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Next: Example 7.2: Equivalent resistance Up: Electric Current Previous: Worked Examples

Example 7.1: Ohm's law

Question: What is the resistance at $0^\circ $C of a $1.0$m long piece of no. 5 gauge copper wire (cross-sectional area $16.8\,{\rm mm}^2$)? What voltage must be applied across the two ends of the wire to produce a current of 10A through it?
Answer: Using the basic equation $R=\rho\,L/A$, and the value of $\rho$ for copper given in Tab. 2, we have

R = \frac{(1.7\times 10^{-8})\,(1.0)}{(16.8\times 10^{-6})} = 1.0\times 10^{-3}\,

Using Ohm's law $V=I\,R$, we obtain

V = (10)\, (1.0\times 10^{-3}) = 1.0\times 10^{-2} \,{\rm V}.

Richard Fitzpatrick 2007-07-14