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## Homework Statement

Two infinite coaxial metal cylindrical tubes of radius a and b (a < b) are charged

with charge per unit length (unit [C/m]) [tex]\lambda[/tex] and [tex]-\lambda[/tex] respectively.

Calculate the electric field between the tubes (i.e. for a < r < b)

Where [tex]\epsilon_{0}[/tex] is the permittivity of free space

**2. The attempt at a solution**

Considering a Gaussian surface with radius R & length L where a < R < b, we can use Gauss' law to find the enclosed charge;

[tex]\oint \vec{E}. d\vec{a} = \frac{ q_{enc}}{\epsilon_{0}}[/tex]

This can then be rewritten as;

[tex]\oint \vec{E}. d\vec{a} = \frac{\lambda L}{\epsilon_{0}}[/tex]

Then I have no clue of where to go. Can take the magnitudes of the vectors and take the E outside or do i have to do something different?

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