Question

Wires aren't really ideal. The voltage drop across a current-carrying wire can be significant unless the resistance of the wire is quite low. Suppose a 100 ft extension cord is being used to provide power to an electric lawn mower. The cord carries a 10 Acurrent. The copper wire in a typical extension cord has a 1.3 mm diameter.

Part A

What is the voltage drop across a 100 ft length of wire at this current?

Express your answer using two significant figures.

?V =

Answer 1

First we need to find resistance R by using R = ?L/A
We know that L = 60 ft or 18.3 m, and ? of copper = 1.7 X 10-8 ? *m
Area can be found by ?r2.
D = 1.3mm or 0.0013 m, so r = 6.5 X 10-4 m
A = (6.5 X 10-4 m)2 ? = 1.33 X 10-6 m2

R = (resistivity of copper*length)/Area
R = (1.7 X 10-8 ? *m)(30.48 m)/ 1.33 X 10-6 m2 {1 ft = 0.3048}

R= 0..39 ?
Now we can use V= I x R to find the change in V.
V = 10 A x 0.39 ?
V = 3.9 V ~4 V........Answer

Hope it will help you. please rate the answer.