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NDA 2023 GAT · General Knowledge · Current Electricity · easy

A wire of resistance R is uniformly stretched to double its length. Its new resistance is

Single correct option

A wire of resistance R is uniformly stretched to double its length. Its new resistance is
  1. A. 2R
  2. B. 4R
  3. C. R/2
  4. D. R/4
Show answer and solution

Answer: (B) 4R

Stretching keeps the volume constant, so doubling the length halves the cross-sectional area. Resistance = ρL/A therefore becomes ρ(2L)/(A/2) = 4R. Answering 2R forgets the change in area.
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Original question written in the NDA 2023 GAT pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake