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NeedPhysHelp8

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## Homework Statement

Calculate the energy per unit length for two long coaxial cylindrical shells, neglecting end effects. The inner and outer cylinders have radii a and b, and linear charge densities λ and -λ, uniformly distributed on the surface, respectively.

**2. The attempt at a solution**

Alright so first thing I did was calculate the electric field in various regions using Gauss' Law:

i) for r<a E=0

ii) for a<r<b [tex] E=\frac{\lambda}{2\pi \epsilon r} [/tex]

iii) for r>b E=0

Now I'm not too sure how to find the energy per unit length: we have the formula [tex] E=1/2 \int \lambda V \ dl [/tex] so should I just find the potential V(r) then sub it into that equation?

I can find V(r) by [tex] \int E \ dl [/tex]