Electrostatics is concerned with the field and potential of stationary electrical charges and electric charge distributions. Problems are this type are almost exclusively concerned with mathematics of geometries using the inverse-square law.

learn more… | top users | synonyms

0
votes
1answer
506 views

Linear charge density, surface charge density and volume charge density

What is the difference among: linear charge density, surface charge density, and volume charge density?
1
vote
2answers
114 views

Can protons in the nucleus of an atom be aligned by electromagnetic fields?

Can protons in the nucleus of an atom be aligned by electromagnetic fields? If so can it be done around $-135°C$ zero?
0
votes
3answers
2k views

Why does the area of the plates affect the capacitance?

Why does the area of the plates affect the capacitance? Lets say I have a parallel plate capacitor with a charge of 10C and a potential difference of 5V. By the definition $C=Q/V$, the capacitance is ...
1
vote
1answer
55 views

Uniqueness of equilibria in electrostatics

I have the following problem. Suppose we place some continuous charge distribution (with total charge $Q$)on some conducting domain. The charge will redistribute itself on the domain until it's in ...
1
vote
3answers
194 views

Homework question about electric field between two spheres

I was helping a friend of mine with the following question from Knight's book and I was not able to answer part (c). Here is what I think I know: (a) I expect $V_1 = V_2$; the two spheres are in ...
5
votes
1answer
195 views

Density of repulsive particles on a disk?

NB: the external circle (where particle or water is in it) is fixed ! It's a 2D theoretical problem (just for understand something in particular). Here, no gravity, no temperature. I put in a disk a ...
1
vote
3answers
587 views

2 dimensional Coulomb's law equation

We can notice that in the Coulomb's law equation, $$\begin{equation}\tag{1}F=\frac{1}{4\pi\epsilon}\cdot\frac{q_1q_2}{r^2}\end{equation} $$ $4\pi r^2$ factor in the denominator expresses directly ...
1
vote
2answers
76 views

Charged spheres - help with method to work these out? [closed]

Can anyone demonstrate how to get the answers to these questions? I'm just interested in the method I need to use in order to obtain the correct answer no matter what the values are. Three small ...
1
vote
1answer
78 views

Analytic solution of particle in electric field [closed]

This is homework and I need some guidance. The question I struggle with is: Place a particle with $m=2$ , $q=3$ in a constant electric field $\vec{E}=(5,0,0)$ Choose $\vec{r}(0)=(0,0,0)$ and ...
2
votes
1answer
93 views

If Electricity and magnetism are the same viewed from a different reference frame then is electricity medium dependant?

If Electricity and magnetism are the same viewed from a different reference frame (they are the same force as unified by maxwell) then is electricity medium dependant? I came to this question when ...
7
votes
3answers
359 views

electric field inside a conductor?

We have studied so far that electric field inside a conductor if no charge is placed inside is zero. But we know that every conductor has only a limited number of electrons. What happens when ALL the ...
2
votes
1answer
285 views

Electrostatics:2 concentric spheres

An external charge when brought close to a conductor induces bound charges on the nearer side and free charges on the further side so that the field induced in the conductor can counterbalance the ...
1
vote
1answer
254 views

Why the electric bulb turns on almost instantly when the switch is closed? [duplicate]

The electron drift speed is estimated to be very low.How could there is current almost the instant a circuit is closed?? By the discussions it is known that The information about beginning of the ...
5
votes
2answers
442 views

How does one show using QED that same/opposite electric charges repel/attract each other, respectively?

Why do same charges repel each other and opposite charges attract each other (please explain the phenomenon using real laws of nature (QED) not with the approximation model)?
2
votes
0answers
224 views

Calculating Electric Field from a Potential Difference w/o Charge

So here is my homework question: Two long cylindrical shells of metal (radii $r_1$ and $r_2$, $r_2 > r_1$) are arranged coaxially. The plates are maintained at the potential difference ...
3
votes
2answers
92 views

Why is charge $q$ symmetrically distributed?

