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**1. Homework Statement**

A copper resistor has the shape of a cylindrical shell. What is the resistance of this resistor if its length is 1m, its inner radius is 0.1cm, and its outer radius is 0.2 cm? What is the radius of a solid wire of circular cross section with the same length and the same resistance?

**3. The Attempt at a Solution**

R = int(dR)

dR = (rho)dr / (2(pi)Lr)

R = int((rho)dr / (2(pi)Lr), from r1 to r2)

R =(rho)dr / (2(pi)L) * ln(r2/r1)

With the given info, I came to a resistance R of 1.8 x 10^-8 ohms, equivalent wire radius 0.55m, but apparently the correct answer is 1.8 x 10^-3 ohms, equivalent wire length 0.17 cm. I'm not sure what I'm doing wrong.

Thanks for the help again, guys!