Deriving Electric Field for a Conductor-Shell System using Gauss's Law

[chillaxin]

A long straight conducting rod (or wire) carries a linear charge density of +2.0uC/m. This rod is totally enclosed within a thin cylindrical shell of radius R, which carries a linear charge density of -2.0uC/m.
A) Construct a Gaussian cylindrical surface between the rod and the shell to derive then electric field in the inner space as a function of the distance from the center of the rod.
B) Construct a Gaussian cylindrical surface outside both the rod and the shell to calculate the electric field outside the shell.

This is what i have so far.

E=q/4piEor^2
E=+2.0uC/m / 4pi8.85x10^-12(-2uC/m)^2
E=4.5x10^9Nm^2/C

 

[Andrew Mason]

A long straight conducting rod (or wire) carries a linear charge density of +2.0uC/m. This rod is totally enclosed within a thin cylindrical shell of radius R, which carries a linear charge density of -2.0uC/m.
A) Construct a Gaussian cylindrical surface between the rod and the shell to derive then electric field in the inner space as a function of the distance from the center of the rod.
B) Construct a Gaussian cylindrical surface outside both the rod and the shell to calculate the electric field outside the shell.

This is what i have so far.

E=q/4piEor^2
E=+2.0uC/m / 4pi8.85x10^-12(-2uC/m)^2
E=4.5x10^9Nm^2/C

It asks you to apply Gauss' law:

$$\oint E\cdot dA = \frac{Q_{encl}}{\epsilon_0}$$

If you pick a gaussian surface through which you know E is constant due to all points on the surface being equidistant from equal charges, the integral is simply

$$E\cdot A = \frac{Q_{encl}}{\epsilon_0}$$

Pick a surface that is inside the cylinder that fits that description and do the calculation.

AM