Simple question: Why is charge $q$ outside symmetrically distributed? The material is a conductor.
3
votes
2answers
161 views

Why 3 dipole terms in a multipole expansion?

As can be seen on this page http://en.wikipedia.org/wiki/Multipole_expansion when we take a multipole expansion without assuming azimuthal symmetry we end up with $2l+1$ coefficients for the $l^{th}$ ...
0
votes
0answers
56 views

why boundary condition in steady electric current?

when we electric field between two conductors in certain direction the current density should pass in its direction why current density direction change at boundary although the direction of electric ...
0
votes
1answer
1k views

Electric field due to nonconducting sphere

For calculating electric field outside a nonconducting sphere with a hollow spherical cavity. When I use the rule (Charge density= $dQ/dV$), I don't know exactly what is $dV$, is the volume here ...
2
votes
3answers
469 views

Potential Inside Conducting Cube

A cubical box with sides of length L consists of six metal plates. Five sides of the box { the plates at $x=0, x=L, y=0, y=L, z=0$ - are grounded. The top of the box (at z = L) is made of a separate ...
0
votes
0answers
97 views

Variation of electric field and current flowing

Theoretically, a change in either electric or magnetic field will cause a current to flow , I am already familiar to Faraday's law of electromagnetic induction, so I tried to search about producing a ...
2
votes
2answers
173 views

My conundrum with Gauss’ law in electrostatics

If I use Gauss’ law to calculate the electric field outside of a charged (conducting or insulating) sphere or a point charge, the fields are the same. However, as a test approaches a point charge, the ...
-2
votes
1answer
633 views

Net flux calculation through a cube [closed]

Ans: Applying Gauss’s law the net flux can be calculated. And for option (B), I guess the flux will be 0. But not sure. Can anyone explain all the 3 options? For left and rignt face, EA = ...
2
votes
1answer
183 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 ...
3
votes
3answers
2k views

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 ...
1
vote
1answer
193 views

EM force, blocking force carrier photons in a static electric field

I am doing some personal research in this specific area and wanted to ask something related to photons and EM force. are involved. Here is a thought experiment that doesn't add up to observed results, ...
0
votes
2answers
240 views

Is Ohm's law obeyed in power transmission?

We learnt in high school that according to OHM'S law V/I=R.. i.e.V proportional to I.. We also learnt that during power transmission in an electric line P=VI and that inorder to minimise loss voltage ...
3
votes
1answer
202 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 ...
1
vote
2answers
68 views

Capacitor's voltage

Imagine I have two plates that form a capacitor, so the magnitude of the charge in each plate is, let's say, $Q$. So, the force, in respect to the distance $d$, is gonna be: $$F(d) = ...
2
votes
2answers
3k views

Electric Field Between Two Parallel Infinite Plates of Positive Charge and a Gaussian Cylinder

Is the electric field between two positively charged parallel infinite plates one with a charge density twice the other effect the electric field on the outside of the plates? I am thinking no, ...
1
vote
1answer
152 views

Coulomb force on the center of a hexagon?

Six point charges $q$ are at the corners of a regular hexagon that has sides of length $a$. What is the force on another charge $Q$ which is located in the center of the hexagon? What is the force on ...
1
vote
1answer
194 views

How to find Electrostatic Potential Difference?

I have a really simple doubt about finding the potential difference in electrostatics. Well, first of all, the definition of potential difference is very clear to me: we take a path between the points ...
7
votes
4answers
306 views

Distribution of point charges on a line of finite length

How will $N$ freely moving charges confined to a line with length $L$ be distributed? What are their equilibrium positions?
3
votes
2answers
277 views

Shape of electric charges on sphere in equilibrium state

When electric charges of equal magnitude and sign are released on a regular sphere (and assume that they stick to the surface of the sphere, but they are free to move along its surface), what is the ...
3
votes
2answers
357 views

Prove a dielectric with infinite dielectric constant behaves as a conductor for static fields

I read the following problem: Prove that a dielectric medium for which $\varepsilon \to \infty$ behaves as a perfect conductor in the presence of static electric fields. So, the easy part is that the ...
0
votes
1answer
122 views

what is in the electrostatic field that makes the word done independent of path taken?

