A wire is stretched so that its length doubles while its volume stays constant. Its resistance becomes
Correct answer: C. four times
- A. double
- B. half
- C. four times
- D. unchanged
Explanation
Constant volume means doubling the length halves the cross sectional area, and since resistance is proportional to length over area, the effect is two multiplied by two, giving four times the original. Answering double accounts for the length change only. This is a favourite examination trick precisely because the area change is easy to overlook.
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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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