A wire is stretched so that its radius of cross section becomes half, then resistance of wire will be:
Correct answer: D. 16R
- A. 4R
- B. R/4
- C. 8R
- D. 16R
Explanation
If you stretch the wire till its radius is halved the previous value, then its length will increase 4 times to keep the volume constant. Resistivity remains the same as it depends upon the material of the wire. So, the new resistance will be R = 16R.
This question appeared on the NUMS 2021 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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