All Questions
129
questions
-2
votes
0
answers
16
views
force on circular loop due to current in long wire [closed]
my first try is take element at a distance theta from R2 then write force equation and then integrate between -90 to +90 and similarly. but it is getting more complicated. anyone solve this question
0
votes
1
answer
33
views
Understanding Symmetries and Invariances in Electrostatic Fields [closed]
I'm currently studying electrostatics and I'm having trouble understanding the concepts of symmetries and invariances of electrostatic fields. I understand the basic definitions of symmetry planes and ...
3
votes
0
answers
52
views
Question about Fourier-coefficients in Griffith's Problem 3.15 (Electrodynamics) [closed]
I am having some trouble with problem 3.15 from Griffith's Electrodynamics. It states the following:
A rectangular pipe, running parallel to the $z$-axis (from $-\infty$ to $+\infty$), has three ...
- 49
0
votes
0
answers
31
views
Need help identifying missing boundary condition in charge transport problem
The system I am considering consists of a conducting liquid sandwiched between two electrodes.
The electrodes supply a constant flux of electrons $J_{ext}$.
In the liquid there are also uncharged ...
- 33
0
votes
1
answer
34
views
How to find the capacitance between two metal sheets [closed]
Let’s say I have two metal sheets in a 2D plane. The first one has area A, the second one is infinitely long, and they are separated from each other by a distance d. How can I find the capacitance ...
1
vote
1
answer
62
views
'Thin' conducting plate ambiguity
The situation at hand:
We have an infinite, thin conducting, grounded ($V=0$) plate at $z=0$.
Point charge (with charge +$Q$), at $z = a$.
How exactly are the charges distributed? I used the method ...
1
vote
1
answer
63
views
Derivation of the ring charge from a disk charge with a hole
I am doing a problem in which I am given a uniformly charged disk, charge density $\sigma$, with radius $b$ and a concentric hole of radius $a$ in the $xy$ plane. A part of the problem I would have to ...
- 11
-1
votes
1
answer
44
views
Is the strength of the charge equal on all points on an equipotential surface? [closed]
Since the equipotential is calculated by $V = q\cdot \frac{k}{r}$ I suppose that the charge is the same at any point on an equipotential surface but I'm not sure.
0
votes
1
answer
117
views
Point charge between two infinite dielectrics [closed]
Two infinite linear homogeneous and isotropic dielectrics $\epsilon_1$ , $\epsilon_2$, occupy the regions $z>0$ , $z<0$ respectively. A point charge q is located at the origin. By applying the ...
- 3
1
vote
1
answer
93
views
Prove that the electrostatic potential is zero (Wald) [closed]
Let $V$ be a bounded region of space and let $\phi $ be an electrostatic potential that is source free in this region, so that $\nabla^2 \phi=0$ throughout $V$. Suppose that $x$ is lying on the ...
- 76
0
votes
1
answer
47
views
Trying to find the magnetic force applied by an infinite wire on a circuit both carrying different currents
The problem I'm trying to solve is:
We have:
An infinite wire carrying the current I and creating the magnetic field: $\vec{B}(M) = \frac{\mu_0I}{2\pi\rho}\vec{e}_{\phi}$
A square shaped loop ...
0
votes
1
answer
125
views
Force exerted by the southern hemisphere of a uniformly charged sphere on the northern hemisphere
I understand that this question has been asked multiple times before but my question is regarding something specific.
I came across the following solution on the web:
Since $\vec{E}$ is the field at ...
- 1,638
0
votes
1
answer
109
views
Multipole expansion along a ring [closed]
I'm supposed to calculate the behavior of the electrostatic potential $V$ at large distances $|r| \gg a$ for the following linear charge density along a ring of radius $a$:
$$\rho(r,\psi, z) = \frac{q}...
- 287
2
votes
1
answer
854
views
What will happen to the bulb of the circuit after closing the switch? [closed]
Say it connects a bulb with the circuit below, with the switch $S$ open. Every cable has negligible resistance and the battery has no internal resistance.
What happens to the brightness of the bulb ...
- 23
0
votes
1
answer
29
views
What is the intuition for no resistance between concentric spherical surfaces if $k = 0$ in this problem? [closed]
I've currently solved problem 5.16 in Cheng's book on Field and Wave electromagnetics. The problem is stated as:
Determine the resistance between two concentric spherical surfaces of radii $R_1$ and $...
- 344
1
vote
1
answer
57
views
Determine the charge distribution and the total charge of the system [closed]
Suppose we have a spherical symmetrically distributed charge in vaccuum which yields us a spherically and symmetrical potential $V(r)$ according to:
$$V(r) = V_0(1-(r/a)^2)$$
for $r\leq a$ and $0$ ...
