1) You have a summer job in the University ecology lab. Your supervisor asks you

Question

1) You have a summer job in the University ecology lab. Your supervisor asks you to duplicate an electromagnet that she has borrowed. She tells you that this electromagnet is made by wrapping a wire many times around a piece of iron and provides you with all the parts, the same type of wire of the same diameter and an identical iron core. What you need to know is how much wire to wrap around the iron. Unfortunately, you cannot simply unwrap the wire from the borrowed magnet because that will destroy it. On the side of the electromagnet, it tells you that when a potential difference of 12 V is put across the ends of its wire, there is a current of 0.06 A through the wire. With a brilliant flash of insight, you realize that the cross-sectional area and the conductivity is the same for both the magnet's wire and the wire you have, so you can find the length with a simple experiment. You cut off a 100-foot piece of identical wire from your supply, attach it to a 1.5-V flashlight battery and measure a current of 0.10 A through that wire. Eureka! you can now find the length of the magnet's wire.

Explanation / Answer

E = K P L I / A where K = specific resistivity (Ohm - circular mils/foot) P = phase constant = 2 (single phase) = 1.732 (three phase= L = wire length (ft) A = wire area E = K P L I / A

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