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

2
votes
4answers
133 views

Why does $E=\nabla\phi$ follow from $\nabla\times E=0$?

I understand that using one of Maxwell's equations, $$\vec{\nabla} \times \vec{E}(\vec{x})=0,$$ it can be said that $$\vec{E}(\vec{x})=-\vec \nabla \phi(\vec{x}).$$ However, I can't find or ...
1
vote
2answers
62 views

Can a liquid insulator be electrically charged by touching a charged conductor?

Can a liquid insulator be electrically charged by touching a charged conductor? I understand that solid insulator will only be charge on the surface where it is touch, but the case is different ...
0
votes
0answers
28 views

Gauss law from Gauss divergence theorem [duplicate]

Apply Gauss divergence theorem to the gravitational field due to a spherical object of mass M and uniform density located at origin. Obtain Gauss law for gravitation in integral and differential ...
1
vote
1answer
128 views

Maxwells' equations and Coulomb's law

Coulomb's law and Maxwell's equations should be consistant as one can be derived from the other. Say we have a point charge with such a charge that $-kq=1$, meaning that at any point the electric ...
1
vote
1answer
24 views

What is the potential field of an ion near the Bohr radius?

I figure that at large enough distances, the potential field of an ion is just the Coulomb potential for its net charge. But what happens at scales comparable to the ion's Bohr radius? Could there be, ...
0
votes
2answers
76 views

A rod of charge?

Say you have a finite rod of conducting charge. The field from one side of the rod looks like Figure 1: At the centre of the sheet, the field lines are straight because of symmetry. (for an ...
0
votes
1answer
107 views

Questions about Van de Graaff generator

Only asking those questions because I can't afford to get a real generator. If the voltage on the sphere was 50 kV, then I used a metal rod to discharge it and I connected a voltmeter to wire ...
0
votes
1answer
49 views

Electric field from a sheet of charge?

Does anyone have images of the electric field created by a real plate of charge? I'm not looking for an image of a theoretical infinite sheet of charge, I'm looking for an image of a real large one. ...
0
votes
0answers
114 views

Field inside a conductor?

If the above image is a cross section of a conductor, the field at the point shown is not zero. So the field inside a conductor is not zero at all points. You could argue that the electrons would ...
0
votes
0answers
43 views

Different units in the equations of electrostatics in macroscopic media

I have the usual equations of electrostatics in macroscopic media expressed in Gaussian units: $$\nabla\cdot\vec{D}=4\pi\rho$$ $$\nabla\times\vec{E}=0$$ $$\vec{D}=\vec{E}+4\pi\vec{P} \tag1$$ My ...
0
votes
0answers
84 views

Force and Energy of interaction of conducting sphere and point charge

A completely isolated neutral conducting sphere of radius $R$ is kept such that its center is at a distance of $r\left(>R\right)$ from a point charge $+Q$. How can I find the force of ...
0
votes
0answers
25 views

Influence of a Capacitance Matrix of a voltage measurment

I am having a problem in understanding how in a multiconductor system the Capacitance Matrix influences the measure of voltage between two electrodes. In the case that interest me we have 4 ...
1
vote
3answers
147 views

Why is the field inside a hollow sphere zero?

Say you have a hollow sphere with a uniformly distributed charge on the surface. Why is the electric field everywhere inside the sphere zero? For the centre, its easy to add the vectors from the ...
0
votes
1answer
38 views

Capacitance of a free conductor

Consider a ideal conductor in free space.For all purposes here,the zero of the potential is taken at infinity. Suppose I give a charge $Q$ to the conductor.As a result,the conductor will have a ...
0
votes
3answers
247 views

Non-Conservative Behaviour of Static Electric Field

Static electric fields are supposed to be conservative in nature and therefore give $0J$ work if traversed over a loop. However in the following problem I got non zero work by a static electric field. ...
0
votes
0answers
25 views

Why is liquid behaving differently in electro osmosis and in electro spray?

