I used the equation E = lambda / (2 * pi * epsilonknot * r)
With epsilonknot = 8.85 * 10^-12, and r = .003m
When I used it, however, I wasn't sure what value to use for lambda, the linear charge density, so I think the problem may lie in there.
Thank you very much, by the way. :)
There lies a section through 2 long concentric cylinders of radii 4.5 and 8 cm. The cylinders have equal and opposite charges per unit length of 2 C/m. Along the common axis runs a wire with an equal positive charge per unit length. Find E at a radial distance r = 0.3 cm.
I'm not exactly sure...