# Laplacian Coaxial Cable

1. Mar 27, 2008

### jesuslovesu

1. The problem statement, all variables and given/known data
If anyone could clarify this statement for me, I'm having a bit of difficulty interpreting what the heck I'm supposed to do:

"For a given potential difference V0 between the inner and outer conductors and for a given fixed value of b, determine the inner radius a for which the largest value of the electric field is a minimum."

I found the potential fairly easily using Laplace's equation
$$V(r) = \frac{V_0 ln(r/b)}{ln(a/b)}$$ (a is inner radius, b is outer)
I know that the electric field is the negative gradient of potential, but I really don't know what they are getting at.

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