Question

On your first day at work as an electrical technician, you are asked to determine the resistance per meter of a long piece of wire. The company you work for is poorly equipped. You find a battery, a voltmeter, and an ammeter, but no meter for directly measuring resistance (an ohmmeter). You put the leads from the voltmeter across the terminals of the battery, and the meter reads 12.6 volts. You get a 100-meter spool of wire and connect it to the battery, with an ammeter in series with it to measure the current in the wire. The ammeter reads 5.00 amps. You then connect two spools (200 meters) of the same type wire and connect it to the battery, again with the ammeter in series to measure the current. The ammeter reads 2.87 amp. Even though the equipment you have available to you is limited, your boss assures you of its high quality: The ammeter has very small resistance, and the voltmeter has very large resistance. (a)What is the resistance of 1 meter of wire? Table   1 (b) You measure the thickness of the wire and it is 1.28 mm. What is the wire’s resistivity? (c) Given the resistivity in the Table   1, what is the material in the wire?   

Material Resistivities at 20o C (10-8 Ω-m) Silver 1.47 Copper 1.72 Gold 2.44 Steel 20 Aluminum 2.75 Tungsten 5.75

Answer 1