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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72 views
Electric field of a negative charge
Displacing something against the gravitational field, gains it potential energy. Moving something against the nature requires work. If the electric field of a negative source charge 'Q' points inward, ...
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2answers
216 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)
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1answer
89 views
Is it possible to charge a capacitor to any potential? Does it depend on the dielectric placed between them?
Is it possible to charge a capacitor to any potential? Does it depend on the dielectric placed between them? Or, are there other factors affecting it?
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0answers
69 views
Electric potential of a spheroidal gaussian
I'm looking for results that compute the electrostatic potential due to a spheroidal gaussian distribution. Specifically, I'm looking for solutions of equations of the form
$$
...
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4answers
554 views
Is there a deep reason why springs combine like capacitors?
I was solving a practice Physics GRE and there was a question about springs connected in series and parallel. I was too lazy to derive the way the spring constants add in each case. But I knew how ...
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1answer
61 views
how to find the diameter of this fuse? [closed]
A fuse blows if the current exceeds 1.0 A. It is made of material that melts at a current density
of 620A/cm2. What is the diameter of the wire, assumed to have a circular profile, in the
fuse?
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0answers
41 views
Force acting on cube's face [closed]
Let's consider a hollow cube. Its faces are uniformly charged with surface density
of charge = $\sigma$.
Authors of that problem ask to find:
1) Force acting on each face of cube from charge $q$ ...
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1answer
63 views
Electric charge and the distance
The strength of an electric field is: $E = 200\ \mathrm{N/C}$
The potential (of the test charge) is: $V = 600\ \mathrm{V}$
$\epsilon_r=1$
I need to calculate the distance between this point and the ...
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1answer
72 views
Should the electric potential of a positively charged sphere be negative?
Because the indefinite integral of the electric field results in a negative value? (As the function is proportional to $r^{-2}$?
I've got to be missing something... Help please!! Thanks!
Also, I ...
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0answers
63 views
Finding final charge distribution on capacitors on grounding
I am trying to solve the following problem on capacitors:
Here's the circuit
I have to find the total energy loss when all three switches are closed, and subsequent equilibrium attained.
I had ...
3
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2answers
75 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 ...
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1answer
50 views
Charging an object by induction
when charging a sphere by induction using a (-) charged object , and we put it to the right side of the sphere, electrons are pushed to the left side , so we ground the left side and the excess ...
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2answers
320 views
Using photons to explain electrostatic force
I am trying to understand the idea of a force carrier with the following example.
Let's say there are two charges $A$ and $B$ that are a fixed distance from each other. What is causing the force on ...
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1answer
106 views
How to positively charge an object with a power source? [duplicate]
How do you positively charge something consistently? By what mechanism could this be achieved?
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4answers
163 views
How does positive charge spread out in conductors?
I know that when there are excess positive charges in a conductor, for example, a metal sphere, the positive charges will spread out over its surface. However, I am confused about how this excess ...
2
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2answers
117 views
distance of electron from proton
An electron is projected, with an initial speed of $1.10 \times 10^5 \text{m/s}$, directly towards a proton that is essentially at rest. If the electron is initially a great distance from the ...
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votes
2answers
193 views
Ionized Depletion Region, Why aren't those charged being excited?
Ok so I understand the PN junction, and how when 2 Semiconductor materials are placed together the Electrons will jump into the Holes near the junction creating a Negatively Ionized Atoms on the ...
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0answers
76 views
Electric potential due to an infinite polarized sheet
I have an infinite plane (no thickness) with a uniform dipole density $\mathbf p = p \mathbf n$, with $\mathbf n$ being the normal to the plane. So the surface charge density is $\sigma = \mathbf p ...
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3answers
323 views
Where's the energy in a boosted capacitor?
Suppose I look at a parallel plate capacitor in its rest frame and calculate the electrostatic energy, $E$.
Next, I look at the same capacitor in a primed frame boosted in the direction perpendicular ...
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1answer
496 views
Gradient of the electric potential
I was wondering if for a point-like charged object, does the gradient of the electric potential point in the direction of maximum increase or maximum decrease of the function $V$?
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2answers
223 views
Electric potential at a point outside a charged sphere
The question asked me to find the potential at a distance $r$ from the center of a charged sphere, where $r>r_0$ of the sphere.
Actually, the question is answered, but what is confusing me is ...
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2answers
97 views
How can you calculate (or convert) the Wh of a capacitor whose energy is given in Farads
When trying to compare the energy in a battery to the energy in a capacitor, the units don't match up. How can one compare a battery whose Ah are 10 and Voltage is 3 (for a total of 30 Wh) to a ...
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1answer
114 views
The field of uniformly charged ball (without Gauss theorem)
The solution of Poisson equation is given by
$$
\mathbf E = \int \frac{\rho (\mathbf r )(\mathbf r_{0} - \mathbf r )}{|\mathbf r_{0} - \mathbf r|^{3}}d^{3}\mathbf r.
$$
I tried to use this term for a ...
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2answers
136 views
Electric lines of force
Why cant electric lines of force pass through the charged sphere? Well, basically that's how a Faraday cage works, but how can it be so?
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1answer
607 views
How can electric displacement vector field is equivalent to flux density on free space
Wikipedia states that
"In free space, the electric displacement field is equivalent to flux density, a concept that lends understanding to Gauss's law".
Doesn't that meant that at free space ...
2
votes
3answers
264 views
Maxwell Stress Tensor in the absence of a magnetic field
I'm having some trouble calculating the stress tensor in the case of a static electric field without a magnetic field. Following the derivation on Wikipedia,
Start with Lorentz force:
$$\mathbf{F} = ...