Why is it that in electro osmosis the liquid will be attracted to the electrode having the same polarity sign as the one of the capillary walls but in electro spraying the liquid, once escaping the ...
3
votes
4answers
294 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 ...
1
vote
1answer
276 views

How to choose Gaussian surfaces while solving problems?

I have a doubt regarding this problem: Two large identical flat metal plates are placed parallel to one another, seperated by a small distance compared to their linear size. One plate is given a ...
7
votes
1answer
145 views

Understanding Calculus Notation in Physics

I have just started a first-year calculus-based physics course about electromagnetism and waves. I am having trouble understanding what calculus notation means in the context of physics. Here is a ...
0
votes
2answers
176 views

Does any object placed in an electric field change the electric field?

Lets say I have a point charge of magnitude $+q$, All around it I would have a symmetric radial electric field. Now if I place a neutral object lets say a sphere (doesn't matter insulating or ...
0
votes
0answers
45 views

Why is it easier to **just** rub charge onto something?

We have all experienced the mild zaps caused by static build up of charges due to triboelectric effect Electric field strenth of air = $ 3 × 10^6 Vm^{-1} $ Now, suppose we feel the zaps after ...
1
vote
1answer
92 views

Earnshaw's theorem and springs

Earnshaw's theorem states that the Laplacian of the potential energy of a small charge moving through a landscape full of static negative and/or positive charges (and gravity) is zero. Thus you can't ...
1
vote
1answer
77 views

Flux through a conduting cylinder?

A point charge of magnitude $Q$ is placed inside a conducting cylinder of length $L$ and radius $R$ at its centre. What is the flux through the cylinder? I know that I have to use Gauss Law here ...
1
vote
1answer
179 views

Surface charge density relation with the radius of curvature at the surface of a conductor [closed]

In a text book it was given that the surface charge density of a conductor at a particular region on its surface is inversely proportional to the radius of curvature at that region. I didn't ...
2
votes
1answer
185 views

Spherical harmonics

Given the following potential: $$V(\theta,\phi)=\frac{Q}{a}\left(\sin\theta \cos\phi+\frac{1}{2}\cos^2\theta\right)$$ on the surface of a sphere of radius $a$ I am trying to solve Laplace's Equation ...
0
votes
1answer
62 views

Capacitors in parallel and dieletric [closed]

I'm trying to solve this problem: Two capacitors of capacitance $C_1=200pF$ and $C_2=1000pF$ are connected in parallel and loaded to a potential difference of $400V$. Subsequently the space ...
0
votes
1answer
45 views

can we charge a neutral glass rod by touching it with charged glass rod?

Can we charge a neutral glass rod by touching it with charged glass rod?Can we charge similar objects by contact of which one is charged and other neutral?
0
votes
1answer
78 views

Show that the electric field, $\mathbf{\vec{E}}$ cannot be generated by any static distribution of charges

Show that the electric field $$\mathbf{\vec{E}}=\begin{pmatrix}0 \\ E_0x \\ 0\end{pmatrix}$$ where $E_0$ is a constant, cannot be generated by any static distribution of charges. I understand ...
0
votes
0answers
13 views

Is this configuration correct for this spherical capacitor? [duplicate]

This capacitance contain 4 dielectric as shown in the figure dielectric 1 in half sphere and 2,3 in for 1/4 of the sphere and the fourth one in the last 1/4 of the sphere as shown and I want to find ...
1
vote
2answers
317 views

Why are there dust particles on TV screens?

My professor gave us the following reason: The screen is positively charged. When dust particles fly near it, the positive charges in the screen induce a charge in the dust particle, pulling the ...
2
votes
1answer
75 views

what is the mechanism of water conductivity?

I'm trying to wrap my head around the kelvin water drop generator and more specifically what happens in the water before it drops. If on one side the drops of water are positive and on the other side ...
1
vote
1answer
54 views

Field created by a wire, known voltage

I am having some mental troubles with this problem I came across reading about transmission lines (I mean, it is not a problem from a book, I just thought about it). Say I have a couple of wires ...
1
vote
3answers
110 views

Why do I still get static shocks when hands are wet?

