0
votes
1answer
53 views

The “classical radius” of the electron [on hold]

According to one theory, the mass m of the electron arises simply as a consequence of the electrostatic energy of its electric field, through Einstein's famous expression ε=mc^2, where ε is the field ...
0
votes
1answer
33 views

Net Electric Field of Multiple Charges [on hold]

Question: Four charges, each of magnitude +Q are placed at the corners of a square of side a. Obtain an expression for the electric potential at the centre of the square and at the mid point of one ...
1
vote
1answer
31 views

Show the equivalence of two electrostatic energy

$$U = \frac{1}{2}\iint_{all space}^{ } \frac{\rho(1)\rho(2)}{4\pi\epsilon_{0}r_{12}}dV_{1}dV_{2} $$ and $$U = \frac{\epsilon_{0}}{2}\int_{allspace}^{ } \vec{E} \cdot \vec{E} dV.$$ In the left ...
1
vote
0answers
24 views

Electric field of Symmetric Parts [closed]

So I'm preparing for a test and one thing that I haven't seen examples of, but know is possible is using Gauss's Law on objects that have symmetric parts. I made up the following question: Find ...
0
votes
0answers
30 views

Vector of electric field

I have a triangle whose points are in $A(0,0,0)$, $B(a,0,0)$ and $C(0,a,0)$. The edges of this triangle are uniformly charged with value $Q'$ and everything is in vacuum. I need to find the vector of ...
1
vote
3answers
48 views

Finding charge density from from differential form of gauss law

I didnt get why he didvided and multiplied by r^2.This question is from d j griffith .
1
vote
3answers
51 views

Potential due to a continuous charge distribution on ring

Derive the formula for the potential at point $P(0,0,z)$ directly above the center of a ring of charge with radius $R$ and uniform charge density $\lambda$. My attempt: Since $$\lambda= ...
2
votes
0answers
73 views

Differential equation of a Green function for a dielectric with a charge [closed]

adding Suppose there are two infinite planes, one in $z=a$ and the other in $z=b$, with $a<b$. Between the planes, there is a dielectric medium with constant $\epsilon_1$. The differential equation ...
1
vote
1answer
67 views

Zero divergence of Electric field

I'm trying to rigorously derive the integral form of Gauss's law from Coulomb's law and the divergence theorem. Arrive at $$ \oint\limits_{\partial V} E\cdot da = \begin{cases} \frac ...
1
vote
1answer
29 views

Help regarding understanding derivation of electrostatic potential in a solution to a problem

I was looking at the solution of finding the energy stored in a charged solid sphere in which the electric field was and then later stated the electrostatic potential is I understand that to ...
0
votes
1answer
21 views

2 spheres both negative or positive [closed]

Two small charged metal spheres A and B are situated in a vacuum. The distance between the centres of the spheres is 12.0 cm, as shown in Fig. 4.1. The charge on each sphere may be assumed to be a ...
0
votes
1answer
17 views

Two uniformly charged spheres are superposed with slight displacement. What's the surface density?

*Note: This is from the Second Volume of Feynman's Lectures on Physics : Mainly Electromagnetism and Matter And this is the excerpt from the book: If the relative displacement of the two spheres ...
2
votes
2answers
52 views

Is a given charge density a surface charge density or volume charge density?

The exact question goes like this: In a certain electronic tube, electrons are emitted from a hot plane metal surface, and collected by a plane metal plane parallel to the emitter, at a distance ...
0
votes
1answer
33 views

Image charge method to find electric field [closed]

The following is a question from my tutorial on boundary value problems and image charge method- A point charge +q is placed at (0, 0, d) above a grounded infinite conducting plane defined by z = 0. ...
2
votes
1answer
43 views

Electrostatic Potential Energy Integral

I'm trying to calculate the total energy of a simple two charge system through the integral for electrostatic energy of a system given in Griffiths' book: $$U = \frac{\epsilon_0}{2}\int_V E^2 dV .$$ ...
1
vote
3answers
49 views

Is there a place on the equipotential surface where a charge feels no electric force? [closed]

I'm given a graph of an equipotential surface where I need to find a place where a charge feels no electric force. I feel like it will be where the voltage is zero, which would be 2G on the graph, ...
2
votes
1answer
43 views

Find the field of two infinite strips of width $b$ [closed]

