Question

A gold wire is 4.5 m long and 0.45 mm in diameter. What is its resistance?

(The sheet from my professor.)

TABLE 21-1 Resistivities Substance Insulators Quartz (fused) Rubber Glass Semiconductors Silicon* Germanium* Conductors Lead Iron Tungsten Aluminum Gold Copper Copper, annealed Silver Resistivity, p (2 m) 7.5 × 1017 1 to 100 x 1013 1 to 10,000 x 109 0.10 to 60 0.001 to 0.5 22 × 10-8 9.71 × 10-8 5.6 x 10-8 2.65 × 10-8 2.20 x 10-8 1.68 × 10-8 1.72×10-8 1.59 × 10-8

Answer 1

Length of gold wire (L) = 4.5 m dia of wire (d) = 0.45 mm = 0.45 times 10^-3 m From the data sheet give, resistivity of gold is rho = 2.20 times 10^-18 Ohm m therefore we know the resistance formula as R = rho l/A = 2.20 times 10^-8 times 4.5/pi/4 times 6.45 times 10^-3)^2 R = 0.622472 Ohm