Your professor gives you a summer job organizing his lab. On the first day, you

Question

Your professor gives you a summer job organizing his lab. On the first day, you come across three identically shaped cylinders of metal, each having a diameter of 5.19 mm and a length of 7.87 cm. They appear to be made out of different metals, but they are not labelled! They are, however, packaged with a table of the conductivities of several metals. You locate a multimeter and use it to measure the electrical resistance of each cylinder. Using the measured resistances and the table of conductivities, identify the metal that each cylinder is composed of. Sample 1: R1 = 2070 ?? Sample 2: R2 = 65.4 ?? Sample 3: R3 = 428 ??

Explanation / Answer

R1 :

rho = R A/L = 2070e-6*3.1416*(5.19e-3/2*5.19e-3/2)/0.0787 = 5.56e-7 ohms.m

R2 :

rho = R A/L = 65.4e-6*3.1416*(5.19e-3/2*5.19e-3/2)/0.0787 = 1.76e-8 ohms.m

R3 :

rho = R A/L = 428e-6*3.1416*(5.19e-3/2*5.19e-3/2)/0.0787 = 1.15e-7 ohms.m

Just look at the table of conductivities and identify the metals.

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