Quite a few times now I have washed my hands, and while my hands are still wet I will touch something metal and get a static shock. I thought static electricity doesn't really build up when there's a ...
1
vote
1answer
98 views

Why Gauss' law is applied?

Why Gauss' law is applied? Why is there a need of finding electric field by Gauss' law if we can find the electric field through Coulomb's law? or has it got more applications than Coulomb's law?
0
votes
2answers
101 views

Electric flux due to external charge

Why is electric flux due to external charge i.e a charge outside a closed surface equal to 0? P.S:Moreover I found this statement confusing:- Electric field appearing in the Gauss' law is the ...
0
votes
0answers
26 views

Proof of Gauss' Law [duplicate]

How would you prove Gauss' law for an asymmetrical closed surface? I can find it for symmetrical surface but couldn't for Asymmetrical surfaces.
1
vote
2answers
157 views

How is electric flux related to permittivity?

How is Gauss' law related to permittivity? I know that it equals $1/\epsilon_0$ times the magnitude of the charge enclosed. But, I'm unable to understand what it actually means. Can someone ...
-1
votes
1answer
67 views

What is opposite of electric field?

A negatively charged molecule will generate a field, an electric field, and it will repel all negative ions. So what does positively charged molecule generates that causes other positive molecules ...
0
votes
3answers
392 views

What happens when a charged (negative or positive) object touches an insulator?

I know that insulators do not conduct electricity because they do not allow the free movement of electrons. Let's assume the object that's going to touch the insulator is negatively charged. Does some ...
0
votes
0answers
29 views

Charges and their configurations

Can we treat any charge configuration as small point charges by using superimposition principle to derive electric fields, forces and other things ? For example suppose we have a symmetrically ...
2
votes
2answers
418 views

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?
1
vote
1answer
91 views

Can the electric field — always — be derived from the potential?

After studying the definition (& derivation) of the potential to an electric field and the Poisson equation I'm currently wondering whether the following is possible: Can one give an example of ...
1
vote
0answers
40 views

Do these steps demonstrate that acceleration of charged particle is proportional to current?

One formulation of Maxwell's Gauss Law for electric field is: $$\bigtriangledown E = 4 \pi k \rho $$ This can be worked into the Divergence Theorem as follows: $$\int\int_{A} F_\perp \:dA= 4\pi k ...
4
votes
2answers
115 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 ...
5
votes
1answer
110 views

Is there any good reason/argument/heuristic why one can approximate forces by approximating the potentials?

My question Is there any good reason/argument/heuristic why one can approximate forces by approximating the potentials? (As a concrete example, in Electrostatics.) Motivation for the question I am ...
3
votes
2answers
120 views

Relation between Gauss' law and Coulomb's law

In Coulomb's law if the relation was as if electric field intensity was to vary inversely $1/r$ with distance rather than the inverse $1/r^2$ of square of distance, would the Gauss's law still be ...
0
votes
1answer
86 views

Is there another way besides $V = k\int dq/r$ to find potential?

Suppose that the charge distribution $q(r)$ in the radial $r$-direction in a thin hollow disc of inner radius $a$ and outer radius $b$ is given by the power-law equation: $$q(r) = Q_0 \left[1 ...
1
vote
2answers
224 views

What do we mean exactly by the positive/negative charges in cathode and anode?

In batteries, what exactly do we mean by negative and positive charges? My understanding is that the negative charge of the anode is basically an atom with an extra electron in the last orbital and a ...
2
votes
1answer
61 views

Why does cloud-ground lightning occur so much less frequently over ocean?

I was talking with an acquaintance about lightning, and we came up with opposite theories and predictions for the frequency of lightning over ocean. My theory is that since seawater is a fluid ...
1
vote
1answer
349 views

The total energy of an electrostatic system

My problem is from Griffiths Introduction to Electrodynamics, Fourth Edition, p.112 Problem 2.60 (not homework): A point charge $q$ is at the center of an uncharged spherical conducting shell, ...