Q:The two charged strips in the following picture have width $b$, infinite height,and negligible thickness(in the direction perpendicular to the page).Their densities per unit area are $\sigma$ ...
0
votes
1answer
45 views

Potential Differences (Voltage) from Point Charges [closed]

Identical +1.8 micro Colomb charges are fixed to adjacent corners of a square. What charge (magnitude and algebraic sign) should be fixed to one of the empty corners, so that the total electric ...
1
vote
2answers
53 views

Draw the charge configuration according to the electric field [closed]

I'm trying to draw the charge configuration outside the regions that lead to the given electric field patterns. Can someone show me how?
1
vote
0answers
35 views

Laplace's equation with spherical, cylindrical, and planar symmetry [closed]

Find the general solution to Laplace's equation for spherical symmetry (everything can only depend on $r$, the radius), cylindrical symmetry (everything can only depend on $s$, the radius), and ...
2
votes
2answers
90 views

Charge outside Gaussian Surface doesn't contribute to Flux?

I roughly understand the explanation for this: any electric field line that enters the surface, must leave it, since field lines can't terminate abruptly in space. My question is, what if you have a ...
0
votes
2answers
38 views

Net Electrostatic Field inside a Conductor is $\vec{0}$

I've heard an explanation for this, and my professor wasn't really able to clarify my questions, so I was hoping someone could help: Suppose there is an electrostatic field $\vec{E_{net}}\ne\vec{0}$, ...
0
votes
2answers
42 views

Find net force on a mass centered between four other masses

I'm not going to post the full question, I just want a general idea of how I should go about solving this type of problem. There is a square with 4 charged masses on each of the corners, in the ...
0
votes
0answers
41 views

Capacitance changes by a factor of 3 or 9?

This is an example problem with solution in a book I am reading on electrostatics. "We have two square parallel plate capacitors with length $a$ and separation $d$ with $d<<a$. If we triple ...
-1
votes
1answer
36 views

Electric Field of a sphere

Is there a point in space where the electric field is half of the electric field on the surface of the sphere? I just got curious if it would be possible.
0
votes
1answer
128 views

Coulombs law: calculate force exerted on one charge by the other two [closed]

The drawing shows three point charges fixed in place. The charge at the coordinate origin has a value of q1 = +8.00 μC; the other two charges have identical magnitudes, but opposite signs: q2 = ...
0
votes
1answer
39 views

Electrostatics Equilibrium problem [closed]

What should be the value of Q? I am doing the basics of coulomb's law,can anyone explain this to me?
0
votes
2answers
157 views

How can I split a resultant force into its $x$ and $y$ components?

Point charge 3.5μC is located at x = 0, y = 0.30 m, point charge -3.5μC is located at x = 0 y = -0.30 m. What are (a)the magnitude and (b)direction of the total electric force that these charges ...
3
votes
4answers
240 views

How can I calculate the force that is applied on a tube by another tube?

Let's say there is two tubes(cylinders with no tops or bottoms) with charges $q_1$ and $q_2$, radii $b_1$ and $b_2$, lengths $l_1$ and $l_2$. These tubes are located along the axis of each other's ...
1
vote
1answer
59 views

How to find the electric field of a charged tube?

Let's say there is a charged tube(cylinder with no top or bottom) with radius $a$, length $l$ and charge $q$ and a point which is collinear with the centre of the charged tube. Anyway, since we can ...
1
vote
0answers
71 views

How to calculate the electrostatic force between two dielectric rings of charge?

Let's say there is a dielectric ring of charge with radius $a$ and charge $q_1$. I could calculate the electrostatic force applied on a point charge with charge $q_2$ and which is collinear with the ...
1
vote
0answers
10 views

How to calculate the electrostatic force applied on an object that is along the axis of a charged tube's surface?

Let's say there is a charged tube(a cylinder with no top and bottom) with radius r and length l, charge q1 which also made out of insulating material. And also if there is an object with charge q2 ...
1
vote
0answers
36 views

How to calculate the electrostatic force applied on an object that is along the axis of a charged tube?