- 344
-1
votes
1
answer
92
views
No limits of integration for electric field integral?
For this problem,
The solution is,
However, why have they not included limits of integration? I think this is because all the small charge elements dq across the ring add up to Q.
However, how would ...
- 49
0
votes
1
answer
563
views
Electric field in a center of a tiny hole cut out in a hollow sphere [closed]
Suppose we have a hollow sphere charged uniformly with
a surface charge density σ. A circular hole is cut out,
small compared to the radius R of the sphere. Find the electric field
in the center of ...
- 3
1
vote
1
answer
742
views
Force between two dipoles [closed]
I am extremelly confused with this question: Basically suppose we have two electric dipoles, parallel to each other, as follows in the figure:
I am supposed to show that the force is attractive and ...
- 980
1
vote
2
answers
272
views
Electrostatics Boundary condition for 2D problems [closed]
The 4 conditions above are what I am being taught, and I am aware of the usual boundary conditions of electric field and potential, but that links to surface charge density, and I was wondering how do ...
- 11
0
votes
2
answers
53
views
Electric field of a configuration of five parallel infinite slabs of dieletric materials [closed]
I am having a hard time trying to figure out how to proceed in order to calculate the electric field of a configuration of five slabs of dieletric (insulating) material (actually one of those is ...
0
votes
1
answer
28
views
What is the distribution of surface charge of the inner conductor of this system? [closed]
Given the following system, where the conductors (marked as yellow in the picture) have spherical symmetry. The inner conductor has $\textit{+Q}$ charge and the outer conductor has $\textit{-Q}$ ...
- 177
1
vote
1
answer
37
views
A confusing problem in electro- and/or magnetostatics: two parallel cylinders with opposite currents
I got the following problem as a part of my assignment in physics:
Equal but opposite currents $J$ flow on the surfaces of two cylinders of radii $R_1$ and $R_2$, respectively, with the axes of the ...
- 43
1
vote
2
answers
312
views
Conversion of 1D charge density to 2D charge density via integration
I'm self-studying EM (using the third edition of Griffiths) and have a quick question. Problem 2.41 states:
Find the electric field at a height $z$ above the center of a square sheet (side a) ...
- 684
0
votes
1
answer
239
views
Potential energy of two point charges of opposite sign (exercise)
I'm trying to do this exercise, but I don't understand how the textbook does it:
I don't understand, how they get a positive $27V$ and a got a few more doubts:
First thing, you can only measure ...
- 299
0
votes
3
answers
850
views
Right Hand Rule Help: Part 2
I’m confused about this problem with the right hand rule.
According the book:
My thumb should point up (as expected)
My fingers should point into the page (I don’t know how that would work)
My palm ...
- 113
3
votes
1
answer
94
views
Potential near a charged cylinder? [closed]
A non-conductive electrically charged cylinder of length $L$ and radius $R_o$ has a uniform charge distribution $q$.
What is the potential $V$ at the cap and bottom ($z=-L/2, z=+L/2$)? And at the ...
- 35.4k
2
votes
0
answers
61
views
Work required to bring point charge towards conducting planes [closed]
Consider the following configuration: A point charge sits in the upper right $(x>0,y>0,z)$ space. The other quadrants are separated by two conducting planes in the $(x=0,y,z)$ & $(x,y=0,z)$ ...
- 329
-1
votes
1
answer
38
views
Eletrical Field created by a charge surface on a point [closed]
I was answering this question and even tho i know intuitively that the radial component of the eletric field will cancel out by simmetry, i could not get that in the integral calculation. I´m asking ...
2
votes
1
answer
262
views
Conducting sphere in uniform field held at zero potential [closed]
The set up is "A conducting sphere of radius $r_0$ is placed in an originally uniform electric field E, and maintained at zero potential. Show that the potential outside the sphere is:
$$\Phi(r,\...
- 21
0
votes
2
answers
191
views
I’m struggling with this question of gauss law application
I am confused with this question.What Gaussian surface do I take to calculate the electric field at the $q$ charge? Should it be a cylinder containing the whole system? Or should it be a cylindrical ...
- 125
2
votes
2
answers
162
views
Any boundary conditions missing from this problem? [closed]
Recently I was solving some boundary value problems in Electrostatics. I stumbled upon a problem with an infinitely long cylinder (axis along the $z$-direction and radius $a$) with a plate inside it (...
- 23
1
vote
0
answers
95
views
Soap bubble with air blown in and charge distributed [closed]
So, I was trying to do this question and here is my attempt:
I first tried work out the surface tension forces like so:
I did $ F= PA$
$ P = 4 \frac{\gamma}{r}$ by laplace law
so,
$ F = 16\gamma \pi ...
