1. The problem statement, all variables and given/known data Two long concentric cylinders of radii .04 m and .08 m are separated by aluminum. The inner cylinder has a charge per unit length of [itex] \Lambda [/itex] at any time. When the two cylinders are maintained at a constant potential difference of 2 V via an external source, calculate the current from one cylinder to the other if the cylinders are 1 m long 2. Relevant equations potential difference = IR R = pl / A I = dq/dt J = I/A J = neV E = pJ 3. The attempt at a solution So my first attempt I used: potential difference = IR (2 V ) / (R) = I (R) = pl / A length is 1 meter I took area by pi(r)^2 outside - pi(r)^2 inside, pi(.08)^2 - pi(.04)^2 , .020 - .005 = .015 m^2 p is given in the book, p for aluminum is 2.655x10^-8 plugging in, R = 1.77 x 10^-6 so (2 V) / R = I (2 V ) / (1.77 x 10^-6) = 1.1 x 10^6 But my answer is way off from my books, with the answer being: 6.8 x 10^8 A What did I do wrong? I think the lambda at the beginning is a hint and that I might have to use Guass law?? My next thought was: E according to gauss law = (lambda)/(2pi\epsilon0r) E/p = J J * A = I but how am I suppose to get a value for lambda?? sorry that part gets me mixed up :/ Can anyone comment on which method they think is leading me to the right direction? Also something I might be doing wrong??