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Maximum potential (coaxial cable)

by weesiang_loke
Tags: cable, coaxial, maximum, potential
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Mar23-11, 08:32 AM
P: 33
1. The problem statement, all variables and given/known data
Given a coaxial cable with outer conductor of radius b, and inner conductor of radius a. Prove that maximum potential is obtained when a = b /e, e is base of natural log.

2. Relevant equations
gauss law, ...

3. The attempt at a solution
By using Gauss Law,
for a < r < b,
i have E = 2*k*[tex]\lambda[/tex] / r, where [tex]\lambda[/tex] = Q/L

then the potential difference, V= [tex]\int[/tex] E dr
V = 2*k*[tex]\lambda[/tex] ln (b/a),

but i am not sure how to continue by differentiating V wrt a.
Help me pls...
Thank you.
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Mar23-11, 08:47 PM
P: 33
Anyone pls help ......

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