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.

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88 views

Can Gauss' Law in differential form apply to surface charges?

I'm calculating the electric field outside a coaxial cable using only Gauss' Law in differential form. The charge density on the interior solid conducting cylinder is exactly cancelled by the surface ...
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3answers
90 views

Electrostatic and gravitational forces? [closed]

Electrostatic force between two charged particles depends on the magnitude of the charges and the distance between them. If the charges have mass $m$ and $m'$ then, what will be the total force ...
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1answer
81 views

Issue with running a Van De Graaff generator

I am following this online video: http://www.youtube.com/watch?v=fsT69XnjxgU but my Van De Graaff generator is not working. I am using pvc pipes for the body, nylon and electrical tape as two rollers, ...
3
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2answers
497 views

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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1answer
63 views

Clarification of multipole expansion for a point charge

In Griffith's electrodynamic: 3.4.2 He pointed out that the monopole term is the exact potential for a single point charge. However I was under the impression that different configuration of a ...
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3answers
255 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 ...
2
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1answer
129 views

Electric field intensity of spherical shell (with cut out cap)

Consider a charged spherical shell of radius $R$ and surface charge density $\sigma$. Choose a point on the surface of the shell and cut a spherical cap of radius $a \ll R$. What is the electric field ...
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7answers
1k views

Why is there a factor of $4\pi$ in certain force equations?

I mean to ask why there is $4\pi$ present in force equations governing electricity? Though all objects in universe are not spherical and circular, the constant of proportionality in both equations ...
2
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1answer
69 views

What force keeps electrostatic charge from exiting a metals surface

I understand that in electrostatics all charges are 'static' due to equal forces acting upon them. This then leads to the fact that the arising electric field must be perpendicular to the metals ...
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6answers
2k views

Why cant Electrostatic field lines form closed loops?

My physics textbook says "Electrostatic field lines do not form closed loops. This is a consequence of the conservative nature of electric field." But I cant quite understand. Can anyone elaborate? ...
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1answer
65 views

Electric arc due to static discharge in a T-Shirt possible?

Yesterday, when I came home, I went to the bathroom (lights off) and i took off my T-Shirt (100% cotton) which I wore under a Shirt (50% cotton, 50% polyester). I believe to have seen a small but well ...
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0answers
26 views

An EM problem of polarized sphere

Today, I'm doing an EM problem and my question is exactly the same as this site shows: http://www.physicsforums.com/showthread.php?t=133501 To reiterate my confusion, why we can't use that integral ...
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3answers
141 views

question on dipole moment of water molecule

I read a line today and don't get it: "Molecules with mirror symmetry like oxygen, nitrogen, carbon dioxide, and carbon tetrachloride have no permanent dipole moments." ...
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4answers
382 views

Total Electrical potential energy of two particle system

I recently have been studying Electro-statics and I couldn't understand properly how the potential energy of two particle system is found. Suppose you have two particles with charges $Q_1$ and ...
2
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1answer
93 views

The position of center of mass of electron cloud in an atom

I read Griffiths EM today and it says something very interesting but a little bothering to me. It states for an atom, the position of center of mass of an electron cloud lies in the center of the ...
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0answers
53 views

What is conductivity?

I read that if we have spin $\frac{1}{2}$-particle, where a magetic force acts on, then the force is given by a drift speed times a conductivity. This conductivity is determined to be $\frac{kT}{D}$, ...
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1answer
37 views

Proton gas density

As far as I know the lightest gas is hydrogen due to low mass of its nucleus, but what if we were to somehow strip hydrogen atoms of electrons and enclose protons in a container made of teflon (high ...
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3answers
135 views

How can the potential on a cube's surface replicate the potential of a point particle?

If i have a cube (either hollow, or an insulating solid) and i want its surface have a potential such that it looks like a point particle outside of the box does that mean the exact potential on the ...
4
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2answers
137 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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1answer
63 views

Electric Potential Energy

When work is done on a positive test charge by an external force to move it from one location to another, does the potential energy increases or decreases, and does the electric potential increases or ...
2
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1answer
100 views

Slight variation to method of images

Suppose a point charge $q$ is located at $(x=0,y=0,z=d)$, and that along the $x$-$y$ plane is a infinite plate of potential $V = 0$. Then the method of images solves Laplace's equation for the ...
9
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1answer
678 views

Solve my confusion about electrons?

When a glass rod is rubbed with a silk cloth, both get charged: The silk gets positively charged and the rod gets negatively charged. My question is the following: How/why do these objects return to ...
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1answer
50 views

Gauss's law problem. ( Need someone to point me in the right direction) [closed]

What force per square meter pushes 2 infinite planes charged positively when their charge density is $0.3 \, \mu C/\mathrm{m}^2$ Second part is - using Gauss's theorem derive the equation ...
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1answer
59 views

Attraction and repulsion of charge? [duplicate]

Why do like charges on identical bodies cause a repulsion and unlike charges cause an attraction?
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3answers
5k views

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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1answer
116 views

Are the axial electric field lines of a dipole the only ones that extend to infinity?

