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 [tag:magnetic-...

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2
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2answers
3k views

The electric field of a conductive sphere containing a charge - grounded vs not grounded

Let's suppose we have a sphere but unlike theoretical ones it'll have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge $q$ ...
2
votes
1answer
519 views

Image method to calculate the surface charge density on a conducting plate

There is a charge $q$ at a perpendicular distance $z = d$ from an infinite conducting plate $z=0$. We use the image method and place $-q$ on the other side of the plate and calculate the field. This ...
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1answer
27 views

Electrostatics of hollow conductors

My textbook says: Inside a conductor, electric field is zero. The interior of a conductor can have no excess charge in static situation. Electric field just outside a charged conductor is ...
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2answers
45 views

Formula for discontinuity of electric field across boundary

The formula for the discontinuity of the electric field across a boundary is given by$$\vec{E}_{\text{above}} - \vec{E}_{\text{below}} = \frac{\sigma}{\epsilon_0} \hat{n}.$$ In the derivation of this ...
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1answer
33 views

Reduced electric field strength in dielectric

Under what conditions does the field due to free charge is simply reduced by factor of 1/k where k is dielectric constant? I.e my book says if dielectric is entirely ...
1
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2answers
153 views

Help understanding the solution to a problem regarding kinetic energy of a group of point charges

The problem provided by my professor goes as follows: "Now consider a situation in which all charges are equal to q and they simultaneously become "unglued". What speed will each charge have when a ...
-2
votes
1answer
58 views

Why $\epsilon_0 = 1/(4\pi k)$ instead of $\epsilon_0 = 4\pi k$? [on hold]

In my physics book, they consider a positive point charge $q$ and a spherical surface of radius $r$ centered on this positive charge. Then the flux through this surface is given by $$\Phi = \iint \vec{...
5
votes
1answer
618 views

Finding Green function using eigenfunction expansion method

Given the Dirichlet boundary condition, I am to show that the functions that satisfy $$(\nabla ^2 + k_{lmn}^2) \psi_{lmn} (x,y,z) = 0$$ are given by $$\psi_{lmn} = (\frac{\pi}{2x})^{1/2} J_{l+...
1
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2answers
775 views

How does the magnetic field get induced in car's tire?

I was amazed to see how my car's tire started attracting the nuts and bolts, how in the world did it induce the magnetic field? Never heard of such phenomena!!!
0
votes
4answers
211 views

Can the potential difference produced in Van De Graff generator used to generate electric current?

If this machine can build up high voltages of the order of millions of volts, can we use this voltage to generate a current of electrons? The building up of potential difference can result in an ...
1
vote
2answers
106 views

How can plants rooted on the ground become charged?

According to a quote on the physics forum "Plants are usually charged negatively and emit weak electric fields." Reference However this seems to contradict the fact that plants are grounded and any ...
8
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1answer
221 views

Physical interpretation related to a non-linear partial differential equation

I am doctoral student in pure mathematics working on a particular problem. My question is if this problem has applications to real world phenomena. I will try to explain the direct problem starting ...
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0answers
34 views

How to understand method of images in electrostatics without much maths

How do you explain Method of images for school students without much maths i.e without boundary condition or uniqueness theorem. If it's not possible what are the rules to be followed to solve ...
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1answer
14 views
6
votes
1answer
181 views

Potential function - numerical simulation

Using MATLAB, I fixed the potential in a region inside a rectangular plate (100 V) and in the border (50 V). I got the following result of the potential along the plate: I can't find an intuitive ...
12
votes
6answers
3k views

Why does the density of electric field lines make sense, if there is a field line through every point?

