider the following electrostatic charge configuration of a spherically symmetric, perfect conductor with total charge $Q = 2q$, where $q > 0$. A point charge $q$ is placed at the position ...
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762 views

Conductors and their charge?

Why does excess positive charge stay on the surface of a conductor? This is what I understood from: How does positive charge spread out in conductors? and other resources on the web: If there is a ...
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2answers
159 views

In Jackson's expression for the electrostatic Green function, why is the Laplacian taken with respect to the primed coordinates?

Jackson writes, The function $1/|\mathbf{x} - \mathbf{x}'|$ is only one of a class of functions depending on the variables $\mathbf{x}$ and $\mathbf{x}'$, and called Green functions, which satisfy ...
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195 views

What happens to this potential energy?

Let's say I turn on a Van de Graaff which creates a large positive charge. Now let's say I have an object with a positive charge in my hand and I start walking toward the Van de Graaff from $x$ meters ...