Consider an electric dipole and its electric field lines. There will be many field lines that do not extend to or originate from infinity, but rather begin at the positive charge and loop back ...
3
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1answer
69 views

Correct formula to express the potential generated by a single layer charge distribution

Assume that the closed surface $S$ encircles a volume $V$, and that a surface charge with density $\sigma$ ("single layer") is distributed over $S$. My question regards the electrostatic potential ...
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2answers
123 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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4answers
234 views

Does an object's movement affect the likelihood of being struck by lightning?

Does the state of whether an object if moving or stationary affect the likelihood of it being struck by lightning? I suppose some things that could be considered would be: Whether the movement ...
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0answers
57 views

Debye Hückel Theory valid for ions?

I am wondering about the following: Is Debye Hückel Theory only used if you look at how an external "strong" field(like a potential by a sphere that has a charge that is 1000times higher than the ...
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1answer
264 views

Effect of electric field of plasma sheaths

How will an electric fields affect the formation of plasma sheaths?
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2answers
107 views

How does particles gain electrical charges and repel each others? (electrostatic stabilization)

When I study electrostatic stabilization, I understand that the particles have same charge and thus repel others, this is how colloid is stabilize. But how does particles gain electrical charges and ...
3
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1answer
83 views

Polarization vector and bound charge

Why is it that the bound charge is $Q_b = - \oint_S{\mathbf{P} \cdot d\mathbf{S}}$? In particular, why is there a negative sign? Hayt's book on electromagnetism describes this as the "net increase in ...
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3answers
596 views

when we rub objects together, what determines which material will pick up electrons?

For example We know glass when rubbed by silk will become positively charged while the silk will be charged negative. What exactly makes glass appropriate for losing electrons in that experiment? (
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1answer
51 views

In what ratio does the charge distribute if a charge and uncharged body touch each other?

Lets say a large charged body has $n$ elementary charges and is brought in contact with a small uncharged body. When the charge distributes, does it distribute in the ratio of number of atoms or each ...
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3answers
5k views

Why is electric field strong at sharp edges?

I learned about the coronal discharge, and the common explanation is because the electric field is strong where radius of curvature is small. But I haven't found anything yet that explains why ...
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2answers
1k views

Why potential energy of a dipole in an electric field has a negative sign?

In the following equation $$V = -\mathbf{P}\cdot \mathbf{E}$$ why I have to take Potential Energy as negative. Is there any simple reason behind this ? I am preparing for my high school ...
2
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2answers
120 views

Absolute value in the argument of a logarithm

I am wondering how the author rationalizes the removal of absolute value bars around the quotient argument of a natural logarithm. My take on this is that the potential at point $b$ MUST be greater ...
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4answers
4k views

What is the electric potential at a point?

1) What does the electric potential at a point exactly mean? My teacher tells me that current flows from higher potential to lower potential but when I ask him the reason, he fails to give me a ...
2
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0answers
38 views

electrons in elecrtostatic force(please read specification given below) [duplicate]

when comb is rubbed with hair, and brought near small pieces of papers, small paper pieces gets a towards comb. Here the comb gets negatively charged and when brought near piece of paper where do ...
0
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1answer
39 views

Current and Voltage of electrostatic discharge

I conducted an experiment , i put a silver foil on a a CRT TV , then i open the TV, charging the foil (acting like a capacitor plate), if i approach a grounded rod to it , it will discharge with a ...
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1answer
30 views

Charging one thing with static electricity by using battery

How can I make one thing to get statically charged by using batteries but not friction ? For example charge a rod so it can attract shredding ?
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0answers
53 views

Resistance of a cylinder contacted by two smaller circular faces

Suppose we have a solid homogeneous cylinder with radius $a$, heigth $h$ and conductivity $\sigma$. The top and the bottom face is contacted with a smaller circular face with radius $b$. How can I ...
2
votes
1answer
66 views

Capacitor in series?

Say you have two charged capacitors in series. Zoom in on one capacitor. For this specific capacitor, the charge on the two plates will be the same in magnitude, according to my textbook. My teacher ...
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1answer
91 views

Field from non-conducting plate?

For a non-conducting sheet, the electric field is given by: $$E = \frac{\sigma}{2\epsilon_0}$$ where $\sigma$ is the surface charge density. This equation holds well for a finite ...
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2answers
3k views

If we change the radius of spherical surface does electric field or flux change?

Suppose a point charge is located at the center of a spherical surface. The electric field at the surface of the sphere and the total flux through the sphere are determined. 1).What happens ...
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2answers
165 views

Charge distribution on conductors?

You have seen that the excess charge on an isolated conductor moves entirely to the conductor’s surface. However, unless the conductor is spherical, the charge does not distribute itself uniformly. ...
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4answers
337 views

Is a capacitor in an open circuit charged?

Say I have a circuit consisting of a battery, a wire, an open switch, and a capacitor. The circuit is open since the switch is open. My book says that the capacitor will only be charged when the ...
0
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1answer
202 views

How do you solve Laplace's equation for a parallel plate capacitor?

I would like to find the analytic solution to the problem of two plates of opposite electric potential. I have already solved this numerically as shown in the picture below. I'm also wondering what ...
2
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1answer
139 views

Why the electric potential of earth is zero?

For a localized charge distribution the potential is set to zero far away from the charge distribution (at infinity) Now, when grounding a conductor, i.e. connecting it to Earth, it is said that we ...