Two cylindrical bars, each with diameter of 2.30 cm, are welded together end-to-end. One of the original bars is copper and is 0.320 m long. The other bar is platinum and is 0.155 m long. What is the resistance between the ends of the welded bar at 20 oC ?
R ρ * L / A Resistivity copper at 20 C------ρ 1.68 10^-8 (ohm m) Resistivity platinium at 20 C--- ρ 10.6 10^-8 (ohm m) A π r^2 3.14159 * 1.15 ^2 4.15475 cm2 4.15475 10^-4 m2 R 1.68 10^-8 * 0.32 / 4.15475 10^-4 + 10.6 10^-8 * 0.155 / 4.15475 10^-4 R 0.1294 10^-4 + 0.3955 10^-4 0.52485 10^-4 Ω 0.000052485 Ω hyperphysics.phy-astr.gsu.edu/hba. Goodbye
