Answer:
R = ρ L / A resistance of wire
ρC / ρA = [RC AC/ LC] / [RA AA/ LA} = AC / AA
Since resistance and length are the same for both wires where A is the area of the wire
ρC / ρA = rC^2 / rA^2 where r is the radius of the wire
(ρC / ρA)^1/2 = rC / rA
rC / rA = (1.72 / 2.83)^1/2
rC / rA = .780 radius of copper wire is .780 of aluminum wire