When we're dealing with problems in electrostatics (especially when we use Gauss' law) we often refer to the density of electric field lines, which is inversely proportional to the radius in the case ...
0
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0answers
20 views

Electric field inside hollow metallic sphere which is not closed

Suppose I have a charged hollow metallic sphere. It is sure that the electric field inside the sphere is zero, in static case. ( I got explanation for this from the previous discussions in this site). ...
-2
votes
0answers
36 views

What is Coulumb force at zero separation in classical picture [closed]

Assume a classical world. What would be force between 2 point charges if their separation tends to zero? Assume charges are static. My professor claimed it would be finite. I request you to ...
4
votes
1answer
542 views

Determining potential in coaxial cylinders

If I have two conducting, coaxial cylinders as shown: The potential at the outer cylinder is = 0. And I apply a potential difference across both cylinders in the form $V_a - V_b = V_{ab}$, how can ...
2
votes
0answers
56 views

Gauss' Law and Electric Field Close to a Ball

So I've learned about Gauss' law and I have something in my head. Why does electric field that is very close to a ball is not close to infinity. Take a look at this image: As we can see, if we make ...
-2
votes
0answers
25 views

Electric Field around Uniformly Charged Rod [closed]

Question: A uniformly charged rod (length = $2.0~m$, charge per unit length = $3.0~nC/m$) lies on the x-axis. In consultation with your lecture notes, calculate the magnitude of the electric field at ...
2
votes
2answers
26 views

Charge distribution on a conductor surface

I understand that if a conductor was charged with a charge of say 1 coulomb, the charge would spread uniformly over it's entire surface to neutralize any difference in potential. However, and though ...
1
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1answer
38 views

Effect of test charge on electric field intensity

Obviously on the macroscopic scale, having a test charge being a proton produces no noticeable change in the electric field produced by a charged body. However, on the microscopic level this would ...
6
votes
0answers
395 views

Modified Coulomb potential [closed]

I'm working through Byron and Fuller's "Mathematics of Classical and Quantum Physics" and came across this problem: If the electric potential of a point charge were $\phi(r) = \frac{q}{r^{1-\...
3
votes
1answer
55 views

Removing an electron from a conductor

I'm trying to understand how to think of and visualize a conductor where charge is added. As I understand, conductor are defined as materials (where the nucleus is stationary) that permit electrons ...
1
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3answers
67 views

Intuitive explanation for uniform electric field between capacitor plates

Could anyone explain why the intensity of the electric field between plates of a charged capacitor is constant? Moreover, the varying the distance between plates doesn't change the electric field ...
4
votes
1answer
170 views

Problem from Purcell and Morin's Electricity and Magnetism: Holding the charge in place

This is the problem given in Purcell and Morin's electricity and magnetism book. (Problem 3.2 If you have the book) Figure: I was able to figure out that the charges on A,B,C,D cant be held ...
6
votes
2answers
57 views

Significance of electrical fields of infinite objects

I've noticed a pattern with the electric fields of charged objects of infinite dimensions. A point charge, which can be considered a charge of 0 dimensions, has an electric field that goes as $r^{-2}$...
3
votes
2answers
178 views

Question regarding Van De Graff generator Belt

I have made a VDG generator with a rubber band as the belt and a glass roller. It doesnt seem to work because I think the rubber band may be conductive. I was thinking of using other materials for ...
1
vote
0answers
31 views

Discontinuity of electric field formula [closed]

I'm trying to understand where the formula for the discontinuity of an electric field when you cross a uniformly charged surface comes from: $$\vec{E}_{\textrm{above}} - \vec{E}_{\textrm{below}} = \...
0
votes
1answer
75 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 make 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 ...
0
votes
1answer
105 views

How do I get the angle for the $x$ and $y$ component of the electric field for four equidistant particles?

