What Is the Charge Distribution p(rho) for This Electric Field?

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Homework Help Overview

The problem involves determining the charge distribution p(rho) from a given electric field E(r) using Gauss' law. The electric field is expressed in terms of a constant and an exponential decay function, and the tasks include finding the total charge and integrating the charge distribution.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of Gauss' law in both differential and integral forms to find the charge distribution and total charge. There is an attempt to calculate the divergence of the electric field and relate it to the charge density. Questions arise about the integration process and the correct interpretation of volume elements in spherical coordinates.

Discussion Status

The discussion is ongoing, with participants providing partial calculations and seeking clarification on specific steps. Some guidance has been offered regarding the divergence calculation and the integration limits, but there is no explicit consensus on the correct approach yet.

Contextual Notes

Participants are reminded to show their work in accordance with forum rules, and there is a focus on ensuring that the calculations align with the appropriate mathematical frameworks for spherical coordinates.

jajay504
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Homework Statement


The Electric field E produced by an unknown charge distribution p (rho) is E(r)= (constant)*((exp(-ar))/r^2)*(r_hat).
a.) Use Gauss' law in differential for to determine p(rho)
b.) Find the total charge q_tot by directly integrating p(rho), and show that it is 0.
c.) Find q_tot again, except this time use Gauss' law in integral form.
d.) Make a sketch of p(rho)

Homework Equations





The Attempt at a Solution

 
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According to the forum rules, you need to show some effort at working the problem yourself before you can receive help.
 
Hey! Sorry for that... I did some work but I got stuck.

I used divergence E = p/e0

a.) div E = (-a/r^2 - 2/r^3) * exp(-a*r) = p/e0. So I know what p is.
b.) Then I tried to integrate over p(rho) to get q_tot

q_tot = Integral [pdV]
I got --> exp(-a*r)/r^2 - 2*exp(-a*r)/r^3 = q_tot

I'm still trying to figure out what is this surface
 
vela said:
According to the forum rules, you need to show some effort at working the problem yourself before you can receive help.

Sorry for that! I put down the work I had
 
jajay504 said:
Hey! Sorry for that... I did some work but I got stuck.

I used divergence E = p/e0

a.) div E = (-a/r^2 - 2/r^3) * exp(-a*r) = p/e0. So I know what p is.
You calculated the divergence incorrectly. Look up the formula for the divergence in spherical coordinates. Your book should have a list of the various vector operators for different coordinate systems.
b.) Then I tried to integrate over p(rho) to get q_tot

q_tot = Integral [pdV]
I got --> exp(-a*r)/r^2 - 2*exp(-a*r)/r^3 = q_tot

I'm still trying to figure out what is this surface
It's not a surface; it's a volume. What is dV in spherical coordinates? What limits should you be integrating over?

Please show more details of your work.
 

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