Let's say there is a charged tube(a cylinder with no top and bottom) with radius r and length l, charge q1 which also made out of insulating material. And also if there is an object with charge q2 ...
1
vote
1answer
136 views

Two spherical cavities hollowed out from the interior of a conducting sphere. At the center of each cavity a point charge is placed

From Griffiths: Two spherical cavities, of radii a and b, are hollowed out from the interior of a (neutral) conducting sphere of radius R. At the center of each cavity a point charge is placed – ...
2
votes
1answer
68 views

How can I apply to the differential form of Gauss' Law? [closed]

I'm trying to learn Maxwell's equations but I got stuck. I couldn't understand the usage of the differential form of the Gauss' law. How can it be applied to questions? For example, let's say there is ...
1
vote
1answer
55 views

How to calculate the force between line of charges?

As far as I know Coulomb's law only works for point charges but what if there are not any point charges? For example, let's imagine there are three rectangles with different sizes. First one is 50 cm, ...
0
votes
1answer
230 views

Electric field strength at the center of an equilateral triangle

Questions: Three $x$ m long rods form an equilateral triangle. Two of the rods are charged to $+q$ C and the third to $-q$ C. What is the electric field strength at the center of an equilateral ...
1
vote
0answers
66 views

Sign error in calculating the electric field of point charge

I have to determine the electric field of a point charge, I get a true result except for a sign. Here is my passages. $$\nabla \cdot e = \frac{\rho}{\epsilon}$$ $$e = - \nabla u$$ $$\nabla^2 u = - ...
1
vote
1answer
49 views

Flaw in the radius of a spherical electron model (classical electron radius)

My textbook asks me to derive an equation for the potential energy ($U$) of sphere ($r_0$) filled with an electric charge of uniform density ($\rho$), expressed in terms of the total charge $Q$. The ...
1
vote
3answers
125 views

Variation - Electric pressure on a sphere?

I solved the following question(Answer is correct): Find the force with which two hemisperical parts of a uniformly charged hollow sphere repel each other?(charge density: +$\sigma$) Answer: ...
0
votes
1answer
88 views

Minimum separation problem

I am trying to solve this problem where two point charges are infinite distance apart(horizontally) but separated by some finite distance vertically. Both are positively charged and projected ...
3
votes
3answers
176 views

How to solve the Laplace Equation in the hollow square region?

Suppose the values of $a$, $b$, $V_1$ and $V_2$ is given. I want to find the solution of the Laplace equation, $$\frac{\partial^2 \phi}{\partial x^2}+\frac{\partial^2 \phi}{\partial y^2}=0$$ in the ...
1
vote
1answer
182 views

How is capacitance of a cylindrical capacitor calculated?

I've just begun learning capacitance, and my lecture notes have a section on calculating capacitance for capacitors in vacuum of various shapes, e.g. two parallel plates and concentric spherical ...
0
votes
1answer
45 views

Maxwell calculations that predicted the generation of waves (further use for wireless telegraphs)

At this point in this documentary about the history of electricity: https://www.youtube.com/watch?v=oPnS2WO2_0k&t=4m40s the guy says the Maxwell calculations predicted the generation of certain ...
1
vote
0answers
45 views

Why a transistor is activated when I touch its base with my finger? [closed]

Is my body charged eletrically? If so, how much? Will it work with all types of transistors?
1
vote
0answers
31 views

Dipole charge attractions while one of them is turning around other [closed]

There is a electric dipole which is fixed. So angular momentum isn't conserved. And there is charge $Q$ which has initial velocity $u$. My question is: What is the tangential velocity of the charge ...
1
vote
2answers
70 views

Electric Potential of a sphere given electric field

I'm studying for a course in electromagnetism, and I've been given an electric field for which I need to find the associated scalar potential. The field is the field generated by a sphere of radius ...
0
votes
1answer
38 views

Potential in the middle of a square [closed]

Find the electric potential in the middle of a square with side length $a$ and charge $Q$. If I put the origin in the middle of the square, for the potential I get: ...
0
votes
1answer
105 views

Total number of electric field lines coming out of a proton?

I have to calculate the total number of electric field lines through a proton. I tried using Gauss' Law, i.e, $$\phi = \oint\boldsymbol E.d\boldsymbol s = {\frac{q}{\epsilon_0}} $$ $$So, \phi = ...
1
vote
1answer
80 views

Which symmetry for which distance function

For evaluating the electric field of some charge distribution one can use $$\phi(r):= \frac{1}{4 \pi \varepsilon_0}\int_{\mathbb{R}^3} \frac{\rho(r')}{||r-r'||_2} dr'.$$ My question is: What symmetry ...