Resistance of a wire is r ohms. The wire is streched to double its length, then its resistance is ohms is:
Correct answer: B. 4r
- A. r/2
- B. 4r
- C. 2r
- D. r/4
Explanation
When a wire is stretched to double its length, its resistance R changes according to the formula: [R' = 2R] So, the resistance of the wire after it's stretched to double its length is 2r. When the length of a wire is doubled, its resistance increases proportionally. This is because resistance is directly proportional to the length of the wire (assuming the material and cross-sectional area remain constant). Therefore, option c is correct.
This question appeared on the KMU Centralized Admission Test 2022 paper, which you can sit online with every answer explained.
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About Resistance and Resistivity
Resistance measures opposition to current in a conductor and follows R = V/I for an ohmic conductor, while resistivity is an intrinsic property of the material. Questions use R = ρL/A, examine effects of length, cross-sectional area and temperature, and distinguish resistance, resistivity, conductance and conductivity.
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