I am trying to understand how is it possible for electric force to behave like this (path independence)? I am repeatedly failing to get an intuitive meaning behind its (electric field) nature of ...
1
vote
1answer
81 views

Where do electrical charges go, on a nonconductor dielectric when we make it charged?

My question is about electrically nonconductor dielectrics. We know such materials don't possess free charges.They have atoms bound together and every atom has specific numbers of electrons turning ...
2
votes
1answer
94 views

Behavior of the electric field on boundary surfaces

Consider this picture. Integrating over this infinitesimal box gives the following equivalencies: $$\int_{\Delta V} d^3r~{\rm div} \vec{E}(\vec{r}) = \int_{S(\Delta V)} d\vec{f} \cdot ...
1
vote
1answer
57 views

Need a more efficient way to find where the $E$ field is zero

So this is a problem I already know how to solve, but I feel like my method is really inefficient and I'm wondering if there's a more intuitive, less tedious way to arrive at this conclusion. If we ...
9
votes
2answers
1k views

Tension in a curved charged wire (electrostatic force) - does wire thickness matter?

Consider a conducting wire bent in a circle (alternatively, a perfectly smooth metal ring) with a positive (or negative) electric charge on it. Technically, this shape constitutes a torus. Assume ...
2
votes
3answers
274 views

Electrostatic energy integral for point charges

The electric energy stored in a system of two point charges $Q_1$ and $Q_2$ is simply $$W = \frac{1}{4\pi\epsilon_0}\frac{Q_1Q_2}{a}$$ where $a$ is the distance between them. However, the total ...
1
vote
0answers
76 views

Understanding unit vectors

Trying to understand how the unit vector ${\mathcal{\hat{r}}}$ defined as $\frac{r' - r}{|r' - r|} $ (where $r'$ is the source point) works in this problem: Work out the electric field, $E$, at point ...
4
votes
1answer
406 views

Electrostatic adhesion instead of glue. Is it possible?

I am thinking about the way to attach the printed photographs to the wall but not using the frame. And the most interesting idea for me is the use of electrostatics. In addition I have found the ...
4
votes
1answer
108 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 ...
-1
votes
1answer
232 views

Electric field of an infinitely long (thin) metal cylinder [closed]

An infinitely long thin metal cylinder of radius $a$ coaxial with the $z$ axis carries a uniform surface charge density $\sigma=\frac{\lambda}{2\pi a}$, where $\lambda$ is a constant. A thick ...
3
votes
2answers
151 views

Moving the plates of a charged capacitor to calculate energy density - where's the flaw in my argument?

For a charged air-dielectric capacitor, let the plates be parallel to the $xy$ plane, with the top carrying a positive charge $+Q$, the bottom a charge $-Q$. The force on an infinitesimal charge ...
1
vote
1answer
474 views

Finding Electric Field outside a Charged Cylinder

I'm trying to solve a problem that involves finding the electric field due to a uniformly cylinder of radius $r$, length $L$ and total charge $Q$. Well, my thought was: if I am to use Gauss' Law, I'll ...
3
votes
1answer
280 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 ...
2
votes
0answers
90 views

mathematical model of one electrostatic problem

I am trying to find direct-current electric field in a specific domain: it is a brick made from a low-conductive material with a number of more conductive inclusions of different shapes - spheres, ...
2
votes
0answers
100 views

Where can I find a database for dielectric constants in the visible range?

I am looking for a database of dielectric constants in the visible range and I could not find them by Googling, so I was wondering whether anybody here knows where I can find those parameters for some ...