Four particles form a square of edge length $a= 5.00\ cm$ and have charges $q_1= +10\ nC$, $q_2=-20\ nC$, $q_3=20\ nC$, and $q_4=-10\ nC$. In unit vector notation, what is the net electric field the ...
0
votes
1answer
15 views

System of point charges, work to move one of the systems point charge around

Suppose we have an electron at $\vec{x}_1=(0,a,0)$ and a proton at $\vec{x}_(a,0,0)$. Now i want to move the proton to the point $\vec{x}_3 = (0,0,0)$ and want to know how much work do i need for that....
1
vote
1answer
23 views

System of point charges, Potential related question

Suppose we have two point charges in the Cartesian coordinate system. $q_1= e, q_2 = 2e$, where $q_1$ is positioned at $(0,0,0)$ and $q_2$ at $(a,0,0)$ for $a > 0 $. Further there is a point charge ...
0
votes
1answer
166 views

Surface bound charge in the electric displacement

In Griffiths, the electric displacement is written with just volume charge density, and that is because, he says, 'we cannot apply gauss law precisely at the surface of a dielectric, for here volume ...
2
votes
1answer
212 views

Description of charged sphere with Heaviside function in cylindrical coordinates

I need to describe density of charge of uniformly charged sphere (radius R, total charge Q, position of centre (0,0,0)) with Dirac delta function and Heaviside step function. The hard part is to ...
2
votes
1answer
49 views

Induced motional EMF where the wire is stationary and the field source is moving?

If a wire is moving in a magnetic field $B$, there is a Lorentz force acting on both the postive and negative charges, separating them to create an electric field, which is a great explanation to aid ...
0
votes
1answer
191 views

Electric field inside coaxial cable

I have a very long coaxial cable with a cylindrical core of radius $a$ that has negative charge density $\rho = -k/r$ where $r$ is the distance from the axis of the cylinder, and an outer shell of ...
1
vote
4answers
5k views

Why is water not used as a dielectric in the condenser?

The dielectric constant of water is very high. Then why is it not used as a dielectric in the condenser?
0
votes
0answers
20 views

triboelectric effect at a liquid-liquid boundary?

In reading up on the triboelectric effect, most experiments deal with solid-solid interfaces. I've found some studies regarding solid-liquid boundaries, and even some engineering manuals outlining the ...
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votes
2answers
60 views
1
vote
1answer
44 views

Why don't charges build up on wires like plates of a capacitor?

Suppose you have a parallel plate capacitor and you want to charge it by using a battery. You will connect the plates with the two terminals of the battery. Now my book says that the charges will get ...
3
votes
3answers
13k views

Electric field of a negative charge

How was it discovered that the electric field of a negative charge points towards the charge itself? Is it true? (Courtesy of wikipedia)
5
votes
7answers
20k 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?
3
votes
2answers
53 views

Theoretical questions regarding the electric field

I found some theoretical questions in an old test of my school, and would like some help with the ones I cant answer: It is said that the electric field is an intermediary of the electric ...
3
votes
1answer
53 views

How to set up line integral of electric field? Confused over notation

In multivariable calculus the line integrals was parameterized and denoted: $$ \int_C \mathbf{F} \bullet \, d\mathbf{r}=\int_D\mathbf{F}(\mathbf{r}(t)) \bullet \frac{d \mathbf{r}(t)}{dt} \, dt $$ ...
1
vote
0answers
44 views

Refraction of the electric field lines, at the interface of separation between two conductive media

Suppose we have 2 media with electrical parameters ${\varepsilon _1},\,{\sigma _1}$, respectively ${\varepsilon _2},\,{\sigma _2}$, separated by the plane surface $\Sigma $; electrical charge surface ...
4
votes
2answers
98 views

Why doped silicon does not undergo electrostatic discharge?

Doped silicon is charge neutral overall, but since the extra added carriers are only weakly bounded (~45meV) they become delocalized. Since the concentration of silicon is 5-9 orders of magnitude ...
0
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2answers
170 views

Two different electrostatic charges in rotation

It's a theoretical problem. I mean I drawn a circle and I consider this circle exist. I would like to understand how works this device composed of a circle and two charges: Two charges fixed on a ...
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votes
1answer
23 views

Connecting spheres of different capacitance

If I connect a sphere of capacitance $C_1$ to a charged sphere of capacitance $C_2$, will the charge be distributed evenly on both spheres (is the charge density going to be equal on both spheres?). ...