All Questions
28
questions
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Interpretation of Equation of energy stored in continuous charge distribution [duplicate]
In the book "Introduction to Electrodynamics" by David J. Griffiths, $\boldsymbol\S$ 2.4.3$\blacksquare $ The Energy of a Continuous Charge Distribution, I came across this equation for ...
1
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3
answers
398
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Deriving energy in Dielectrics
Note: I am working in the Lorentz-Heaviside system and all the integrals are over the whole space.
Definitions:
$$\vec E= \vec E_f+\vec E_b$$
$$\phi=\phi_f+\phi_b$$
$$\vec D=\vec E+\vec P$$
$$\rho=\...
0
votes
2
answers
411
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Is energy infinite in an electric field?
Energy is defined as the capacity to do work. Work in turn is defined as force x displacement.
An electric field exerts the field in all directions infinitely (even though the strength of that force ...
- 11
0
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1
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132
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Different result when deriving electric force as $dW/dr$ and $-dU/dr$
Work done by electric field, $W$ is the negative of the change in electric potential energy, $U_r$.
$$W=-\Delta U$$
By considering an infinitesimal change in EPE, we can deduce that electric force, $...
- 113
0
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1
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213
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Electric Potential, Work, Potential Energy, and Electric Field [closed]
I don't quite understand these concepts. What is the relationship of electric potential with work, potential energy, and electric field?
0
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3
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170
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Why is the force that does the work, when calculating the electric potential energy, symmetric to the electric force? [closed]
"The electrical potential at a point is the work per unit charge required to move the charge to that point (r) from another point which has been assigned a potential of zero ($r_{0}$)". This ...
- 169
0
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2
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66
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Question about the sign of $\mathbf{E}\cdot d\mathbf{l}$ when computing the Electric Potential [duplicate]
I have a question on the derivation of the electric potential for a single charge located at the origin.
The electric potential is defined as $$V\left(\mathbf{r}\right)=-\int_{\mathcal{O}}^{\mathbf{r}}...
- 313
2
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2
answers
174
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I really don't understand the sign Work and energy in an electric field
This might be a super simple question to answer but I can't find one that makes sense to me and I feel like I am getting conflicting answers. I have always thought that positive work means that the ...
- 23
1
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2
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277
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Does an infinite wire of charge have an infinite potential energy per unit length?
I was doing a physics problem in Purcell's E&M book when I encountered a problem that asked to find the work needed per unit length to assemble an infinite wire charge of radius $a$, by bringing ...
- 23
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2
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531
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Is the (electrostatic) interaction energy always positive, or can it be negative? [duplicate]
We know that work done $W$ to assemble $q_1$,...,$q_n$ point charges is
$$
W = \frac{1}{2} \sum_{i = 1}^{n} q_i V(r_i) \tag{I}
$$
Now for the continous charge distribution with charge density $k$, we ...
- 103
1
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2
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80
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How to make sense out of Potential Energy?
My teacher says that Energy is in the form of Electric field. I've also seen the mathematical prove. (The amount of work done in bringing a charge from infinity to that point in the Electric Field) ...
- 63
1
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0
answers
133
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Work $U$ required to assemble a charge distribution
I'm reading Purcell's Electricity and Magnetism (p. 72) and it gives an relation between the work $U$ required to assemble a charge distribution $ \rho (x,y,z) $ and potential $\phi (x,y,z) $ of that ...
- 159
2
votes
4
answers
491
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How can we have negative work in electrostatics, if $W=(\epsilon_0/2)\int\! E^2\ \mathrm{d}\tau$?
This question is motivated by Section 3.2.3 in Griffiths.
Therein, we are considering the force of attraction between a point charge and an infinite conducting plane. One can calculate the field ...
0
votes
2
answers
108
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Why is $U_e=-W$?
Electric potential energy $U_e$ is defined as $k_e\frac{Q_1Q_2}{r}$. From that we get:
$$U_e=k_e\frac{Q_1Q_2}{r}=ErQ_2=F_er=W$$
Now, a lot of sources claim that $U_e=-W$. Why is work negative in this ...
- 167
1
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2
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420
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Energy stored in an electric field
I know the mathematical proof that $U=\frac{\epsilon_0}{2}\int\vec{E}^2dv$ is the energy stored in a particular volume in space due to an electric field, but I don't get what it actually means. I lack ...
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