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3answers
128 views
Explanation on the resulting forces of two positive point charges
Why will the resulting force lines of two positive point charges be like this:
I would expect this:
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3answers
1k views
Can Laplace's equation be solved using Fourier transform instead of Fourier series?
Sorry for the long text, but I am unable to make my question more compact.
Any periodic function can be Fourier expanded. Usually, they say in mathematical physics books, if the function is not ...
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6answers
316 views
Is voltage electric potential or electric potential difference?
On Wikipedia, voltage is defined to be the electric potential difference. However, I am still not certain as to whether voltage is the electric potential ($PE/q$) or electric potential change ...
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1answer
67 views
How to make a nongrounded conductor have equipotential?
I'm studying the Method of Images and I seemed to have come to a conundrum. Method of Images takes advantage of grounded objects, (I am currently studying spheres), to set boundary conditions. ...
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1answer
130 views
Electric field singularities
Is this the list of all possible singularities in electrostatic field $E$?
near the point charge: $\frac{1}{r^2}$
near the line of charge: $\frac{1}{r}$
near the edge (not surface) of uniform ...
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0answers
166 views
Induced surface charge of conducting sphere, and energy?
Find the induced surface charge on a conducting grounded sphere as a function of the polar angle. The hint given is to integrate this charge density over the sphere to find the total induced charge.
...
2
votes
1answer
69 views
Electric force on spherical surface
I have a doubt about electrical forces on surfaces, for instance, on the surface of a sphere. I'll explain my point: let's say we have some spherical surface of unit radius and there's one point ...
4
votes
2answers
232 views
Why is electric potential scalar?
I can't conceptually visualize why it would be so. Say you have two point charges of equal charge and a point right in the middle of them. The potential of that charge, mathematically, is proportional ...
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1answer
44 views
Grounding insulative material
When grounded, can an insulative material keep its charge for any measurable length of time? Or, I suppose, if it was a perfect insulator, would it discharge at all?
An example might be a charged ...
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0answers
45 views
Semi-conductors and induced charge
Can a semi-conductor ( germanium or silicon) or a semi-metal ( graphite ) carry an induced charge ?
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3answers
195 views
Why can we use Gauss' law to compute electric field?
For simplicity I'm considering only the sphere case.
In the Gauss' Law formulation we have some field E introduced by charges $Q$ inside some sphere, then we compute flux and integrate, and we get ...
5
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6answers
768 views
Laplacian of $1/r^2$ (context: electromagnetism and poisson equation)
We know that a point charge $q$ located at the origin $r=0$ produces a potential $\sim \frac{q}{r}$, and this is consistent with the fact that the Laplacian of $\frac{q}{r}$ is
...
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1answer
35 views
Permanently charging a sphere by induction using a high voltage
I want to charge a sphere using a van de graff generator , it would sound easy , but using a 1 MV or a 900 KV is really hard, it is enough to break like 1 meter of air so whenever i try to ground the ...
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3answers
330 views
Is this really how a capacitor works? Why doesn't it behave like a resistor?
My book says a capacitor is two conducts being connected by an insulator. Now let's take a parallel plate capacitor to simplify the problem I have.
Suppose I got two parallel plate capacitor in ...
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1answer
123 views
Finding the electric field on a point (x,y,z) using Coulomb's Law
Using Gauss' Law, the answer is $$\frac{Q}{4 \pi \epsilon R^2}.$$
However if I were to do the integration using Coulomb's Law, I get
$$ \int_0^{2\pi} \int_{0}^{\pi}\int_r^a \frac{\rho \sin\theta dR ...
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0answers
65 views
Electric field singularity
What's a general proof for the log-singularity of electric field near the edge of a uniformly charged surface?
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2answers
239 views
A Question From Jackson Electrodynamics
I have a question regarding Jackson's Classical Electrodynamics. Consider the equation
$$\varphi \left ( x\right )=\tfrac{1}{4\pi\epsilon _{0}} \int_V \frac{\varrho ( x )}{R}d^{3}x+\tfrac{1}{4\pi} ...
2
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2answers
138 views
Electric field lines
If electric field lines cannot terminate in empty space, in the simple example of two equal charges what happens to the line starting from one of the charges toward the other in the middle?
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0answers
45 views
numerical investigation of stability [closed]
I am trying to find the required specifications of an paul RF trap, in which a proton can be confined.(trap dimensions,voltage frequency and amplitude used, etc). I have to solve the equations of ...
0
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1answer
144 views
Finding the electric field
The charge per unit length on a long, straight filament is -91.9 µC/m.
(a) Find the electric field 10.0 cm from the filament, where distances are measured perpendicular to the length of the ...
2
votes
2answers
2k views
Dirichlet and Neumann Boundary condition: physical example
Can anybody tell me some practical/physical example where we use Dirichlet and Neumann Boundary condition. Is it possible to use both conditions together at the same region?
If we have a cylindrical ...
2
votes
1answer
68 views
Electrostatic charge leakage
What are the ways electrostatic charged objects leak charge in humid conditions?
Can airborne particles pick up charge by contact, then be repelled hence removing charge? If so would it be a ...
3
votes
1answer
369 views
Electric Field due to a charged sphere
Suppose we have a spherical surface with a surface charge density varying as $cos(\theta)$. Apparently one can find the electric field both outside and inside such a spherical surface by superposing ...
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2answers
118 views
Calculate force of electric charges “suspended” by strings
In a question:
Two small plastic balls hang from threads of negligible mass. Each
ball has a mass of 0.110g and a charge of magnitude q. The balls are
attracted to each other, and the ...
