Question

The resistance of a wire varies directly with its length and inversely with the square of its diameter. If 100 feet of wire with diameter 0.01 inch has a resistance of 10 ohms, what is the resistance of 140 feet of the same type of wire if its diameter is 0.01 inch

Answer 1

14 ohms

Explanation:

The resistance varies directly with length, so increasing the length by a factor will increase the resistance by the same factor.

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The length of the wire increased by a factor of 1.4 from 100 ft to 140 ft. That means the resistance will increase by a factor of 1.4 from 10 ohms to 14 ohms. (The diameter did not change.)

The longer wire will have a resistance of 14 ohms.