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Let x is the resistance per unit length. Find the equivalent resistance.

1. R1 = x l1
2. R2 = x l2
3. R = R1 + R2
4. R = x (l1 + l2)

Correct answer: R = x (l1 + l2)

Solution

The resistance of a wire is directly proportional to its length. If the resistance per unit length is x, the total resistance for lengths l1 and l2 combined is x(l1 + l2).

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