Solving Electrostatic Potential of a Spherical Conducting Shell

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SUMMARY

The discussion focuses on solving the electrostatic potential outside a spherical conducting shell of radius R, held at a potential V0, with a specified charge density ρ(r) = ρ0sinθcosφ for R < r < 2R. The solution employs Green's function in spherical coordinates, incorporating Dirichlet Boundary Conditions to derive the potential Φ(r'). The participant seeks simplification in their approach, considering the use of a Gaussian surface to potentially streamline the calculations.

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  • Understanding of electrostatics and potential theory
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  • Knowledge of spherical harmonics and their applications
  • Experience with Dirichlet Boundary Conditions in electrostatics
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  • Explore simplifications in potential calculations using spherical harmonics
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Homework Statement


A spherical conducting shell of radius R is held at a potential V0. Outside the shell,
the charge density is ρ(r) = ρ0sinθcosφ for R < r < 2R. Find the electrostatic potential
everywhere outside the shell.

Homework Equations


Green's function in spherical coordinates between radii a < r < b:
G(r,r') = ##\sum\limits_{l,m} {\frac{4π/(2l+1)}{l-(\frac{a}{b})^{2l+1}} Y^*_{lm}(θ',φ')Y_{lm}(θ,φ)(r^l_< - {\frac{a^{2l+1}}{r^{l+1}_<}})({\frac{1}{r^{l+1}_>}}-{\frac{r^l_>}{b^{2l+1}}})}##

The solution for the potential using Green's function with Dirichlet Boundary Conditions (V is the Volume, S is the boundary surface, n is the normal to the surface):
##Φ(\textbf{r'} ∈ V) = {\int\limits_{V} d\textbf{r} ρ(\textbf{r})G(\textbf{r',r})} - ε_0 {\int\limits_{S} R^2 \: dΩ \: V (\textbf{r}){\frac{∂G(\textbf{r',r})}{∂n}}}##

The Attempt at a Solution


I know the potential at the boundary surface:
## Φ_{S}(\textbf{r}) = V_0 ## where r = R

The normal direction on the surface is r, a = R, b = 2R, so:
at r = R, ## {\frac{∂G(\textbf{r',r})}{∂n}} = \sum\limits_{l,m} {\frac{4π/(2l+1)}{l-(\frac{1}{2})^{2l+1}} Y^*_{lm}(θ',φ')Y_{lm}(θ,φ)((2l+1)R^{l-1})({\frac{1}{r'^{l+1}}}-{\frac{r'^l}{R^{2l+1}}})} ##

The charge density can be expressed using spherical harmonics:
## ρ = ρ_0 {\frac{1}{2}} {\sqrt{\frac{8π}{3}}} (Y_{1,-1}(θ,φ) - Y_{1,1}(θ,φ)) ##

So:
##Φ(\textbf{r'}) = {\int\limits_{Ω}}{\int\limits_{R}^{2R}} r^2 dr \: dΩ \: [ ρ_0 {\frac{1}{2}} {\sqrt{\frac{8π}{3}}} (Y_{1,-1}(θ,φ) - Y_{1,1}(θ,φ)) ] ## ...
... ## [ \sum\limits_{l,m} {\frac{4π/(2l+1)}{l-(\frac{1}{2})^{2l+1}} Y^*_{lm}(θ',φ')Y_{lm}(θ,φ)(r^l_< - {\frac{R^{2l+1}}{r^{l+1}_<}})({\frac{1}{r^{l+1}_>}}-{\frac{r^l_>}{(2R)^{2l+1}}})} ] ## ...
...##- ε_0 {\int\limits_{S} R^2 \: dΩ \: V_0 \: \sum\limits_{l,m} {\frac{4π/(2l+1)}{l-(\frac{1}{2})^{2l+1}} Y^*_{lm}(θ',φ')Y_{lm}(θ,φ)((2l+1)R^{l-1})({\frac{1}{r'^{l+1}}}-{\frac{r'^l}{R^{2l+1}}})} }##

Am I barking up the wrong tree? I am looking for some key simplification. Maybe my approach is over-complicating it, and I should use a Gaussian surface. The issue with that is that I don't see where the electric field would be constant, leading to a simplification.
 
Last edited:
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Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
 

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