Question

You just landed a job as an assistant to an electrician who is working on a building site. He is making use of long single-conductor insulated wire for some of the connections in the complicated "smart building." A new shipment of spools of this wire has been delivered, and the electrician is not happy that it came from a manufacturer that he suspects is producing inferior wire. The electrician asks you to determine the resistance per unit length of the wire (in Ω/m) and provides you with a battery and a high-quality multimeter. Despite the quality of the meter, he suggests that you not use the ohmmeter to measure resistance, because the value of the resistance is so low that the meter is not likely to measure it accurately. You are puzzled as to how to go about this task. As the electrician runs off to attend to another task, he says, "Cut off a couple of different lengths of wire and use the battery and the multimeter." You put the multimeter in voltage mode across the terminals of the battery without a wire connected and measure 7.50 V. You then cut off two lengths of wire, one 5.00 m in length, and one 10.0 m in length. Connecting them one at a time to the battery through the multimeter in current mode, you find that there is a current of 5.07 A in the 5.00 m length of wire, and 3.15 A in the 10.0 m length of wire. Now you have enough information.

Answer 1