- 7,980
0
votes
1
answer
161
views
Electron Plasma Frequency
Displayed is the context
My question is, why doesn't the electric field from the electrons permeate throughout the cold plasma?
Surely there will be flux on the RHS of the boundary as there is an ...
- 268
0
votes
2
answers
228
views
Electric potential infinite box
I have a question about separation of variables to calculate the electric potential.
In the picture below the potential is only on the top of the box, which is infinite in the $z$-direction. What are ...
- 85
1
vote
2
answers
55
views
Electric field exerted by a ball with varying density
Say there's a ball with radius R. In $0<r<d$, the density is some $\rho_1(r)$ and in $d<r<R$, the density is $\rho_2(r)$. When I calculate the total charge enclosed in $d<r<R$, how ...
- 1,038
0
votes
0
answers
341
views
Electric field on the surface of dielectric sphere and outside sphere
Let a dielectric sphere of radius $r_0$ and permittivity $\epsilon_1$ is placed in medium of permittivity $\epsilon_2$. The electric field inside sphere is $\mathbf{E_1(\mathbf{r})} = E_0 \hat{z}$. ...
- 1,335
0
votes
1
answer
343
views
Electric field on a point at a height $z$ from the midpoint of a charged line [closed]
First let me say I have already read the thread Electric field a distance z above the midpoint of a straight line segment concerning the exact same problem I'm talking about. Nevertheless, my question ...
- 307
0
votes
1
answer
28
views
What distance do I use when examining the effect of an electric field on a point outside of a nonconducting sphere with an arbitrary volume charge?
It's easy enough for me to do this for a ring (as I interpret the field lines as "exiting from the centre of the ring") or a point (simply the distance from the point to the other point), but I just ...
- 19
1
vote
0
answers
42
views
Abstract approach to the total electric force on a charged rod
Suppose we have a 1-dimensional system (x-axis) consisting of rod of finite length $l$ and arbitrary charge density of $\lambda(x)$ at rest extending from the origin to $x=l$. And now, suppose we have ...
- 165
0
votes
1
answer
73
views
Electromagnetic waves, displacement currents and capacitors
Question:
Q. A parallel-plate capacitor having plate-area $A$ and plate separation $d$ is joined to a battery of emf $E$ & and internal resistance $R$ at $t=0$. Consider a plane surface of area
...
user220323
0
votes
2
answers
228
views
Null electric field at infinity? How? [closed]
Suppose there are two charges (4uC each) fixed in the horizontal axis. One is in x=0 and the other in x=8m.
I've obtained the electric field:
$E=-k\cdot4\mu C \cdot [\frac{1}{x^2}+\frac{1}{(x-8m)^2}]...
7
votes
2
answers
784
views
Approximating an expression for a potential
In a problem which I was doing, I came across an expression for the potential $V$ of a system as follows $$V = k\left(\frac{1}{l - x} + \frac{1}{l + x}\right)\tag{1}\label{1}$$ where $k$ is a constant,...
- 1,324
0
votes
1
answer
419
views
"dielectric constant" or "electrical permittivity"?
What are the differences between "dielectric constant" and "electrical permittivity"?
By searching on the net, I found permittivity = absolute permittivity, which is the measure of capacitance that ...
- 163
0
votes
2
answers
944
views
Expressing Maxwell's equations as scalar equations involving differentials in Euclidean space
I am trying to convert Maxwell's equations from the well known differential form (found on Wikipedia Maxwell's equations) into scalar equations involving partial derivatives (more than four equations)....
- 469
0
votes
1
answer
534
views
Principle of superposition in spherical shells
If I have a spherical shell with a uniform positive charge desnity on its surface is near a positive point charge q (sitting in quadrant II area)
In consideration of the electric field strength and ...
- 33
0
votes
1
answer
125
views
Capacitor with a spring [closed]
The plates of capacitor are attached with non conducting spring of spring constant k. The initial separation between the plates is d and the spring is relaxed initially. Now the charges +Q and -Q is ...
0
votes
1
answer
49
views
Decreasing energy but at expanse of what
question : A hollow spherical shell with radius R has charge Q uniformly distributed
over it.
(i) show that the energy
stored in this system is $\dfrac{Q^2}{8\pi \epsilon_{0}R}.$
(ii) Now imagine ...
user182868
3
votes
1
answer
446
views
Field at the center of a cube with positively and negatively charged faces [duplicate]
I'd like to share an interesting physics problem with the Physics SE community, one I found in a Russian Physics Olympiad Paper (without solution)
An insulating hollow cube of edge length $L$ has ...
- 1,921
2
votes
1
answer
2k
views
Potential due to a charged ring : Electric field discontinuity
I have just begun with my third year intermediate course in electrodynamics. A standard problem in electrostatics that one may repeatedly encounter is that of finding the potential due to a uniformly ...
- 380