Two cylindrical bars, each with diameter of 2.00 cm, are welded together end-to-end. One of the original bars is copper and is 0.390 m long. The other bar is gold and is 0.195 m long. What is the resistance between the ends of the welded bar at 20 oC ?
Look up the volume resistivities ρ of Cu and Au. For each bar, R ρL/A, where L is length and A is cross-section area. For this series-connected setup, R(total) is the sum of the two R values. Resistance at 20 oC of Cu 1.724 and Au 2.24 Since the diameter 2 cm, the A pi 3.14159 R((2.24)(.39)/pi) + ((1.724)(.195)/pi) R 0.278 + 0.107 0.385
