Your friend has an insulated copper wire and makes thefollowing two measurements

Question

Your friend has an insulated copper wire and makes thefollowing two measurements: 1. the wire's circular cross-sectionaldiamter is 1.675mm and 2. the wire is then wound on a spool,connected to a battery (4.750 V), and the wire's current is 350.0mA. Determine the length L of the wire. I understand part 1. but when it gets to part 2. is where Iget confused. Your friend has an insulated copper wire and makes thefollowing two measurements: 1. the wire's circular cross-sectionaldiamter is 1.675mm and 2. the wire is then wound on a spool,connected to a battery (4.750 V), and the wire's current is 350.0mA. Determine the length L of the wire. I understand part 1. but when it gets to part 2. is where Iget confused.

Explanation / Answer

Voltage V = 4.750 V Current i = 350 mA = 0.35 A Resistance R = V / i                      = 13.57 ohm Area of cross section A = 1.675 mm ^ 2 = 1.675 * 10 ^ -6m ^ 2 Ressitivity of copper = 1.72 * 10 ^ -8 ohm -m we know R = L / A from this length L = RA /                           = 1321.63m

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